Entire Report - Annual 2011

National Overview

NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

Issued January 19, 2012: The data presented in this report are final through August and preliminary from September-December. Ranks, anomalies, and percent areas may change as more complete data are received and processed.

National Temperature and Precipitation Analysis

In 2011, the contiguous United States (CONUS) average annual temperature of 53.8 degrees F (12.1 degrees C) was 1.0 degree F (0.6 degree C) above the 20th century average, and was the 23rd warmest year on record. Since 1895, the CONUS has observed a long-term temperature increase of about 0.12 degree F (0.07 degree C) per decade. Precipitation across the CONUS in 2011 was 0.36 inch below the long-term average (LTA). Over the long-term, precipitation averaged across the CONUS, is increasing at a rate of about 0.18 inch (4.6 mm) per decade.

On a statewide and seasonal level, 2011 was a year of temperature and precipitation extremes for the United States. Most states east of the Rockies had annual temperatures which were above average. Sixteen states had annual temperatures among their ten warmest. Delaware was record warm for the period, with an annual temperature of 58.2 degrees F (14.6 degrees C), or 3.5 degrees F (1.9 degrees C) above average. Texas had its second warmest year on record, with an annual temperature anomaly of 2.2 degrees F (1.2 degrees C), just shy of the annual record of 2.5 degrees F (1.4 degrees C) set in 1921. The western states had annual temperatures which were near average, with the exception of Oregon and Washington, which were the only two states with annual temperatures below average.

Although the CONUS as a whole was drier than average for the year, several states and cities were record wet during the year. Above-average precipitation was widespread across the northern CONUS during 2011, with the wettest part of the country being the Ohio Valley and Northeast. Seven states across the two regions — Connecticut, Indiana, Kentucky, New Jersey, New York, Ohio, and Pennsylvania — had their wettest year on record. Below-average precipitation was present across the West, and along the southern tier of the country. Georgia (5th driest) New Mexico (6th), Louisiana (7th), and South Carolina (8th) had annual precipitation totals among their ten driest. Texas was record dry for the year, with 14.89 inches (378 mm) of precipitation — 13.03 inches (338 mm) below the 20th century average. The year 2011 surpassed 1917 as the driest year on record for Texas, when 14.99 inches (381 mm) of precipitation was observed across the state. When the wetter-than-average conditions across the northern CONUS are averaged with the drier-than-average conditions across the southern CONUS, they nearly cancel each other out in the nationally averaged precipitation total. When the precipitation extremes are combined cumulatively, like in the U.S. Climate Extremes Index (CEI), they tell a different story. The combined percent area of the country experiencing either extremely-wet or extremely-dry conditions during 2011 was record high at 58 percent.

A list of select cities breaking annual temperature and precipitation records during 2011 can be found here.

Seasonal highlights in 2011 include a cooler-than-average winter (December-February) across much of the CONUS, with the coolest temperature anomalies (the temperature compared to the 20th century average) anchored across the Southeast. Spring (March-May) brought precipitation extremes to much of the CONUS, with ten states across the northern U.S. having a wettest spring on record, with flooding occurring across the Upper Midwest and the Ohio and Mississippi Valleys. The Southern Plains were extremely dry during spring, a precursor for the record drought which persisted into summer. Wildfires ravaged the Southern Plains and Southwest during spring, with record acreage burned during the 3 months. Numerous tornadoes impacted the Southeast in April, with 748 confirmed during the month — a new national record for any month. Summer (June-August) 2011 was the second warmest thee months on record for the CONUS, with much of the U.S. having much-above-average temperatures, with the exception of the Northwest. Oklahoma and Texas both exceeded the previous records for warmest summer on record for any state. Hurricane Irene, the first land-falling U.S. hurricane in three years, made three landfalls along the Atlantic coast in late August, causing damage from the Carolinas to Vermont.

This annual report places the temperature and precipitation averages into historical perspective, while summarizing the notable events that occurred in 2011. More detailed analysis on individual months can be found through the Climate Monitoring home page.

Top Ten U.S. Weather/Climate Events for 2011

The following is a list for the top ten U.S. weather/climate events which occurred during 2011. These events were selected by a panel of weather/climate experts from around the country.

Rank Event
1 April 25th–28th Tornado Super Outbreak
2 Southern U.S. Drought (spring–summer)
3 Joplin, Missouri EF-5 Tornado (May 22nd)
4 Mississippi River and Ohio River Flooding (spring)
5 Oklahoma and Texas — Hottest 3-month Statewide Temperatures on Record (summer)
6 Hurricane Irene (August)
7 Northern Plains and Upper Midwest Flooding (early summer)
8 U.S. Wildfire Season (spring-summer)
9-tie Tropical Storm Lee (September)
9-tie April 14th–16th Tornado Outbreak

Seasonal Analysis


The 2010/11 winter season was marked by anomalously cold temperatures across the eastern half of the country, with the coolest temperature anomalies across the Southeast. The CONUS had an average winter temperature of 32.2 degrees F (0.1 degrees C), which was 0.7 degrees F (0.4 degrees C) below average. Florida had its tenth coldest winter on record. A strong negative phase of the Arctic Oscillation (AO) was associated with much-cooler-than-average temperatures across the eastern U.S. during the first half of winter. Florida and Georgia both had their coolest December on record, with temperature anomalies of more than 9 degrees F (5 degrees C) and 8 degrees F (4 degrees C) below average, respectively. By mid-January, the negative phase of the AO had subsided, and more seasonal to above-average temperatures returned to the Southeast by February. A different scenario played out across the West, with the winter season beginning warmer than average but ending much cooler than average. On the regional scale, only the West climate region had winter temperatures that were above normal. The Southwest and Northwest were near-normal, while all climate regions east of the Rockies were cooler than normal.

The presence of La Niña during winter influenced precipitation patterns during the season. The 3-month average CONUS precipitation of 5.71 inches (145 mm) was 0.76 inch (19 mm) below average. Drier-than-average conditions were observed across much of the southern U.S., from New Mexico to Virginia. Louisiana, Arkansas, Alabama, Mississippi, and Virginia had winter precipitation totals ranking among their ten driest. A persistent storm track brought above-average precipitation to the Northern Plains and Upper Midwest, where Montana, North Dakota, South Dakota, and Minnesota had a winter season ranking among the ten wettest. The above-average precipitation across the Northern Plains contributed to a much-above-average snowpack across the region. A massive winter storm impacted the central U.S. during February, dropping 2 feet (61 cm) of snow in the Chicago area. The storm caused at least 1.8 billion U.S. dollars worth of damage, and killed at least 36 people. The storm track across the Northern U.S. and few storms making it into the South and Southeast are consistent with La Niña conditions. The wetness across the Northern Plains primed the region for spring and summer flooding, while the dryness in the South was a precursor to the spring and summer drought.


The spring (March-May) average CONUS temperature of 52.3 degrees F (11.3 degrees C) was 0.5 degree F (0.3 degree C) above average. Regional spring temperatures were consistent with an upper level trough across the West and an upper-level ridge across the South and East. Above-normal temperatures were present from New Mexico, across the South, and along the Eastern Seaboard. Texas had its second warmest spring on record. The West, Northwest, and Northern Plains were cooler than average during spring — Washington had its fifth coolest spring on record and Oregon its seventh coolest.

The precipitation (and lack of precipitation) was the big story during spring 2011. The nationally-averaged precipitation during the season was 1.41 inches (39 mm) above average. Consistent with a spring La Niña, a persistent pattern set up in which the Pacific Northwest and Northern Rockies saw frequent storm systems and invasions of cold air. In the South, storm systems repeatedly developed in the mid-Mississippi Valley, just a few hundred miles from the drought-stricken Southern Plains, then raced northeastward. In general, drought intensified in the South, while much of the Northeast, Ohio Valley and Northwest were subjected to historic or near-historic wetness. A total of 10 states were record wet during spring, and an additional 11 states had spring precipitation totals ranking among their ten wettest. The storms brought snow pack totals across much of the West to more than 180 percent of normal. The record precipitation and snow melt caused significant flooding in late spring and early summer along several rivers, including the Mississippi, Ohio, Missouri, Souris, and James. The runoff from the precipitation put significant stress on the levee systems along these rivers, and several levees were deliberately breached to flood farm lands and protect cities. In contrast to the wetness, Texas was record dry for the three-month period. Its statewide-averaged precipitation for spring was a paltry 2.56 inches (65 mm), more than 5 inches (127 mm) below normal. The dryness across the Southern Plains was associated with record wildfire activity during the spring period, when approximately 3.2 million acres (1.3 million hectares) burned — a new spring record. The active storm pattern brought a record-breaking severe weather season to the South and Southeast. As strong storms moved into the warm and moisture-rich atmosphere across the Southeast, 1,155 tornadoes were spawned, killing hundreds of people and causing over 20 billion U.S. dollars worth of damage.


The summer period (June-August) was warm for much of the CONUS, with only Oregon and Washington having summertime temperatures ranking among the bottom third of their historical distributions. The CONUS, as a whole, had its second warmest summer period on record with an average temperature of 74.5 degrees F (23.6 degrees C), 0.1 degree F (0.1 degree C) below the warmest summer on record in 1936. A persistent ridge across the eastern U.S. brought the epicenter of the hot temperatures to the Southern Plains, where New Mexico, Texas, Oklahoma, and Louisiana had their warmest summer on record. The statewide average summer temperature of 86.9 degrees F (30.5 degrees C) in Oklahoma marks the warmest three-month period for any state on record. During the summer of 2011, all states across the contiguous U.S., with the exception of Vermont, experienced at least one day with a location having a daily maximum temperature exceeding 100 degrees F (37.8 degrees C).

The drought across Texas was amplified during the summer of 2011, due to the very warm temperatures and the lack of precipitation. The state had its driest summer on record with a statewide average of 2.44 inches (62.0 mm) of rain accumulating. This is 5.29 inches (134.4 mm) below the long-term average, and 1.04 inches (26.4 mm) less than the previous driest summer in 1956. At the end of August, 81 percent of Texas was in the worst category of drought (D4, 'Exceptional' Drought), and analysis of tree-ring records dating back to 1550 indicated that the summer of 2011 drought is matched by only one summer (1789) in the 429-year tree-ring record. A persistent dome of high pressure was present for much of the summer across the Southern Plains, limiting storms from entering the region and causing temperature to soar. The Northeast was wetter than average during the summer period, partially because of Hurricane Irene bringing heavy rainfall to the region the last week of August. Connecticut and New Jersey were record wet for the summer. As a whole, the CONUS was drier-than-average with a nationally average precipitation total 0.9 inch (23 mm) below the LTA.


