National Overview - Annual 2015


NCEI 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 13, 2016: This temperature and precipitation analysis is based on data back to 1895, resulting in 121 years of data. Data for 2015 should be considered preliminary. The most up-to-date temperature and precipitation data is available through Climate at a Glance.

Supplemental 2015 Information


National Temperature and Precipitation Analysis


In 2015, the contiguous United States (CONUS) average temperature was 54.4°F, 2.4°F above the 20th century average. This was the second warmest year in the 121-year period of record for the CONUS. The warmest year on record was 2012 when the annual average temperature was 55.3°F. This marks the 19th consecutive year that the annual average temperature for the CONUS was above the 20th century average. The last year with a below-average temperature was 1996. Since 1895, when the national temperature records began, the CONUS has observed an average temperature increase of 0.14°F per decade.

Precipitation averaged across the CONUS in 2015 was 34.47 inches, 4.53 inches above the 20th century average. This was the third wettest year on record. Only 1973 and 1983 were wetter. During both 1973 and 1983 strong El Niño conditions were present in the equatorial Pacific Ocean, similar to 2015. Over the 121-year period of record, precipitation across the CONUS has increased at an average rate of 0.16 inch per decade.

The year started out with record and near-record warmth across most of the West, and record and near-record cold in the Midwest and Northeast. The early-year warmth in the West as accompanied by below-average precipitation and record low mountain snow packs, contributing to crippling summer drought and a record-breaking wildfire season in the region. Beneficial precipitation began to fall across the region by the end of the year, consistent with the strong El Niño that developed during 2015. In the East, the early-year cold was accompanied by heavy snowfall for some locations, including Boston, Massachusetts, which set a new seasonal snowfall record with 110.6 inches of snow. By the end of the year, that pattern had flipped, with record and near-record temperatures across most of the East and near- to below-average temperatures for much of the West, associated with much needed above average precipitation across the region. However, long-term precipitation deficits and drought conditions continued to plague most of California by the end of the year. During most of 2015, starting in the spring, record and near-record precipitation was observed across parts of the central CONUS, helping to end multi-year drought conditions in the Southern Plains and contributing to record breaking flooding. During the course of 2015, the CONUS drought footprint shrank about 10 percent. The coverage of extreme precipitation totals and warm temperatures contributed to the fourth highest U.S. Climate Extremes Index in the 106-year record for the CONUS.

On a statewide and seasonal level, 2015 was a year of temperature and precipitation extremes. Every state had an annual temperature that was above average and ranked in at least the warmest third of the historical record. In the West and Southeast, twenty-eight states, including Alaska, had an average temperature that was much above average, or falling in the warmest third of the historical record. Florida, Montana, Oregon and Washington were each record warm. Alaska, California, and Idaho had their second warmest year. Most of the central and southeastern U.S. were wetter than average for 2015, including 14 states that were much wetter than average. Oklahoma and Texas were record wet for the year, with both states becoming drought free for the first time since 2010. Parts of the Northeast and West were drier than average. Connecticut had its fourth driest year. In California, year-end precipitation helped erase early-year deficits, resulting in the state's 13th driest year.

Seasonal highlights in 2015 included:

  • The CONUS had its 20th warmest winter on record. The season was marked by early-season near-record warmth and late-season cold. Around mid-January, a pattern shift in the East resulted in a warmer than average start to the month and a below average end to the month. The below-average temperatures in the East continued through February and into early spring. February brought a stark spatial contrast in temperatures across the nation. The West was much warmer than average with several states being record warm. Much-below-average temperatures spanned the East with nine states having their second coldest February on record. Several cities in the Northeast had their coldest month of any month on record in February. The CONUS winter precipitation total was slightly below average. In the West, despite near-average to below-average winter precipitation totals, the record warmth caused most of the precipitation to fall as rain and not snow, which had implications on summer drought intensification and water resource crisis during the warm months due to low snowpack. Record seasonal snowfall totals were observed in parts of the Northeast and Midwest.
  • The national spring temperature of 53.2°F was 2.2°F above the 20th century average and the 11th warmest on record. Above-average spring temperatures were observed in the West, Midwest, and Southeast, with Florida being record warm. The season started out near-record cold for parts of the Northeast, but turned record and near-record warm by May. The March-May precipitation total for the contiguous U.S. was 9.40 inches, 1.46 inches above the 20th century average. This was the 10th wettest spring and wettest since 2011. Above-average precipitation was observed across the Central and Southern Plains and Lower Mississippi Valley. Most of the spring precipitation fell during May, which was the wettest month, of any month, on record for the CONUS. Record-breaking precipitation fell across the Southern and Central Plains and Southern Rockies, ending drought conditions that began in 2010 in Oklahoma and Texas. Despite the above-average precipitation, the warm spring temperatures contributed to the smallest spring snow cover extent on record for the CONUS.
  • The average CONUS summer temperature was 72.8°F, 1.4°F above the 20th century average, the 12th warmest on record. Much of the CONUS was warmer than average during summer, especially both coasts. California, Oregon, and Washington each had their warmest summer on record. June was particularly warm for the CONUS, with a temperature 2.9°F above average, the second warmest June on record. The CONUS precipitation total for summer was 9.19 inches, 0.87 inch above average and the 16th wettest on record. In June, the remnants of Tropical Storm Bill brought record breaking precipitation to the Mid-Mississippi and Ohio Valleys. July was also record wet for much of the Ohio Valley, with significant flooding observed. Outside of the CONUS, drought conditions rapidly expanded in Puerto Rico during the late spring and summer, but improved in Hawaii with the remnants of several tropical cyclones impacting the islands, bringing record-breaking summer rains.
  • The average autumn temperature for the Lower 48 was 56.8°F, 3.3°F above the 20th century average. This was the warmest autumn on record for the CONUS, surpassing the previous record set in 1963. Every state across the nation had an above-average autumn temperature, with 41 states being much warmer than average. The CONUS autumn precipitation total was 8.38 inches, 1.50 inches above average, ranking as the 15th wettest and wettest since 2009. South Carolina had its wettest autumn on record with 23.76 inches of rain, 13.91 inches above average. Most of the South Carolina rain fell in early October when moisture associated with Hurricane Joaquin offshore interacted with an upper level low, dousing the region. Separately, heavy rain associated with remnant tropical cyclones from the East Pacific impacted Texas, causing significant flooding across the state.
  • December ended the year on a record warm and wet note. The CONUS December temperature was 6.0°F above average. This broke the previous record set in 1939 by 1.0°F. Record warmth engulfed the eastern half of the nation, where 29 states had the warmest December on record. The December precipitation total for the contiguous U.S. was 3.93 inches, 1.58 inches above the 20th century average, ranking as the wettest December on record. This surpassed the previous record of 3.76 inches set in 1982. This is the only month in the 121-year period of record that has both the title of warmest and wettest month. Much of the central U.S. was record and near-record wet. A strong storm in late December across the central CONUS caused record flooding, severe weather, and heavy snowfall resulting in over 50 fatalities, the deadliest weather event of 2015.

This annual report places the temperature and precipitation averages into historical perspective, while summarizing the notable events that occurred in 2015. More detailed analysis on individual months can be found through the Climate Monitoring home page.


Seasonal Analysis


Winter

The winter of 2014/15 was warmer than average for the contiguous U.S. with a temperature of 34.3°F, 2.1°F above the 20th century average. This was the 20th warmest winter on record for the Lower 48. The season consisted of the third warmest December, 21st warmest January, and a slightly cooler than average February. The winter started warmer than average with the December temperature 4.1°F above average, the warmest December since 1957. Around mid-January, a pattern shift in the East resulted in a warmer than average start to the month and a below average end to the month. The below-average temperatures in the East continued through February and into early spring. Eleven states across the West were much warmer than average for the December-February period, with Arizona, California, Nevada, Oregon, Utah, and Washington being record warm. Cooler-than-average conditions were widespread across the East. During December, every state had an above-average temperature. In January, much of the contiguous U.S. had near-average temperatures, with the West being much warmer than average. February brought a stark contrast in temperatures across the nation. The West was much warmer than average with Arizona, California, Oregon, and Washington being record warm. Much-below-average temperatures spanned the East with nine states in the Midwest and Northeast having their second coldest February on record. Several cities in the Northeast had their coldest month of any month on record in February including Buffalo, New York where the monthly average temperature was 10.9°F, dipping below the 11.6°F observed in February 1934. Several additional cities, including Chicago, Illinois and Cleveland, Ohio observed their coldest February on record.