Although autumn (September-November) 2011 brought several extremes to the U.S., it was a significantly quieter season compared to the spring and summer. The average autumn temperature for the CONUS was 1.3 degrees above average. Most states had autumn temperatures near average, while Massachusetts, Rhode Island, and Vermont had their record warmest fall. Eight other states had an average temperature that was one of the ten warmest on record. Conversely, four states in the Southeast and along the Gulf Coast had below-average autumn temperatures.

Two significant storms impacted the CONUS during autumn. Tropical Storm Lee made landfall along the Louisiana coast on September 4th, and moved along a frontal boundary into the Ohio Valley and eventually into the Northeast. The storm brought much needed precipitation to the drought stricken Gulf Coast, but added to the annual precipitation totals of the Ohio Valley and Northeast. An early season storm brought heavy snow accumulations to the northeastern United States on October 29th-31st. The heavy, wet snow falling on the autumn foliage, combined with strong winds, caused havoc across the region. During autumn, the western half of the CONUS had precipitation which was near to slightly below the LTA. Beneficial precipitation fell across the core drought areas of Texas and Oklahoma. Minnesota had its third driest autumn on record. In contrast, many states across the Ohio Valley and Northeast had a very wet autumn. Pennsylvania and Ohio were both record wet for the period, and five other states had autumn precipitation ranking among their ten wettest.

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Alaska Annual Summary

Alaska temperatures in 2011 were above the 1971-2000 average, continuing the upward trend of the last 20 years. However, there was variation between the seasons. Winter temperatures in 2010-2011 were 0.4 degrees F (0.2 degrees C) below average. Spring temperatures were 0.9 degrees F (0.5 degrees C) below average, summer temperatures were 0.7 degrees F (0.4 degrees C) below average, and fall was 0.4 degrees F (0.2 degrees C) warmer than the average. For the annual period, Alaskan temperatures were 0.2 degrees C above average, driven almost entirely by very warm temperatures in December (third warmest December).

Precipitation in Alaska in 2011 was slightly above average. The winter season brought near-normal precipitation to Alaska, while the spring was much drier than average. Summer was wetter than average across Alaska and autumn precipitation was slightly below average.

In November, a large and powerful extratropical cyclone slammed into western Alaska, with extremely high tides, strong winds, heavy rain, and blizzard conditions. Winds gusted to over 80 mph (130 km/hr) and the storm surge topped 8 feet (2.4 m), marking the strongest storm to impact the region in decades.

Very Warm/Cold and Wet/Dry Percentages

One way to assess the magnitude of warm/cold and wet/dry episodes is to compute the percent area of the contiguous United States that was "very warm/very cold" and that which was "very wet/very dry". The figures above depicts these values for each month in the past 30 years. These percentages are computed based on the climate division data set. Those climate divisions having a monthly average temperature/precipitation in the top ten percent (> 90th percentile) of their historical distribution are considered "very warm/very wet" and those in the bottom ten percent (< 10th percentile) are "very cold/very dry".

During 2011, the U.S. experienced a cooler-than-average winter, which transitioned into a warm spring, summer, and autumn. In terms of the area of the contiguous U.S., 18 percent experienced temperatures that were in the bottom 10th percentile or categorized as "very cold" in December 2010. This definition correlates well with "much below normal" in terms of NCDC ranking methods. The extremely cool temperatures dissipated during January and February. The percent area of the country experiencing “very cold” conditions reached its highest value of 2011 during May, when it reached 22.7 percent. Most of those cool temperatures were present across the West, where Washington, Oregon, and Wyoming had a top ten cool month. Influenced by a strong Bermuda High and dome of high pressure, “very warm” conditions prevailed for April (22 percent of the country), June (29.7 percent), July (48.8 percent), August (43.5 percent), and September (25.44). The warm season, which as defined at April-September, was the seventh warmest for the CONUS, and Texas and Oklahoma were record warm.

Large areas of the CONUS experienced “very wet” and “very dry” conditions during 2011. The wetter-than-average conditions across the northern regions of the CONUS were counterbalanced by drier-than-average conditions across the southern regions. The percent area of the country experiencing very wet conditions peaked in April, when 24.3 percent of the CONUS was “very wet”. The smallest percent area of the country classified as “very wet” during 2011 was in June when the percent area dropped to 6.7 percent. The drought across the Southern Plains and Southeast contributed to large areas of the CONUS being “very dry” in 2011. The percent area of the U.S. as “very dry” peaked in August at 21.7 percent and again in December at 25.0 percent. A large area of the western U.S. was near-record dry during December 2011.

When the area of the country that experienced “very warm” conditions in the summer period (June, July and August) are averaged, the total area extent of 40.7 percent surpasses the previous record of 38.1 percent set in 1934, the fourth warmest summer on record. The effects of the record warmth in the Southern Plains during the summer period were compounded with the parched soils. More than 16 percent of the country was considered “very dry” most of it concentrated in the southern plains. The area of “very warm” conditions combined with “very dry” conditions was only second to 1936.

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Climate Extremes Index

The U.S. Climate Extremes Index (CEI) measures the occurrence of several types of climate extremes, such as record or near-record warmth, dry spells or rainy periods. In 2011, extremes in both temperature and precipitation were observed around the country and had a large impact on several regions. Persistent drought plagued much of the South and southeastern U.S., while parts of the Ohio Valley and the Northeast experienced record rainfall. In addition, much of the Mid-Atlantic, Northeast and South experienced much-above-average temperatures throughout the year, while the Pacific Northwest remained relatively cool. For the contiguous U.S., the spatial extent of extremes, as measured by the CEI, during the annual season was approximately 12 percent greater than the historical average. This above-average extent of extremes was primarily due to extensive extremes in warm maximum and minimum temperatures, extreme wetness and dryness, as denoted by the Palmer Drought Severity Index (PDSI), and an abundance of days in which precipitation fell. Regions which experienced some of the most wide-spread extremes during 2011 include the South, Southeast and Northeast. Nearly half of the South region was impacted by a blend of extremes in warm maximum and minimum temperatures as well as PDSI dryness. Over one third of the Southeast was impacted by a combination of warm maximum and minimum temperatures as well as PDSI dryness. Over 70 percent of the Northeast experienced extremes in warm maximum and minimum temperatures in addition to PDSI wetness, extremes in 1-day precipitation, and an abundance of days in which precipitation fell. During 2011, the most prominent and widespread extremes occurred during two seasons: spring and summer.

At the National level, the spring season was near normal for both temperature and precipitation, despite large regional differences. Warm extremes were confined to the Deep South and parts of the Mid-Atlantic states, while cool extremes occurred across the Northwest and northern-tier states. Record wet conditions persisted across much of the Ohio Valley and into the Northeast as well as across parts of the Northwest. Record dryness existed across Texas with much below average precipitation realized in other parts of the South.

For the contiguous U.S., the spatial extent of the CEI was nearly twice the historical average during spring. Factors contributing to the elevated 2011 spring value were large footprints of warm and cold maximum temperatures, areas of extreme PDSI wetness, and an abundance of days in which precipitation fell. Regions of the country which were most significantly impacted by extremes during the spring season were the Northwest, Northern Rockies and Plains, South and Northeast regions. In fact, the Northeast and the South regions had their 2nd highest extent of extremes on record with 57 percent and 43 percent of each region affected by extremes during this season, respectively.

The summer season was second warmest on record for the U.S. with much above average temperatures to record heat extending from the South though the Mid-Atlantic states. Precipitation received from Hurricane Irene impacted parts of the Northeast while drought conditions persisted across one third of the U.S. The CEI for the contiguous U.S. was approximately twice the historical average during summer. A record 63 percent of the South region was impacted by extremes during the summer months. Approximately 96 percent of the region succumbed to extremes in warm maximum temperature, 95 percent to extremes in warm minimum temperature and 78 percent to extremes in PDSI dryness. For the Southeast, extremes impacted a record 53 percent of the region with the largest contribution coming from extremes in warm maximum temperature, warm minimum temperature and PDSI dryness.

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NOAA's National Climatic Data Center is the world's largest active archive of weather data. The preliminary temperature and precipitation rankings are available from the center by calling: 828-271-4800.

NOAA works closely with the academic and science communities on climate-related research projects to increase the understanding of El Niño and improve forecasting techniques. NOAA's Climate Prediction Center monitors, analyzes and predicts climate events ranging from weeks to seasons for the nation. NOAA also operates the network of data buoys and satellites that provide vital information about the ocean waters, and initiates research projects to improve future climate forecasts.

Global Analysis

Contents of this Section:

2011 Global Significant Weather and Climate Events2011 Global Significant Weather and Climate Events

Global Highlights

  • This year tied 1997 as the 11th warmest year since records began in 1880. The annual global combined land and ocean surface temperature was 0.51°C (0.92°F) above the 20th century average of 13.9°C (57.0°F). This marks the 35th consecutive year, since 1976, that the yearly global temperature was above average. The warmest years on record were 2010 and 2005, which were 0.64°C (1.15°F) above average.

  • Separately, the 2011 global average land surface temperature was 0.8°C (1.49°F) above the 20th century average of 8.5°C (47.3°F) and ranked as the eighth warmest on record. The 2011 global average ocean temperature was 0.40°C (0.72°F) above the 20th century average of 16.1°C (60.9°F) and ranked as the 11th warmest on record.

  • La Niña, which is defined by cooler-than-normal waters in the eastern and central equatorial Pacific Ocean that affects weather patterns around the globe, was present during much of 2011. A relatively strong phase of La Niña opened the year, then dissipated in the spring before re-emerging in October and lasting through the end of the year. When compared to previous La Niña years, the 2011 global surface temperature was the warmest observed during such a year.

  • The 2011 globally-averaged precipitation over land was the second wettest year on record, behind 2010. Precipitation varied greatly across the globe. La Niña contributed to severe drought in the Horn of Africa and to Australia's third wettest year in its 112-year period of record

Global Temperatures

The year 2011 tied with 1997 as the 11th warmest year since records began in 1880. The annually-averaged temperature over global land and ocean surfaces was 0.51°C (0.92°F) above the 20th century average of 13.9°C (57.0°F). This marks the 35th consecutive year (since 1976) that the yearly global temperature was above the 20th century average. The warmest years on record were 2010 and 2005, which were 0.64°C (1.15°F) above average. Including 2011, all eleven years in the 21st century so far (2001–2011) rank among the 13 warmest in the 132-year period of record. Only one year during the 20th century, 1998, was warmer than 2011.

21st Century (2001–2011) Annual Temperature Ranks

The following table list the global combined land and ocean annually-averaged temperature rank and anomaly for each of the years to date in the 21st century.

21st Century
1 = Warmest
Period of Record: 1880–2011
Anomaly °C Anomaly °F
2011 11 0.51 0.92
2010 1 (tie) 0.64 1.15
2009 7 (tie) 0.58 1.04
2008 13 0.50 0.90
2007 7 (tie) 0.58 1.04
2006 6 0.59 1.06
2005 1 (tie) 0.64 1.15
2004 9 0.56 1.01
2003 4 0.61 1.10
2002 5 0.60 1.08
2001 10 0.54 0.97

Natural climate patterns that persist for days, months, or even years can affect weather patterns around the world and impact the average global temperature. One such well-known global-scale pattern—the El Niño-Southern Oscillation (ENSO)—is a natural episodic fluctuation in sea surface temperature (El Niño) and the air pressure of the overlying atmosphere (Southern Oscillation) across the equatorial Pacific Ocean. Over a period of months to a few years, ENSO fluctuates between warmer-than-average ocean surface waters (El Niño) and cooler-than-average ocean surface waters (La Niña) in that region.

Two separate cool-phase La Niña events took place in 2011, according to NOAA's Climate Prediction Center (CPC). These events affected weather patterns in many parts of the world during the year and dampened the global temperature compared with the record warmth of the previous year, 2010 (which is tied for warmest with 2005). The coolest monthly global anomalies occurred during the beginning of the year, where both January and February each ranked as 17th warmest for their respective months. Monthly temperature anomalies increased as the La Niña episode waned and ENSO-neutral conditions emerged during May. June and July ranked as the seventh warmest for their respective months while August and September each ranked eighth warmest. La Niña conditions returned in October and moderately strengthened during the remainder of the year. Global monthly temperature anomalies during this period cooled compared to those during the middle of the year.

With CPC ENSO records dating back to 1950, 2011 ranked as the warmest "La Niña year" in the 1950–2011 period of record. Two of the three warmest years on record (2010 and 1998) are "El Niño years". A La Niña (El Niño) year is defined here as occurring when the first three months of a calendar year meet the La Niña (El Niño) criteria as defined by the CPC.

Temperature anomalies color coded to show El Niño and La Niña years
Global Annual Temperature Anomalies

Separately, the average global land temperature was 0.83°C (1.49°F) above the 20th century average and ranked as the eighth warmest year on record. It was also the warmest annual global temperature over land during a La Niña year. The average monthly land temperature anomaly ranged from 0.45°C (0.81°F; January) to 1.12°C (2.02°F; April), a difference of 0.67°C (1.21°F).

Already well into the La Niña phase that began in mid-2010, the globally-averaged January ocean surface temperature was the 11th warmest January on record, but the warmest among all Januaries when La Niña was present. The ten warmest Januaries occurred during either El Niño or ENSO-neutral conditions. During the year, the global monthly ocean temperature anomaly ranged between 0.32°C (0.58°F; December) and 0.47°C (0.85°F; July), a difference of 0.15°C (0.27°F). For the period January–December, the ENSO-neutral conditions that were sandwiched by La Niña events at the beginning and end of 2011 contributed to a globally averaged ocean surface temperature anomaly of 0.40°C (0.72°F) above the 20th century average, the 11th warmest year on record. It was also the warmest global ocean temperature anomaly among all La Niña years. 2003 and 1998— both El Niño years—tie for the warmest years on record, at 0.51°C (0.92°F) above average.

January–December Anomaly Rank
(out of 132 years)
°C °F Year(s) °C °F
Land +0.83 ± 0.18 +1.49 ± 0.32 Warmest 8th 2007 +1.05 +1.89
Coolest 125th 1907 -0.56 -1.01
Ocean +0.40 ± 0.03 +0.72 ± 0.05 Warmest 11th 2003 +0.52 +0.94
Coolest 122nd 1909 -0.45 -0.81
Ties: 2007
Land and Ocean +0.51 ± 0.08 +0.92 ± 0.14 Warmest 11th 2005, 2010 +0.64 +1.15
Coolest 122nd 1908, 1909, 1911 -0.42 -0.76
Ties: 1997
Northern Hemisphere
Land +0.94 ± 0.24 +1.69 ± 0.43 Warmest 6th 2007 +1.19 +2.14
Coolest 127th 1884 -0.65 -1.17
Ocean +0.39 ± 0.04 +0.70 ± 0.07 Warmest 13th 2005 +0.54 +0.97
Coolest 120th 1910 -0.46 -0.83
Land and Ocean +0.60 ± 0.14 +1.08 ± 0.25 Warmest 10th 2010 +0.75 +1.35
Coolest 123rd 1912 -0.43 -0.77
Ties: 2001
Southern Hemisphere
Land +0.52 ± 0.11 +0.94 ± 0.20 Warmest 14th 2005 +0.87 +1.57
Coolest 119th 1917 -0.71 -1.28
Ties: 1991
Ocean +0.41 ± 0.03 +0.74 ± 0.05 Warmest 11th 1998 +0.54 +0.97
Coolest 122nd 1911 -0.46 -0.83
Land and Ocean +0.43 ± 0.06 +0.77 ± 0.11 Warmest 12th 1998 +0.58 +1.04
Coolest 121st 1911 -0.47 -0.85

The 1901-2000 average combined land and ocean annual temperature is 13.9°C (56.9°F), the annually averaged land temperature for the same period is 8.5°C (47.3°F), and the long-term annually averaged sea surface temperature is 16.1°C (60.9°F).

Top Ten Global Weather/Climate Events for 2011

The following table list the top ten global weather/climate events of 2011. These events are listed according to their overall rank, as voted on by a panel of weather/climate experts. For additional information on these and other significant 2011 climate events, please visit NCDC's Top Ten Global Events webpage.

Rank Event When Occurred
1 East Africa Drought Ongoing
2 Thailand Flooding July–October
3 Eastern Australia Flooding December 2010–February 2011
Austral Summer
4 Consecutive La Niña Events Throughout 2011
5 Brazil Flash Floods January 6th–12th
6 Tropical Storm Washi (Sendong) December 16th–17th
7 Arctic Sea Ice Extent Throughout 2011
8 Colombia Rainfall March–May
9 Mexico Drought Throughout 2011
10 European Drought September–November

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Regional Temperatures

Warmer-than-average temperatures occurred during 2011 for most of the world's surface. The greatest above-average annual temperature anomalies occurred across the Northern Hemisphere high latitude land areas, particularly central and northern Russia, Scandinavia, and Canada. Also noteworthy, it was warmer than average across the eastern half of the United States, Mexico, most of Europe and Africa, and the north central Pacific Ocean. Temperatures were below normal across the eastern and central Pacific Ocean, west central North America, and north and central Australia.

The map, above left, is created using data from the Global Historical Climatology Network (GHCN), a network of more than 7,000 land surface observing stations. Temperature anomalies are with respect to the 1961–1990 average. The map, above right, is a product of a merged land surface and sea surface temperature anomaly analysis developed by Smith et. al (2008). For the merged land surface and SST analysis, temperature anomalies with respect to the 1971–2000 average for land and ocean are analyzed separately and then merged to form the global analysis. For more information, please visit NCDC's Global Surface Temperature Anomalies page.

A natural hemispheric-scale climate pattern called the Arctic Oscillation (AO) can be a dominating driver of winter temperatures in the Northern Hemisphere. Its effects were particularly felt during January, when the AO was strongly negative. A negative AO is associated with cold polar air that spills southward into the mid-latitudes from the Arctic region and warm air that advects northward.

Due at least in part to this pattern, the contiguous United States reported its coolest January since 1994. December 2010 was also slightly below average, helping to bring the United States its second cooler-than-normal winter (December–February) in a row. In China, 2011 was also off to a cold start. It was the coolest January, behind 1977, since records began in 1961. In Europe, the UK reported its second coolest winter (behind 2009/10) since 1985/86.

Conversely, in the higher northern latitudes, Canada reported its sixth warmest winter since national records began in 1948. The warmest winter occurred the previous year (2009/10). Most of the above-normal temperatures occurred in the northern half of the country. Temperatures were more than 4°C (7°F) above normal for large areas of Nunavut, northern Quebec, and Labrador. The negative-phase AO contributed to these warm northern temperatures.

In the Southern Hemisphere, the summer (December 2010–February 2011) was Australia's coolest since 2001. These cooler temperatures can be attributed in part to the ongoing La Niña event. Cool conditions, in association with increased cloudiness and above-average rainfall, continued across Australia into March as nationally-averaged March daytime temperatures ranked as the coolest March on record. With cool conditions persisting into April and May, Australia had its coolest autumn (March–May) on record.

Parts of Western Europe reported record or near-record warmth during April. Germany experienced its second warmest April since national records began in 1881, behind April 2009, with the average nationwide temperature almost 4.4°C (7.9°F) above average. It was the warmest April on record across the United Kingdom, with temperatures 3°C to 5°C (5°F to 9°F) above normal in many areas, breaking the previous record set in 2007 by 0.5°C (0.9°F). This warmth also contributed to the UK's warmest spring on record (tied with 2007).

Spain experienced its third warmest May on record, behind 1964 and 2006. But in Australia, the effects of La Niña continued. Cool weather brought the country its seventh coolest May on record and it's coolest May since 2000, at 1.33°C (2.39°F) below averageIn contrast to Australia, New Zealand reported its warmest May since records began in 1909, with the temperature 2.2°C (4.0°F) above the monthly average. New Zealand also had its third warmest June on record, with the temperature 1.5°C (2.7°F) above the monthly average. .

Summer was warm across China. June 2011 was the second warmest June for the country since records began in 1951, July was the seventh warmest, and August was the fourth warmest on record.

In July, with ENSO-neutral conditions in place, maximum temperatures were above normal for all states and territories in Australia for the first month since April 2010. La Niña conditions during 2010/11 kept temperatures below normal across most of the country for more than a year.

The UK had its coolest average monthly July temperature since 2000. The average minimum temperature was the coolest since July 1980. Spain had its coolest July since 2002, although the temperature was only 0.1°C (0.2°F) below the 1971–2000 average. The cooler-than-average temperatures continued into August in some regions. Scotland and Northern Ireland had their coolest average monthly August temperatures since 1993.

In North America, a major heat wave contributed to the third warmest July on record for the United States. This warmth was followed by more heat, particularly in the South, giving the U.S. its second warmest August. The warmth in the United States during July and August contributed to the country's second warmest summer. Two states, Oklahoma and Texas, reported the highest U.S. summer temperatures for any state in any year since records began in 1895.