The 3-month average CONUS precipitation of 6.15 inches was 0.64 inch below average and the 29th driest on record. December had near-average precipitation while January and February were drier than average. For the season, parts of the West, Midwest, and Mississippi Valley were drier than average, while parts of the Southwest and Northeast were wetter than average. Despite a near-average winter precipitation total for California, Oregon, and Washington, the record warmth caused most of the precipitation to fall as rain and not snow, which had implications on the drought intensification and water resource crisis during the warm months. The region is highly dependent on spring snowmelt to refill reservoirs and replenish ground water.

According to NOAA data analyzed by the Rutgers Global Snow Lab, for the winter season, the contiguous U.S. snow cover extent was 62,000 square miles below the 1981-2010 average; this was the 23rd largest (27th smallest) winter snow cover extent for the contiguous U.S. and the smallest since the winter of 2011/12. Much below average snowfall and snowpack was observed across the West, which exacerbated the drought and wildfire season during summer and autumn. Snowpack totals at the end of the snow season across the West were record low for many locations in the Sierra Nevada Mountains and Cascades. Seasonal snowfall totals were generally above average in the East, especially the Midwest and Northeast. An active coastal storm track and below-average temperatures were associated with a record snow season in Boston, Massachusetts. Boston received 110.6 inches of snow during the snow season, surpassing the record of 107.6 inches set in 1995/96. Most of the snow during the season fell during late winter and early spring, with snow remaining on the ground in some places until June.

At the beginning of winter, 28.7 percent of the CONUS was in drought and by the end of the season the drought footprint expanded to 31.2 percent of the CONUS. Drought conditions worsened in the Northwest, Central Rockies, and parts of the Southern Plains and South Florida, while drought improved in parts of the Southwest and Northern California.

Spring

The national spring temperature of 53.2°F was 2.2°F above the 20th century average and the 11th warmest on record. This was the warmest spring since the record breaking spring of 2012. Above-average spring temperatures were observed in the West, Midwest, and Southeast. Florida had its warmest spring on record with a temperature 4.6°F above average. The Northeast and Southern Plains had near-average spring temperatures. March was the 12th warmest on record for the contiguous U.S. with above average temperatures across the western half of the nation and Southeast. Below-average temperatures dominated New England, where four states were much cooler than average. April was the 16th warmest on record. Much of the nation had slightly warmer than average conditions, with Florida being record warm and the Northeast and West Coast being near-average. May had a near-average temperature. The East Coast was much warmer than average with Connecticut, New Hampshire, Massachusetts, and Rhode Island being record warm, in contrast to late winter and early spring. The Northwest was also warmer than average with below-average temperatures across the central United States.

The March-May precipitation total for the contiguous U.S. was 9.40 inches, 1.46 inches above the 20th century average. This was the 10th wettest spring and wettest since 2011. Below-average precipitation was observed along both coasts where six states had a much drier than average season. Above-average precipitation was observed across the central U.S. with six states in the Central and Southern Plains and Lower Mississippi Valley being wetter than average. Texas had its wettest spring on record with 223 percent of average precipitation. March was drier than average for the CONUS, with below-average precipitation across a large area of the nation — from the West Coast, through the Rockies and Great Plains, and into the Midwest and Northeast. Above-average precipitation was observed in the Southern Plains and Lower Mississippi Valley. April was wetter than average for the nation. The northern tier was drier than average, while much of the southern tier was wetter than average.