In Northern Europe, Finland had its fourth warmest summer since records began in the early 1900s. In Iberia, Spain rebounded from its cool July and reported its sixth warmest August on record since 1961. In the Southern Hemisphere, Australia had its fifth warmest August maximum temperature in the 62-year period of record.

As Northern Hemisphere fall (September–November) began, it was the warmest September in Spain since 1990 and fifth warmest in the past 50 years. The UK marked its warmest September since 2006 and sixth warmest in the last 100 years. It also reported its warmest October since 2006 and eighth warmest in the last 100 years. However, most of southern and western South America was cooler than average. According to the Argentina Meteorological Service (Servicio Meteorologico Nacional), several locations in Argentina experienced their coolest October in the past half century.

In Asia, China reported its sixth warmest October and third warmest November since national records began in 1951.

The November average monthly temperature in Norway was 4.6°C (8.3°F) above average, making this month the country's warmest November since records began in 1900. The average temperature for Northern Norway was 5.3°C (9.5°F) above normal, also a new November record. These warm temperatures helped give Norway its warmest autumn on record. It was also Finland's warmest autumn since 1938.

The average November temperature for Austria's high elevation stations was 2.6°C above average, giving this region the second warmest November in the country's 161-year period of record, behind 2006.

November 2011 was the second warmest November on record for the UK, behind 1994, at 2.9°C (5.2°F) above normal. It was also the second warmest autumn on record for the UK in more than a century, with temperatures 2.1°C (3.8°F) above average. November 2006 was the warmest at 2.3°C (4.1°F) above average. In Central England, autumn temperatures were the second warmest in at least 350 years.

In December, a strong positive Arctic Oscillation kept polar air contained to the very high northern latitudes and much warmer-than-normal temperatures were observed in lower, but still high, northern latitudes. Alaska reported its third warmest December on record and Northern Norway had its 10th warmest December in the 112-year period of record. In Europe, the UK had its sixth warmest December on record. This is more than 5°C (9°F) warmer than the record cold of the previous December (2010), when the Arctic Oscillation was strongly negative.

Australia temperatures were plagued by the La Niña that emerged in October. It was the country's coolest December since 2001.

For the year, in Northern Europe, the 2011 annually-averaged temperature for Norway was 1.8°C above average, tying with 1990 and 2006 as the country's warmest year on record. Finland tied with 1989 for its second warmest year on record, behind 1938, with March–December all warmer-than-average months. According to the Finnish Meteorological Institute, the average temperature for 2011 was 1.9°C (3.4°F) above the long-term average.

In Southern Europe, it was the warmest year on record for Spain, at 1.49°C above the 1971–2000 average.

In Western Europe, the UK reported its second warmest year on record, behind 2006. The UK Met Office also reported that the UK's seven warmest years have all occurred within the past decade.

Germany reported its fifth warmest year on record, with all months except July warmer than average. The annually-averaged temperature was 0.7°C above the 1981–2010 average.

For Austria's high elevation alpine stations, the average temperature was the warmest since records began in 1851, at 1.6°C above the 1971–2000 average, according to ZAMG. This surpassed the previous record set in 1994 by 0.3°C. The average temperature for the country's low elevation stations ranked as sixth warmest on record, at 1.2°C above average.

In the Southern Hemisphere, Australia experienced its first cooler-than-average year since 2001, due in part to the impacts of La Niña during most of 2011.

New Zealand, which experienced a year of extreme weather, both hot and cold, observed an annually-averaged temperature that was 17th warmest since records began in 1919, or warmer than about 80 percent of all years, according to NIWA.

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Global Precipitation

Global precipitation over land in 2011 was well above the 1961–1990 average for the second year in a row, ranking as the second wettest year on record, behind 2010. Precipitation anomalies were variable across the globe. It was wetter than normal across much of the northeastern United States, Central America, much of coastal South America, Australia, and northwestern China. It was particularly drier than normal in far southwestern Canada, the south central United States, northern Mexico, southern and northeastern China, Mongolia, Hawaii, and French Polynesia and Kiribati in the South Pacific Ocean.

La Niña conditions during much of 2011 brought plenty of precipitation to Australia, making 2011 the country's third wettest year since records began in 1900. The Australian Bureau of Meteorology also attributed a record warm eastern Indian Ocean to the extreme wetness. It was particularly wet at the beginning of 2011, as the country reported its second wettest summer (December 2010–February 2011) and wettest March on record. On a longer time scale, the two-year period 2010–2011 ranked as the second wettest such period on record.

However, in East Africa, two consecutive seasons of poor rainfall—the short Deyr rains from October to December and the long Gu rains that typically begin in early April but were late and scattered—resulted in one of the driest years since 1950/51, according to the UN's Office for the Coordination of Humanitarian Affairs (OCHA). Somalia, Ethiopia, Eritrea, Kenya, and Djibouti were majorly impacted. The lack of Deyr rains in October–December 2010 was attributed to the ongoing La Niña. On July 19th, the United Nations offically declared a famine in the southern Bakool and Lower Shabelle regions of Somalia, the first time famine has been declared in this country since 1992. Please see the July 2011 Global Hazards report for detailed information.

La Niña also played a role in the intense drought observed in northern Mexico and the south central United States. As of the end of November, Mexico was suffering from its worst drought since national records began in 1941. Five states in northern Mexico—Durango, Zacatecas, Chihuahua, Coahuila and San Luis Potosi—were the hardest hit. On average those states had received less than 60 percent of average rainfall for that time period. Devastating drought conditions were seen across much of the southern tier of the United States. Texas, Oklahoma, Louisiana, and New Mexico were particularly hard hit and billions of dollars in economic losses were incurred. Please see the annual U.S. and Drought reports for details.

While some parts the U.S. were extremely dry, other parts were record or near-record wet. Two major tropical storm systems, Hurricane Irene and Tropical Storm Lee, each brought heavy rainfall to much of the northeastern U.S. within about a one-week period during late August and early September, respectively. These systems contributed to several states, including heavily populated New York, reporting their wettest years on record. Please see the U.S. annual report for detailed precipitation information.

In October, two separate storm systems—a tropical depression from the Pacific and another system from the Caribbean—dumped nearly five feet (1520 mm) of rain in some areas across Central America from the 10th to the 20th. Honduras, Costa Rica, Guatemala, El Salvador, and Nicaragua were majorly impacted. Please see the October Global Hazards report for detailed precipitation information.

In India, rainfall during the Southwest Monsoon season (June–September) was near normal, at one percent above the long-term average for the country as a whole. According to the India Meteorological Department, precipitation ranged from 14 percent below normal in the northeast of the country to 10 percent above normal in Central India.

Conversely, Sindh Province in southern Pakistan had its wettest monsoon season on record, with three and a half times its average rainfall. Most of the rain fell in a four-week period from mid-August to early-September.

The East Asian Monsoon brought heavy precipitation to South Korea in 2011. The country had its wettest summer on record, according to the World Meteorological Agency (WMO). On July 27th, the capital city of Seoul, South Korea experienced its heaviest single-day rainfall (11.8 inches; 300 mm) since 1907.

Storms and heavy monsoon rains from late July to November contributed to the worst flooding in Thailand since 1942. Some areas were under six feet (two meters) of water. Other countries in Southeast Asia were affected by the heavy rainfall, including Cambodia, Myanmar, and Vietnam. Please see the November Global Hazards report for detailed precipitation information.

The WMO reported that, in Europe, both France and the Netherlands each had their driest spring on record. The Netherlands followed with its wettest summer on record.

Austria's precipitation was 15 percent below the 1971–2000 average, making this the driest year since 2003. Contributing to this dryness was November, which was Austria's all-time driest month on record.

In contrast, Norway reported its wettest year, with records dating back to 1900. According to Meteorologisk Institutt, on average, the country received 130 percent of average rainfall, breaking the previous record of 125 percent set in 1983.

Annual precipitation varied greatly across the UK. The UK Met Office reported that Scotland had its wettest year on record, at 122.2 percent of average, while it was the second and third driest years on record for East Anglia and the Midlands, respectively.

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Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global Historical Climatology Network Database. Bull. Amer. Meteorol. Soc., 78, 2837-2849.

Quayle, R.G., T.C. Peterson, A.N. Basist, and C. S. Godfrey, 1999: An operational near-real-time global temperature index. Geophys. Res. Lett., 26, 333-335.

Smith, T.M., and R.W. Reynolds (2005), A global merged land air and sea surface temperature reconstruction based on historical observations (1880-1997), J. Clim., 18, 2021-2036.

Smith, et al (2008), Improvements to NOAA's Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006), J. Climate., 21, 2283-2293.

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National Snow & Ice

NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

The 2010-2011 winter began with a bang for much of the Eastern U.S. with several snowstorms and cold temperatures impacting the Eastern Seaboard during December and January. However, the end of the winter season was much quitter when above normal temperatures returned to the region in February. The change in the weather regime coincided with the transition of the Arctic Oscillation (AO) from a near-record negative phase to a positive phase. Significant snowfalls occurred throughout the winter season across the Intermountain West, across the Northern Plains and into the Ohio Valley. The active pattern across these regions is consistent with the La Niña conditions which were present for the entire season across the equatorial Pacific. The heavy snowpack, combined with above-normal spring precipitation caused significant flooding across the Northern Plains and the Mississippi and Ohio Valleys when warm temperatures returned in late spring.

US Winter snow extent anomalies
U.S. Winter Snow Cover Extent Anomalies
Data Source: Rutgers Global Snow Lab

When conditions are averaged for the three-month winter period (December 2010 - February 2011), below-normal temperatures were anchored across the eastern half of the country, with above-normal temperatures for the Southwest. Drier-than-normal conditions were widespread across the South, Southeast, and into the Mid-Atlantic. Wet conditions were present for the Northern Plains, stretching into the Northeast. Snow cover extent, which is measured from NOAA satellites and provided by Rutgers Global Snow Lab, was above average for each winter month, stretching into the spring. Across the U.S., each month from December through April had snow cover extents were among the ten largest on record. The winter (December-February) average snow cover extent for the contiguous U.S. was 305,000 square miles (790,000 square km) above the 1981-2010 average and ranked as the fifth largest winter snow cover extent in the 1966-present period of record.