The May precipitation total for the nation was 4.44 inches, 1.53 inches above average. This was not only the wettest May on record for the country, surpassing the previous record of 4.24 inches in 1957, it was the wettest month of any month, surpassing the 4.29 inches that fell in October 2009. Colorado, Oklahoma, Texas, and Utah were each record wet for the month with ten additional states being much wetter than average. Despite the record wet month for the CONUS, drier than average conditions prevailed along the East Coast where seven states were much drier than average. However, in the Southern Plains, the heavy precipitation helped to end multi-year drought conditions. Oklahoma and Texas both had their wettest month of any month on record, nearly erasing drought for the first time since 2010 in those states. Although long-term (60+ months) precipitation deficits persisted in some locations, some reservoirs returned to above-average levels after being record and near-record low for the past several years.

Tropical Storm Ana made landfall near Myrtle Beach, South Carolina on May 10 th bringing heavy rain to the Carolinas, but reported damage was minimal.

At the beginning of the season, 31.9 percent of the CONUS was in drought and by the beginning of June only 24.6 percent was in drought. Drought dramatically improved across the Southern and Central Plains. Drought also improved along parts of the Gulf Coast and Upper Midwest. However, drought conditions expanded and intensified in parts of the Northwest due to lack of snowpack from the winter and spring seasons and in the Northeast.

In terms of snow, for the spring season (March-May), the contiguous U.S. snow cover extent was 362,300 square miles below the 1981-2010 average. This was the smallest spring snow cover extent in the 49-year period of record. The previous record low spring snow cover extent occurred in 1968. Snow cover was much below average during March, April, and May, with monthly rankings of fifth smallest, ninth smallest, and 18th smallest, respectively. During each month, much below-average snow cover was observed across the western half of the nation, with above-average snow cover in parts of the Midwest and Northeast.

Summer

The average CONUS summer temperature was 72.8°F, 1.4°F above the 20th century average, the 12th warmest on record. Much of the CONUS was warmer than average during summer, especially both coasts. In the West, seven states were much warmer than average, including California, Oregon, and Washington, which each had their warmest summer on record. Along the East and Gulf Coasts four states were much warmer than average. Below- to near-average temperatures were observed in the Central Plains, Midwest, and parts of the Northeast.

June was the second warmest on record with an average temperature of 71.4°F, 2.9°F above average; only June 1933 was warmer. The West and Southeast were much warmer than average, where 14 states had a much above average June temperature. Five western states were record warm. Several western cities set new all-time June temperature records, due in part to an intense heatwave the second half of the month, including Boise, Idaho where the temperature soared to 110°F. Below-average June temperatures were observed in the Midwest and Northeast. The July national temperature was near average. The Northwest, South, and Northeast were warmer than average, while central regions of the country were cooler than average, from the Rockies to Midwest. Several cities in the Northwest had a record or near-record warm July. The average temperature in Seattle, Washington was 71.2°F, 5.5°F above normal, marking the warmest July on record for the city. August was 0.9°F warmer than the 20th century average for the CONUS and ranked in the warmest third of the historical record. Above-average temperatures spanned the West and Northeast, while the central CONUS was cooler than average. Several locations in both the Northwest and Northeast were record warm for August, including JFK airport in New York City, New York; Caribou, Maine; Rome, Oregon; and Crescent City, California. Much of Hawaii was also record warm during August, Hilo (79.7°F) and Kahului (82.9°F) experienced their warmest month, of any month, on record. Through September 5th, Kahului had experienced 52 days with the maximum temperature reaching 90°F. This bested the previous record of 49 days set in 1996.