Western US Snowpack 1 May 2011
Western U.S. Snowpack
May 1, 2011
Source: USDA

Winter and spring mountain snowpack provide a crucial water source across much of the western United States. The total annual water budget for agriculture and human use in the mountainous West is based upon the amount of snow melt that will occur in spring and is proportional to the amount of snow on the ground. The annual snowpack typically reaches its maximum value at the end of March. This year, late season snowfall across the Central and Northern Rockies contributed to a much above average snow cover extent well into April. According to data from the USDA, as of May 1st, 2011, much above normal snowpack was observed from the Cascade Mountains, southward into the Sierra Nevadas, and across the Central and Northern Rockies. Snowpack values more than 180 percent of normal were widespread. Below-normal snowpack was observed across much of the Southern Rockies of Arizona, New Mexico, and southern Colorado. Some areas of New Mexico had snowpack totals below their 25th percentile. Alaska generally had near-normal snowpack at the end of the snow season. Slightly below-normal snowpack was present across the southern coasts of Alaska while above-normal snowpack was observed across the western regions of the state.

Select Significant Events

A strong blizzard hit Minnesota, Iowa, and Wisconsin on December 10th-12th 2010, bringing over a foot of snow to the region and sustained winds of 35 mph (56 km/hr). The 17 inches (43 cm) of snow that fell in Minneapolis was the 5th largest snowstorm accumulation ever for the city and the largest December snowfall on record. Minneapolis set a new December snowfall record with a monthly total of 33.6 inches (86 cm), the previous December record was set in 1969 when 33.2 inches (85 cm) of snow was reported. Data for the city goes back to 1884. The 22 inches (56 cm) which fell in Eau Claire, Wisconsin on the 11th is the highest single calendar day snowfall total in history for the city. An unusual aspect of the storm was the high snow-to-water equivalent, which represents how heavy the snow was. The heavy nature of the snow, as well as the amount and strong winds, contributed to the collapse of the Metrodome roof, home to several professional sports teams. Fortunately the building was empty at the time of the collapse, and no one was injured.

A low pressure system moved across the southern U.S. and interacted with another system moving from the Northern Plains the last week of December 2010. The two systems brought widespread snowfall from Minnesota, southward to Alabama and Georgia and along the Eastern Seaboard to Maine on December 24th-28th. Many locations in the Southeast experienced their first white Christmas on record, and many cities broke daily snowfall records because of the storm. As the system moved up the Atlantic Coast, it strengthened, bringing heavy snowfall to the major cities in the Northeast. Central Park in New York City received 20 inches (51 cm) of snow, marking the sixth largest snowfall there, while Boston received 18.2 inches (46 cm), the city’s eighth biggest snow storm on record. The 20.1 inches (52 cm) which fell at the Atlantic City International Airport was a single snowstorm record. The Northeast Snowfall Impact Scale (NESIS) score, which measures the areal extent of snow and impact of snow extent/depth on popuated areas, was a Category 3 (major).

The first major winter storm complex during 2011 impacted the eastern half of the United States between January 9th-13th, dropping over a foot (30.5 cm) of snow for many locations across the Central Plains, Midwest, Southeast, Mid-Atlantic, and Northeast. A significant freezing rain and icing event occurred across many portions of the South and Southeast. The event began across northeast Texas on the 9th where over 6 inches (15.2 cm) of snow accumulated. The upper level low pressure system progressed along the Gulf Coast, drawing moisture from the Gulf of Mexico, causing a large precipitation shield over the Southeast. Parts of Mississippi, Arkansas, Tennessee, Alabama, and Georgia received over 10 inches (25.4 cm) of snow by the 10th. Huntsville, Alabama received 8.9 inches (22.6 cm) of snow, marking the third largest snow storm on record for the city. Parts of the Atlanta metropolitan area received eight inches (20 cm) of snow, shutting down the city for days. In the North Carolina mountains, up to 20 inches (51 cm) of snow were reported. The storm system then moved northward along the Atlantic Coast, bringing heavy snow to the population centers of the Northeast. Blizzard conditions were reported in Boston for several hours on the 12th. The 24 inches (61 cm) which fell at Bradley International Airport in Windsor Locks, Connecticut broke the previous all-time greatest storm record of 21.9 inches (56 cm), set on February 12th, 2006. Six states declared states of emergency. After the event, 49 of 50 U.S. states (all except Florida) had snow on the ground. The preliminary NESIS score, was a Category 3 (major).

Water Vapor Imagery of 1 February Storm
Water Vapor Imagery of 1 February Storm
Source: NWS

On February 1st-3rd a large and powerful winter storm, dubbed the ‘Groundhog Day Blizzard’, hit the central and northern regions of the United States from New Mexico northward to Wisconsin, and eastward to New England. The storm stretched for thousands of miles, leaving behind at least five inches (12.7 cm) of snow in 22 states. The multi-faceted storm also brought an inch of ice to portions of the Ohio River Valley. Winds gusting upwards of 70 mph (113 km/hr) created widespread blizzard conditions, and snow drifts were reported as high as 10 feet (3 meters). Numerous highways were forced to close and thousands of flights were cancelled nationwide. The storm began across the Southern Plains on the 1st, where it dropped 1 to 2 feet (30.5 cm 61 cm) of snow across Texas, Oklahoma, and Missouri. The largest snow amounts occurred across northern Illinois and southern Wisconsin on the 2nd. At Chicago's O’Hare Airport, the 20.2 inches (51.3 cm) of snow was the third largest storm accumulation ever recorded for the city. Racine, Wisconsin observed 26 inches (66.0 cm) of snow during the event, breaking the city’s 48-hour and 72-hour snowfall records. Snowfall records date back to 1886 for Chicago and to 1896 for Racine. The storm then moved off into the Northeast on the 3rd, where it left behind a foot of snow. Damages from the storm exceeded one billion U.S. dollars.

Satellite Image of landfalling storms along U.S. West Coast 20 March
Satellite Image of landfalling storms
along U.S. West Coast 20 March 2011
Source: NASA

A series of large Pacific storms made landfall along the U.S. West Coast between March 18th-26th. The storms brought incredible amounts of rain and snow from Washington State to Southern California. These storms contributed to many high-elevation observation stations having impressive snowfall totals for the month and the winter season. Squaw Valley at Lake Tahoe, California reported 241 inches (612 cm) of snowfall during March 2011. Alpine Meadows, California reported 315 inches (800 cm) of snow on the ground after these storms moved through, and several snow observation stations in the Sierra Nevadas received as much as 145 inches (368 cm) during the 9-day period. The snow added to the amount of water contained in the snow pack measured by snow water equivalent (SWE). At the end of March, some high elevation stations in California had SWE values approaching 80 inches (203 cm). For California as a whole, the average snowpack was 48 inches (122 cm) on April 1st, 168 percent of average. At some locations in the Sierra Nevadas, the snow depth exceeded the height of the automated weather stations in the SNOTEL network, causing underestimates in the measurement of snow on the ground.


NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

Issued: 19 January 2012

The U.S. spring and summer of 2011 will likely be remembered as one of the most destructive and deadly tornado seasons to ever impact the nation. During the time period, there were seven individual tornado and severe weather outbreaks with damages exceeding one billion U.S. dollars, and total damage from the outbreaks exceeding 28 billion U.S. dollars. This represents the most property damage from severe weather in a single year since record keeping began in 1980. As of mid-January 2012, the 2011 confirmed tornado count stood at 1,625, with 93 tornado reports still pending for November and December. This places 2011 as the second or third most active year on record for number of tornadoes since the modern record began in 1950, depending on the confirmation rate of the end-of-year tornado reports. There were six EF-5 tornadoes confirmed during 2011, the strongest category on the Enhanced Fujita scale. This ties with 1974 as the most (E)F-5 tornadoes during a single year (Please note that NOAA switched form using the Fujita (F) scale to the Enhanced-Fujita (EF) scale in 2007). The annual total number of fatalities from tornadoes was 551, the most in the 62-year period of record.

Looking beyond the modern tornado record (1950-present), 2011 ties with 1936 as the second deadliest year for tornadoes in U.S. history. In 1925, 794 tornado-related fatalities were reported, the deadliest tornado year on record. The extensive damage and loss of life due to tornadoes during 2011 was a product of an above-average tornado year and strong tornadoes hitting densely-populated areas. During the year, the two largest tornado outbreaks on record for the nation impacted the southern U.S., and the single deadliest tornado since the modern record began in 1950 hit Joplin, Missouri.

The most active tornado period of the year was the spring season (March-May). During the three month period, there 1,150 confirmed tornadoes across the country, the most on record for any three month period. The most active month of the year was April, when 748 tornadoes were confirmed. This is the most on record for any month, surpassing May 2003 when there were 550 tornadoes. The extremely high tornado count during April was driven by two very large tornado outbreaks — the two largest tornado outbreaks on record. The tornado counts for the April 14th–16th and April 25th–28th outbreaks both surpassed the April 1974 Super Outbreak for number of tornadoes during a single outbreak. The 199 tornadoes on April 27th, was the most for any single day on record and the 316 fatalities on the same day was the most in the modern record for a 24-hour period. The May 22nd Joplin, Missouri tornado caused 3 billion dollars worth of damage and 158 fatalities, surpassing the previous records for damages and fatalities from a single tornado in the modern tornado record.

Significant Events

The April 14th–16th tornado outbreak was spawned from a strong upper-level low pressure system moving through the Central Plains. Very warm, moist air was advected northward ahead of the associated cold front. Behind the cold front, very cool Canadian air filtered into the central parts of the U.S., and the boundary between these two air masses was the trigger for the unprecedented tornado outbreak. Over the three days, 177 tornadoes occurred across 16 states (Oklahoma to North Carolina), surpassing the April 1974 outbreak as the most active tornado outbreak on record. The 30 tornadoes which were confirmed in North Carolina, where 22 of the fatalities were reported, was a state record. The damages from the outbreak will exceed 2.1 billion U.S. dollars, and there were 38 reported fatalities in all. The outbreak was the deadliest in the U.S. since 2008.

The April 25th–28th tornado outbreak occurred under similar circumstances as the April 14th–16th event, with a strong low pressure system moving through the center of the country. This was one of the largest, deadliest, and most destructive tornado outbreaks in the history of the United States. During the four days, there were 343 confirmed tornadoes which killed 321 people — both are records for a single outbreak. Alabama bore the brunt of the damage, where 240 people were killed, including 78 people from a single EF-5 in the northern portion of the state. Several metropolitan areas were directly impacted including Tuscaloosa, Birmingham, and Huntsville in Alabama and Chattanooga, Tennessee, causing the estimated damage costs to soar. Damages from the outbreak are expected to exceed 10.2 billion U.S. dollars.