The CONUS precipitation total for summer was 9.19 inches, 0.87 inch above average and the 16th wettest on record. Above-average summer precipitation was observed across the Southwest, Midwest, and Northeast. In the Midwest and Northeast, eight states were much wetter than average. Below-average summer precipitation fell across the Northwest and Southeast. For June, the CONUS precipitation total was 121 percent of average and the ninth wettest on record. Above-average precipitation was observed across the Southwest, Southern Plains, Midwest, and Northeast. Illinois, Indiana, and Ohio were record wet with 12 additional states being much wetter than average. A significant portion of the precipitation that fell across those regions was associated with the remnants of Tropical Storm Bill that made landfall in Texas on June 16th. Below-average precipitation fell across the Northwest were three states were much drier than average. The July CONUS precipitation total was the 12th wettest on record with a precipitation total 116 percent of average. Above-average precipitation fell across much of the West, Great Plains, and Ohio Valley. Kentucky had its wettest July on record with 9.37 inches of precipitation, 5.03 inches above average. Significant flooding was observed across the state. Below-average precipitation was observed in the Northwest, Great Lakes, and Southeast. The August CONUS precipitation total was slightly below average and ranked in the driest third of the historical record. Most of the nation had near- to below-average precipitation during the month.

During the season the CONUS drought footprint expanded from 24.6 percent to 30.4 percent. Drought conditions worsened across the Northwest, Southern Plains and Lower Mississippi Valley, and the Southeast. The hot and dry weather in the Southern Plains and Lower Mississippi Valley caused an intense short-term drought to develop despite long-term drought being eliminated earlier in the year from heavy spring precipitation. Drought improved in parts of the Southwest and Northeast.

Outside of the contiguous U.S. drought conditions during the summer rapidly expanded in Puerto Rico during the late spring and summer. In late-May about 17 percent of Puerto Rico was in drought, but by the end of the summer the drought footprint expanded to 63.8 percent of the island. At the end of summer 24.9 percent of Puerto Rico was in Extreme Drought (D3), mostly across the eastern half of the island. Drought conditions are typical during the summer and autumn in Puerto when an El Niño is present. In Hawaii, heavy rain associated with the remnants of three tropical cyclones, Hilda, Kilo, and Ignacio, resulted in Honolulu receiving 7.63 inches of rain during August, more than twice the previous record that occurred in 2004. The normal August precipitation total for Honolulu is 0.56 inch.

Fall

The average autumn temperature for the Lower 48 was 56.8°F, 3.3°F above the 20th century average. This was the warmest autumn on record for the CONUS, surpassing the previous record set in 1963. Every state across the nation had an above-average autumn temperature, with 41 states being much warmer than average. Florida tied its warmest autumn on record with a temperature 3.6°F above average.

The September average temperature was 68.6°F, 3.7°F above average and the second warmest on record behind only 1998. Much of the CONUS was warmer than average, with the exception of the Northwest and Southeast. Thirty states had September temperatures that were much above average and nine states—Connecticut, Colorado, Maine, Michigan, Minnesota, New Mexico, Rhode Island, Utah, and Wisconsin—were record warm. The October average temperature was 57.2°F, 3.1°F above average and fourth warmest on record and warmest since 1963. The western two-thirds of the nation was warmer than average with 14 states being much warmer than average, including Washington which was record warm. Below-average temperatures were observed in parts of the Northeast. The November average temperature was 3.0°F above the 20th century average and ranked among the warmest third of the historical record. In a reversal of pattern from October, the West was cooler than average while the East was much warmer than average. New Jersey tied its warmest November on record; in addition, 31 other states were much warmer than average.

The CONUS autumn precipitation total was 8.38 inches, 1.50 inches above average, ranking as the 15th wettest and wettest since 2009. Above-average precipitation was observed across the Great Basin, Southern Plains, Midwest, and Southeast. Six states were much wetter than average. South Carolina had its wettest autumn on record with 23.76 inches of rain, 13.91 inches above average, besting the previous record wet autumn of 1959 by 5.34 inches. Below-average autumn precipitation was observed in the West and Northeast.