The May 22nd Joplin, Missouri tornado was spawned from a severe thunderstorm moving from Kansas into Missouri during the late afternoon hours. The tornado was rated an EF-5 with winds in excess of 200 mph. The tornado was on the ground for 6 miles and had a maximum width of three-quarter miles as it moved through the densely populated southern portion of the town. The tornado killed 158 people and injured thousands more, making it the deadliest tornado in the 1950-present modern tornado record. Damages from this single tornado are expected to exceed 3 billion U.S. dollars, the most on record for a single tornado in U.S. history.

Additional information is available in the Spring 2011 Climate Extremes Special Report and the monthly tornado summaries.

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Hurricanes & Tropical Storms

NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

Atlantic Basin

2011 Season Summary:

The 2011 North Atlantic hurricane season had 19 named storms, seven hurricanes, and three major hurricanes. The 19 named storms tied with 2010, 1995, and 1887 as the third busiest year for tropical cyclones in the basin. The second most active tropical cyclone year for the Atlantic basin was 1933. An average season has 11 named storms, six hurricanes, and two major hurricanes. The seven storms which reached hurricane strength and the three that reached Category 3 status (major hurricane) are both near the average, despite the high number of tropical storms. One hurricane (Irene) and one tropical storm (Lee) made landfall in the U.S. during the 2011 season. Hurricane Irene was the first Hurricane since Ike in 2008 that made landfall in the nation.

The Accumulated Cyclone Energy (ACE) index of tropical cyclone activity also indicated an above-average season. The ACE index is used to calculate the intensity of the hurricane season and is a function of the wind speed of each tropical cyclone. The 2011 Atlantic hurricane season had an approximate ACE value of 125 (x104knots2), which is 20 percent above the 1981-2010 average ACE value of 104 (x104knots2). The highest ACE value on record of 250 (x104knots2) occurred in 2005. Although there were an extremely high number of tropical storms during the year, the near average number of hurricanes and major hurricanes kept the seasonal ACE value relatively low compared to more active years. The first eight storms of the season failed to reach hurricane strength, marking the first time in the Atlantic that this many consecutive storms in a single season failed to reach hurricane strength.

The above-average season was partially attributable to lower-than-average wind shear across the basin and warmer than average sea surface temperatures. The lower than average wind shear is consistent with the presence of La Niña conditions across the equatorial Pacific during most of the hurricane season. Drier-than-average conditions persisted as air from the African Sahara made its way into the middle layer of the atmosphere above the tropical Atlantic for most of the season. This likely inhibited many of the named storms from developing into stronger hurricanes.

Only two of 19 named storms, 11 percent of the storms, made landfall in the contiguous U.S. during the 2011 season, which is below average. Steering currents caused most of the storms that formed over the open waters of the Atlantic to curve out to sea, missing the U.S. as they moved northward and eventually northeastward. The storms that formed across the Caribbean were steered into Mexico and Central America. It should be noted that although only two named storms made landfall in the U.S., four storms — Arlene, Harvey, Nate, and Rina — made landfall across Central America and Mexico causing significant flooding, damage, and loss of life across those regions.

Hurricane Irene was the first hurricane to make landfall in the U.S. since Hurricane Ike hit the Gulf Coast in 2008. Irene formed from a tropical wave moving off the Cape Verde Islands on August 21st, and moved westward across the central North Atlantic. Irene made landfall on the 22nd over Puerto Rico as the storm strengthened into a hurricane. The storm then moved through the Bahamas as it strengthened to Category 3 strength and it curved more northerly in its track. Irene made landfall on the 27th near Cape Lookout, North Carolina as a Category 1 hurricane. The storm then moved back over the coastal Atlantic waters and made a second landfall near Little Egg Inlet, New Jersey, as a strong tropical storm. Irene moved over open water again, and made landfall as a tropical storm near Coney Island, New York on the 28th. Irene was a massive storm, with tropical storm force winds extending outward 300 miles (485 km). The storm was also slow moving as it traversed the Mid-Atlantic. Irene claimed at least 48 lives and caused over 7 billion U.S. dollars in damages in the U.S. and 3.1 billion U.S. dollars of damage in the Caribbean.

East Pacific Basin

2011 Season Summary:

The Eastern Pacific Basin experienced near average tropical cyclone activity during 2011. The basin had 15 names storms, 10 hurricanes, and six major hurricanes. On average the basin experiences 15 named storms, nine hurricanes and four major hurricanes. The ACE value of 121 (x104knots2) was slightly below the 1981-2010 average of 131 (x104knots2). The season got off to a strong start, with several storms developing early in June and July, when ENSO neutral conditions were observed across the equatorial Pacific. La Niña conditions re-developed in August, which is associated with increased wind shear across the eastern North Pacific, limiting tropical cyclone development.

The 2011 Hurricane season got off to an early start with Hurricane Adrian reaching Category 4 status in early June, with winds reaching 140 mph and a minimum central pressure 944 mb. The strongest storm of the season was Hurricane Dora, which reached Category 4 status with winds of 155 mph (just shy of Category 5 status) and a central minimum pressure of 929 mb during mid-July. Hurricanes Eugene, Hillary, and Kenneth all reached Category 4 strength during 2011, none of which made landfall.

The deadliest tropical cyclone of the 2011 East Pacific Hurricane season was Tropical Depression 12-E. The storm formed in mid-October and had tropical characteristics for only two days before making landfall and dropping copious amounts of rain over southwestern Mexico, Guatemala, Nicaragua, El Salvador, Honduras, and Costa Rica. Over a foot of rain was reported across the mountainous regions, causing extensive flooding and landslides. Nearly 40,000 people were directly impacted, and there were 80 confirmed fatalities.

Hurricane Kenneth, which formed in mid-November, was a unique storm, although it never directly impacted land. The hurricane reached Category 4 strength, with winds of 145 mph and a central minimum pressure of 943 mb. Kenneth was the latest-forming storm in the eastern North Pacific east of 140 degrees West since 1987 and the latest-forming storm since 1983. Kenneth was also the strongest storm to ever be observed this late in the season for the basin.

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NCDC added Alaska climate divisions to its nClimDiv dataset on Friday, March 6, 2015, coincident with the release of the February 2015 monthly monitoring report. For more information on this data, please visit the Alaska Climate Divisions FAQ.

Issued 19 January 2012
The data presented in this drought report are preliminary. Ranks, anomalies, and percent areas may change as more complete data are received and processed.
Contents Of This Report:
Graph showing National Palmer Z Index

National Drought Overview

graph showing percent area of the contiguous U.S. very wet and very dry for January-December 2011

On a month-by-month basis, 2011 was characterized by large areas of dry and large areas of wet weather. Nine months (all except February, October, and November) had ten percent or more of the country experiencing very dry (at the tenth percentile of the historical record or drier) precipitation anomalies, with two months (August and December) having more than a fifth (20 percent) of the country very dry. This was counterbalanced by large areas (ten percent or more of the country) experiencing very wet (monthly precipitation totals at the 90th percentile of the historical record or wetter) precipitation anomalies in February through May, September, and December. The spring months were especially wet with April and May having more than a fifth of the country very wet. When averaged together, the wet and dry anomalies resulted in the 14th driest January, 24th driest June, 19th driest July, and 29th driest August, nationally, in the 1895-2011 record. Large areas of the country also experienced unusually warm conditions. Ten percent or more of the contiguous U.S. was very warm (monthly temperatures at the 90th percentile of the historical record or warmer) during eight months (all except January, February, May, and October). Conditions were especially warm during the summer, with nearly half (49 percent) of the country very warm in July and over 40 percent very warm in August. The unusual and persistent warmth, especially during the growing season, increased evaporation and intensified local drought conditions. The monthly values for June, July, and August, when averaged together, resulted in 16 percent of the country very dry and 41 percent very warm, or a total of 57 percent very warm and/or dry. This is the second highest such summer total in the 1895-2011 record.

An important feature of the weather conditions in 2011 was the persistence of the wet and dry areas. Dry weather dominated the year in the Southwest to Southern Plains, especially during March-September, with dry weather prevalent across much of the Gulf Coast to Southeast from April to August, the western Great Lakes to Upper Mississippi Valley and parts of the Northern Plains from August to December, and Far West from August-September and November-December. Wet conditions were the rule across much of the West (except the Southwest) from March to July, the Northern Plains from January-August, the Midwest from February-May and September-December, and the Northeast from February-May and August-October, with widespread flooding frequently the result. The persistence of these dry and wet anomalies shows up clearly in the 2011 annual precipitation state and climate division rank maps.

Index maps:
Palmer Z

The year started out with areas of drought stretching from the Southwest and Central Plains to the Southeast, with moderate to extreme drought covering about 18 percent of the country (based on the U.S. Drought Monitor [USDM]). By the end of spring, drought had expanded and intensified, especially in the South, with 21 percent of the country in moderate to exceptional drought. The heat and dryness of summer further expanded and intensified drought, with expansion occurring in the Ohio to Mid-Mississippi valleys and about 28 percent of the U.S. classified in the moderate to exceptional drought categories. Some contraction occurred in the drought area during the autumn and early winter months, especially in the Midwest to Central Gulf Coast, but drought developed in the Upper Mississippi Valley, Northern Plains, and Far West, with about 27 percent of the country in moderate to exceptional drought by year's end. The percent area of the U.S. experiencing the worst USDM category (D4, exceptional drought) reached a peak of about 10 percent during the summer and early fall, which is a record in the 12-year history of the USDM. Drought continued during 2011 in Hawaii, but not as severe as it was in 2010.

Percent of US Area in Moderate to Exceptional Drought since 2000 (based on USDM)

The percent area* of the contiguous U.S. experiencing moderate to extreme drought (based on the Palmer Drought Index) started the year at about 18 percent, grew steadily to a peak of about 29 percent during the summer, then contracted slightly during the last two months, ending the year at about 25 percent. The Palmer Drought Index data go back 117 years.

Percent of US Area in Moderate to Extreme Drought since 1900 Percent of US Area in Moderate to Extreme Drought since 1996

*This drought statistic is based on the Palmer Drought Index, a widely used measure of drought. The Palmer Drought Index uses numerical values derived from weather and climate data to classify moisture conditions throughout the contiguous United States and includes drought categories on a scale from mild to moderate, severe and extreme.


Regional Drought Overview

map showing VegDRI (Vegetation Drought Response Index) for October 2, 2011

The drought epicenters during 2011 were the Southwest to Southern Plains, the Central Gulf Coast to Southeast, and Hawaii. Secondary drought areas developed in the Midwest, Upper Mississippi Valley to Northern Plains, and Far West. Low stream, reservoir and stock pond levels, and depleted soil moisture combined with high temperatures and evaporation to ravage agricultural (pasture, range and crop) lands as the growing season progressed.

Southwest and Southern Plains:

Percent area of Southwest (AZ-NM-CO) in drought, March-December 2011
The Southwest (Arizona-New Mexico-Colorado) drought peaked in mid-summer with nearly 40 percent of the region experiencing extreme to exceptional drought.

The Southwest and Southern Plains were hardest hit by drought this year, with the southern drought centered squarely on Texas. The 2011 dry spell generally began in October of 2010 following a very wet period. Beneficial rains fell in some areas during October and November 2011, with December 2011 actually averaging wetter than normal for the state. Texas had the driest hydrologic year (October 2010-September 2011) in the 1895-2011 record, with New Mexico and Oklahoma ranking second driest and Louisiana third driest. The Rio Grande and Texas Gulf Coast river basins also had the driest hydrologic year on record. The dryness was so severe that, even with a wet December, 2011 still ranked driest on record for the calendar year (January-December) for Texas. Record heat occurred during the summer with Texas, New Mexico, Oklahoma, and Louisiana having the hottest-ever June-August and Texas experiencing record potential evapotranspiration (natural water demand). Several climate divisions in Texas, New Mexico, Oklahoma, and Louisiana, as well as Texas statewide and the Rio Grande and Texas Gulf Coast river basins, had record low values for the Palmer Hydrological Drought Index in a record that goes back 117 years.

12-month SPI map for October 2010-September 2011 Hydrologic year (October-September) precipitation, 1895-2011, for Texas

Palmer Hydrological Drought Index for Rio Grande River Basin, January 1900-December 2011 Palmer Hydrological Drought Index for Texas Gulf Coast River Basin, January 1900-December 2011

Gulf Coast to Southeast:

The Gulf Coast had drier-than-normal conditions in February, April-June, and October-December. Heavy rains from Tropical Storm Lee cut a wet swath through the middle of the Gulf Coast drought area during September. For the Southeast, March and September were wetter than normal, with January-February, April-August, and December being much drier than normal. Georgia, the epicenter of the Southeast drought, had the second driest April-August in the 1895-2011 record.

Palmer Hydrological Drought Index for August 2011 April-August precipitation, 1895-2011, for Georgia

Midwest to Upper Mississippi Valley and Northern Plains:

Minnesota statewide precipitation, August-December, 1895-2011

The Midwest/Ohio Valley was especially wet during the first half of the year. July and August were much drier than normal, with moderate-to-severe drought developing by the end of summer from Kentucky and Indiana into Iowa. Precipitation returned beginning in September, effectively ending the dry spell. The first half of the year was wet for the Upper Mississippi Valley and Northern Plains as well. Dry conditions set in beginning in August, with Minnesota having the second driest August-December on record. Moderate to severe drought spread into the area by year's end, in spite of the earlier wetness.

Far West:

Much of the West (except for the Southwest) had much-above-normal precipitation during the 2010-2011 wet season (October 2010-March 2011) and following spring and early summer. By May 31st, mountain snowpack and snow water equivalent were well above average. A drier-than-normal weather pattern dominated during the late summer and first part of the 2011-2012 wet season. Oregon had the third driest August-December, and moderate drought had spread from Oregon and Nevada into California by the end of the year.

U.S. Drought Monitor map for January 3, 2012 Oregon statewide precipitation, August-December, 1895-2011

Pacific Islands, including Hawaii:

Drought conditions in Hawaii were not as severe in 2011 as they were in 2010, but moderate to extreme drought lingered with significant long-term rainfall deficits remaining (last 12, 24, 36 months). Severely dry conditions caused by La Niña affected other Pacific islands under the jurisdiction of the United States early in 2011. The dry conditions peaked in February. Kapingamarangi was especially hard hit, with September 2010-February 2011 rainfall totalling 15 percent of normal and water conservation measures strongly encouraged at that time. Above-normal rainfall finally returned to Kapingamarangi in June 2011.

Pacific Island Percent of Normal* Precipitation
Station Name Jan 2011 Feb 2011 Mar 2011 Apr 2011 May 2011 Jun 2011 Jul 2011 Aug 2011 Sep 2011 Oct 2011 Nov 2011 Dec 2011 Jan-Dec 2011
Chuuk 76% 137% 156% 109% 66% 218% 124% 147% 120% 80% 135% 129% 123%
Guam IAP 205% 166% 138% 142% 95% 96% 195% 109% 121% 128% 75% 97% 127%
Kapingamarangi 22% 2% 61% 74% 69% 247% 199% 214% 181% 111% 92% 139% 104%
Koror 163% 145% 170% 130% 180% 129% 166% 145% 269% 107% 61% 88% 145%
Kosrae 82% 67% 51% 74% 151% 114% 76% 105% 86% 104% 82% 194% 97%
Kwajalein 119% 316% 277% 49% 91% 121% 100% 135% 101% 122% 137% 70% 121%
Majuro 100% 190% 188% 28% 109% 97% 118% 106% 108% 107% 125% 90% 110%
Pago Pago 183% 110% 52% 36% 35% 132% 40% 60% 26% 126% 143% 72% 90%
Pohnpei 98% 125% 148% 47% 95% 128% 85% 120% 97% 72% 124% 111% 102%
Saipan 182% 124% 164% 209% 154% 174% 110% 120% 64% 131% 51% 97% 116%
Yap 164% 123% 171% 129% 169% 113% 157% 133% 155% 101% 112% 106% 135%
* 1971-2000 Normals

Pacific Island Percent of Normal* Precipitation
Station Name Sept. 2010 Oct. 2010 Nov. 2010 Dec. 2010 Jan. 2011 Feb. 2011 Mar. 2011 Apr. 2011 Sep. 2010-Apr. 2011
Chuuk 114% 113% 66% 85% 76% 137% 156% 109% 105%
Guam IAP 90% 112% 53% 76% 205% 166% 138% 142% 109%
Kapingamarangi 12% 26% 25% 9% 22% 2% 61% 74% 34%
Koror 103% 89% 94% 75% 163% 145% 170% 130% 118%
Kosrae 40% 85% 74% 76% 82% 67% 51% 74% 68%
Kwajalein 71% 162% 158% 37% 119% 316% 277% 49% 127%
Majuro 166% 96% 142% 95% 100% 190% 188% 28% 121%
Pago Pago 132% 153% 82% 92% 183% 110% 52% 36% 106%
Pohnpei 100% 75% 97% 75% 98% 125% 148% 47% 93%
Saipan 67% 40% 82% 43% 182% 124% 164% 209% 84%
Yap 74% 141% 98% 69% 164% 123% 171% 129% 115%
* 1971-2000 Normals


Pre-Instrumental Perspective

Tree ring records provide a useful paleoclimatic index that extends our historical perspective of droughts centuries beyond the approximately 100-year instrumental record. Several paleoclimatic studies have shown that droughts as severe as, or worse, both in magnitude and duration, than the major 20th century droughts have occurred in the U.S. during the last thousand years. The following paleodrought report was prepared by the NOAA/NCDC Paleoclimatology and Climate Monitoring branches during 2011:


Contacts & Questions
For additional, or more localized, drought information, please visit:

Global Snow & Ice

Issued: 19 January 2012

NH Snow Cover Extent

Snow Extent data were provided by the Global Snow Laboratory, Rutgers University. Period of record is 1966-2011 (46 years).

The time series to the right shows the mean Northern Hemisphere snow cover extent for winter (December-February) from 1967 through 2011. During the three month season in 2010-2011, the Northern Hemisphere experienced its third largest snow cover extent on record at 1.98 million square km (0.76 million square miles) above the average of 45.2 million square km (17.5 million square miles). Only the winter seasons of 1977-1978 and 2009-2010 had larger snow cover extents. By the spring season (March-May), the Northern Hemisphere snow cover extent shrank to a below-average extent for the time of year. The seasonal snow cover extent was 648,000 square km (250,194 square miles) below the long-term average, and ranked as the 19th smallest (27th largest) extent on record. More information on individual global snow and ice events during 2011 can be found in the Global Hazards report.

Across North America during the 2010-2011 winter (December-February) snowfall was widespread, and the seasonal snowfall extent was the third largest on record for the continent at 0.88 million square km (340,000 square miles) above the average of 17.2 million square km (6.6 million square miles). The winter seasons of 1978-1979 and 2009-2010 both had larger snow cover extents. The above average snow cover extent for North America continued into spring (March-May), and the seasonal snow cover extent was 449,000 square km (173,300 square miles) above the long-term average and ranked as the 12th largest (34th smallest) on record. For more on information on U.S. snow/ice during 2011, please see the U.S. Snow and Ice report.

In Eurasia, snow cover extent during the 2010-2011 winter was above average. The seasonal snow cover extent anomaly of 1.1 million square km (425,000 square miles) ranks as the fourth largest on record, behind the winters of 1977-1978, 2002-2003, and 1971-1972. In contrast, the seasonal snow cover extent by spring was below average. The March-May average snow cover extent for Eurasia was 1.10 million square km (425,000 square miles) below average and ranked as the 10th smallest (36th largest) on record.

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Sea Ice Extent

March 2011 Arctic Sea ice
Daily Arctic Sea ice extent trough March, with daily
ice extents for previous low-ice-extent years.

Arctic sea ice, which is measured from passive microwave instruments onboard NOAA satellites, usually expands during the cold season to a March maximum, then contracts during the warm season to a September minimum. According to the NOAA-supported National Snow and Ice Data Center (NSIDC), the maximum Arctic sea ice extent during 2011 occurred on March 7, 2011 which is near the median date of the historical annual maximum extents. The annual maximum extent of 15.86 million square km (6.1 million square miles) was within 1 percent of the smallest annual maximum on record, which occurred in 2006. On March 7 below-average ice extent was oserved across the East Greenland Sea and Sea of Okhotsk. The March 2011 monthly average Arctic ice extent was 15.80 million km (6.1 million square miles), and ranked as the second lowest March Arctic sea ice extent in the satellite record.

September 2011 Arctic Sea ice
Arctic Sea Ice Extent on 9 September

According to the NSIDC, the minimum Arctic ice extent during 2011 occurred on September 9th, and was the second smallest on record at 4.33 million square km. The smallest ice extents on record have occurred during the past five years (2007-2011), with the smallest extent on record occurring in 2007. The average September sea ice extent was also the second smallest on record — 34.5 percent below the 1979-2000 average. During September, both the Northern Sea Route and the Northwest Passage were ice free for only the second time in recorded history; the other occurrence was in 2010. September Arctic sea ice extent has decreased at a rate of 12 percent per decade. Individually, the months of January and July set new monthly records for the smallest average sea ice extent on record. No month saw average Arctic sea ice extent above the long-term average, and the last month with above-average ice extent was May 2001.

September's PIOMAS Arctic Ice Anomaly
Sea Ice Volume Anomaly
Source: UW's Polar Ice Center

According to the Polar Science Center at the University of Washington, the second smallest extent in September was accompanied by record small sea ice volume across the Arctic. Sea ice volume takes into account both the sea ice extent and ice thickness. On September 10th the sea ice volume dropped to 4,000 cubic km (960 cubic miles), the smallest single day Arctic sea ice volume in its record. Also, the monthly averaged ice volume for September 2011 was record low at 4,200 cubic km (1,007 cubic miles) — 66 percent lower than the mean over this period and 75 percent lower than the maximum value set in 1979. The loss of multi-year ice, which tends to be thicker than newly formed sea ice is likely a contributing factor to the low sea ice volume during September 2011.

For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.

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Upper Air

During the past century, global surface temperatures have increased at a rate near 0.08°C/decade (0.14°F/decade), but this trend has increased to a rate of approximately 0.17°C/decade (0.31°F/decade) during the past 30 years. There have been two sustained periods of warming, one beginning around 1910 and ending around 1945, and the most recent beginning about 1976. Temperatures during the latter period of warming have increased at a rate comparable to the rates of warming projected to occur during the next century with continued increases of anthropogenic greenhouse gases.

Temperature measurements have also been made above the Earth's surface over the past 54 years using balloon-borne instruments (radiosondes) and for the past 33 years using satellites. These measurements support the analyses of trends and variability in the troposphere (surface to 10-16 km) and stratosphere (10-50 km above the earth's surface).

The best source of upper air in-situ measurements for studying global temperature trends above the surface is the Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC) dataset.

Data collected and averaged between the 850–300 mb levels (approximately 5,000 to 30,000 feet above the surface) indicate that 1958–2011 global temperature trends in the middle troposphere are similar to trends in surface temperature; 0.13°C/decade (0.23°F/decade) for surface and 0.15°C/decade (0.27°F/decade) for mid-troposphere. Since 1976, mid-troposphere temperatures have increased at a rate of 0.17°C/decade (0.31°F/decade). For 2011, global mid-troposphere temperatures were 0.34°C (0.61°F) above the 1971–2000 mean—the ninth warmest on record.

Since 1979, NOAA's polar orbiting satellite measurements have also been used to measure temperatures in the troposphere and stratosphere. Microwave Sounding Unit (MSU) data are analyzed for NOAA by the University of Alabama in Huntsville (UAH), Remote Sensing Systems (RSS, Santa Rosa, California) and the University of Washington (UW). These observations show that the global average temperature in the middle troposphere (the layer which is centered at an altitude of 2 to 6 miles, but which includes the lower stratosphere) has increased, though differing analysis techniques have yielded similar but different trends (see below).

In all cases these trends are positive. The analysis performed by RSS reveals a trend of 0.08°C/decade (0.15°F/decade) while the UAH analysis reveals a lower trend of 0.05°C/decade (0.09°F/decade). When adjusted by University of Washington scientists to remove the stratospheric influences from the RSS and UAH mid-troposphere average, the trends increase to 0.14°C/decade (0.25°F/decade) and 0.11°C/decade (0.20°F/decade), respectively. (A journal article is available that describes the University of Washington adjustments to remove the stratospheric influence from mid-troposphere averages.) Trends in these MSU time series are similar to the trend in global surface temperatures, which increased at a rate near 0.15°C/decade (0.28°F/decade) during the same 33-year period.

While middle tropospheric temperatures reveal an increasing trend over the last three decades, stratospheric temperatures (14 to 22 km / 9 to 14 miles above the surface) have been below average since the warming effects from the 1991 Mt. Pinatubo eruption dissipated in 1993. January-December 2011 was the 18th consecutive year with below-average temperatures (an anomaly of -0.41°C/-0.74°F), tied with 2000 as the third coolest year on record. The below-average stratospheric temperatures are consistent with the depletion of ozone in the lower stratosphere and the effects of increasing greenhouse gas concentrations. The large temperature increase in 1982 is attributed to the volcanic eruption of El Chichon, and the increase in 1991 was associated with the eruption of Mt. Pinatubo in the Philippines.

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200-2011 Annual Wildfire Counts
2000–2011 U.S. Wildfire Counts
Data Source: NIFC

Issued: 19 January 2012

During 2011, drier-than-average conditions were observed from the western states across the southern tier of the country and into the Southeast. The driest area of the country was the Southern Plains of Oklahoma, Texas, and New Mexico. These regions also experienced warmer-than-average conditions during 2011. The Western Great Lakes were also drier than normal during the latter half of the year, but areas across the Northern Plains, Ohio Valley, and Northeast were wetter than normal for the annual period. Many locations across the Ohio Valley and Northeast had their wettest year on record. The overall pattern during 2011 created ideal wildfire conditions across most of the southern U.S. during the year and the driest areas of the Southern Plains experienced above average wildfire activity. New Mexico, Texas, Arizona, and Minnesota all had record-breaking wildfires during 2011.

Year-to-Date Wildfire Statistics*
January–December Totals Rank
(out of 12 years)
Record 2000-2010
Value Year
Acres Burned 8,711,367 3ʳᵈ Most 9,873,745 2006 6,612,363
10ᵗʰ Least
Number of Fires 74,126 7ᵗʰ Most 96,385 2006 77,951
6ᵗʰ Least
Acres Burned per Fire 117.5 3ʳᵈ Most 130.2 2005 85.2
10ᵗʰ Least

*Data Source: The National Interagency Fire Center (NIFC)

Through December 30th, the nationwide number of fires year-to-date was 73,484 which burned 8.7 million acres (3.5 million hectares), with an average of 119 acres (48.2 hectares) per fire. The spring and summer were particularly active wildfire periods, while the fall season was quieter than average. The fires across the southern U.S. led 2011 to having the third most active wildfire season with respect to acres burned and sixth least active in terms of number of fires. Texas had the most acres burned of any state during the year, with over 3.7 million acres (1.5 million hectares) burned across the state during 2011, 43 percent of the national total. Several of the large fires were destructive and expensive to control, with the state of Texas spending over a million dollars a day to control the fires during the very active spring period. During 2011 the damages from wildfires across the U.S. will exceed one billion U.S. dollars.

The spring wildfire season (March-May) was particularly noteworthy. During the three month period, 20,100 fires burned over 3.2 million acres (1.3 million hectares) across the U.S., mostly across Texas, Arizona, and New Mexico. The acres burned were record high for the 3-month period, surpassing the spring of 2008 when 1.5 million acres (607,000 hectares) burned nationwide. Wet conditions during the 2010 summer caused an abundance of vegetative growth across the Southern Plains. The region then experienced a very dry winter and spring season, causing the new vegetation to dry, creating a significant source of wildfire fuels. During the January 1st through April 30th period, 2.2 million acres (0.9 million hectares) burned across Texas alone. Several fires during the season affected populated areas in Texas, including the Wildcat Fire which forced an evacuation in San Angelo, Texas, and the Rock House Fire, which burned over 40 homes in Fort Davis.

Number of Fires and Acres burned during 2011
Acres burned during 2011
Compared to 2001–2010 Average
Number of Fires and Acres burned during 2011
Number of fires during 2011
Compared to 2001–2010 Average

Significant Events during 2011

The Las Conchas Fire burned in northern New Mexico during June and July. The fire consumed over 156,500 acres (63,000 hectares). This fire surpassed the Dry Lakes Fire of 2003 as New Mexico’s largest wildfire on record. The fire was driven by strong winds and extremely dry fuels. The largest concern of the firefighters was the town of Los Alamos, home to the country’s premier nuclear research facility. The fire encroached upon the grounds of the research facility several times, but fire crews were able to keep the flames from spreading. According to media reports, the blaze was said to be as close as 50 ft away from the grounds of the lab, raising fears it could reach a cache of 30,000 drums, each containing 55 gallons of plutonium-contaminated waste. This prompted the Environmental Protection Agency to deploy air monitors and aircraft to monitor radiation levels. The lab, as well as the Bandelier National Monument, was closed and several cities nearby including Los Alamos, Cochiti Mesa, and Las Conchas were evacuated as a precaution. Over 1,200 crews from around the country were called in to battle the blaze.

Wallow Fire Smoke 7 June 2011

Satellite image of Wallow Fire 7 June 2011
Source: NASA

During May and June, the Wallow Fire ravaged over 538,000 acres (217,700 hectares) across Arizona. The Wallow fire was the largest fire ever reported in the state of Arizona, surpassing the Rodeo-Chediski Fire by nearly 70,000 acres (28,328 hectares), which occurred in July 2002. The fire threatened several communities in eastern Arizona, forcing the evacuation of Sunrise, Greer, Blue River, Alpine, Nutrioso, Eager, and Springerville. The fire had far reaching impacts beyond Arizona, with the strong winds blowing the smoke as far away as the Great Lakes, creating poor air quality conditions from Arizona to Wisconsin.

Satellite image of Texas Fires 6 September 2011

Satellite image of Texas Fires 6 September 2011
Source: NASA

During the first week of September, the Bastrop fire raged in central Texas. As Tropical Storm Lee made landfall along the Louisiana coast, the storm caused strong winds to whip up across Texas. The strong winds, combined with the ongoing drought, created ideal wildfire conditions. The Bastrop fire was ignited on September 4th, just east of Austin, Texas. The fire burned rapidly out of control. By the end of the month, the fire had burned over 34,000 acres (13,800 hectares) and destroyed over 1,600 homes. According to media reports, the fire broke the record for the number of homes lost due to a single fire in Texas history.

Satellite image of Pagami Creek Fire 12 September 2011

Satellite image of Pagami Creek Fire
12 September 2011
Source: NASA

The Pagami Creek fire burned approximately 93,000 acres (37,600 hectares) in the Superior National Forest in northern Minnesota during September and October. The fire was ignited on August 18th by a lightning strike. The fire was not initially suppressed to allow natural processes to take place in the forest. The fire had grown to only 13 acres (5 hectares) by September 12th. But after the 12th, strong winds and dry conditions caused the fire to grow rapidly out of control. The acreage burned is the tenth most by a single fire in Minnesota history, and the largest fire to affect the state since the Cloquet-Moose Lake Fire in 1918. By the end of September over 5.7 million dollars had been spent to control the wildfire.

Citing This Report

NOAA National Climatic Data Center, State of the Climate for Annual 2011, published online December 2011, retrieved on April 27, 2015 from http://www.ncdc.noaa.gov/sotc/2011/13.