The September CONUS precipitation total was 2.11 inches, 0.37 inch below average, ranking in the driest third of the historical record. Above-average precipitation was observed in the Northeast and Midwest, while the southern U.S. was drier than average. The October precipitation total was 135 percent of average and the 13th wettest on record. Above-average precipitation spanned the southern United States. The heaviest rain was observed across South Carolina. Moisture from Hurricane Joaquin, offshore, interacted with an upper level trough to bring rainfall totals exceeding two feet to some locations during the first week of the month. Record flooding was observed in South Carolina and parts of North Carolina with numerous dam failures and road closures. South Carolina had its wettest October on record with over four times its average monthly precipitation. Separately, heavy rain associated with remnant tropical cyclones from the East Pacific impacted Texas, causing significant flooding and drought relief across the state. Texas had its second wettest October on record with over twice its average monthly rainfall. The November CONUS precipitation total was 3.35 inches, 1.12 inches above average and the fourth wettest on record. Above-average November precipitation was observed across much of the Great Plains, Midwest, and Southeast. Beneficial precipitation also fell across western areas of Washington State. Eleven states were much wetter than average in these regions. Arkansas and Missouri were record wet. The Arkansas precipitation total was 10.76 inches, 6.47 inches above average. The Missouri precipitation total was 7.89 inches, 4.98 inches above average. Below-average precipitation fell across the Northeast. New York and Vermont were much drier than average.

During the entire season, the CONUS drought footprint shrank from 30.4 percent to 20.6 percent. Drought improved across the Southern Plains and Lower Mississippi Valley where moisture from East Pacific tropical cyclones doused the region. Drought also improved in the Southeast and coastal Northeast.

For information on December, please see our December 2015 report.

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Alaska Annual Summary

The average statewide temperature for Alaska during 2015 was 30.1°F, 4.1°F above average. This tied 2002 as the second warmest year on record for Alaska in a period of record that dates back to 1925. The warmest year on record for Alaska occurred just last year with an average temperature of 30.3°F. The Alaska annual temperature is increasing at an average rate of 0.2°F per decade. Much of central and northern Alaska had much above average temperatures during 2015, while the Aleutians and parts of southern Alaska, including the panhandle were record warm, The 2014/15 winter temperature across Alaska was 11.6°F, 8.0°F above average. This was the fourth warmest winter for the state and the warmest since 2003. Spring was also the fourth warmest on record with a statewide average temperature that was 5.7°F above average. The summer average temperature was 52.0°F, 1.5°F above average and the 13th warmest on record. Autumn was the 15th warmest on record with a temperature of 29.3°F, 3.4°F above average. The year ended with a warmer than average December, with a statewide average temperature of 7.7°F, 4.0°F above average.

The Alaska annual precipitation total was 40.10 inches, 3.40 inches above average. This was the 15th wettest year for Alaska. The wettest year on record for Alaska occurred in 1928 with 43.54 inches of precipitation. Northern and western parts of Alaska had near-average annual precipitation totals, while the eastern and central parts of the state were wetter and much wetter than average. The annual precipitation total for Alaska is slightly decreasing at an average rate of 0.03 inch per decade. The Alaska winter precipitation total was 7.85 inches, 0.30 inch below average, and ranked near the median value in the 1925-2015 record. Much of the precipitation that fell across the state during the season was rain and not snow, with much below average snowpack at the end of the season. The spring precipitation total was 6.81 inches, 0.58 inch above average and the 26th wettest on record. The summer precipitation total was 10.87 inches, 0.87 inch above average, also the 26th wettest on record. Above-average precipitation fell across eastern parts of the state, but below-average precipitation across western and central parts of the state resulted in drought expanding during the season. In mid-July the drought footprint peaked at 20.6 percent of the state in drought. Late-summer and autumn precipitation helped to alleviate drought later in the year. The autumn precipitation total was 15.76 inches, 3.41 inches above average, the sixth wettest on record. December rounded out the year with a precipitation total of 1.65 inches, 1.42 inch below average, the fourth driest such month on record.


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 was "very wet/very dry". The figures above depict 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". The "very warm" categories translate to the "much above average" while the "very cold" categories translate to the "much below average" in terms of the NCDC ranking methods. This is similar for the "very wet" and "very dry" categories and the NCDC ranking methods of precipitation totals.

The table below shows the percent area of the nation "very warm" and "very cold" for each month of 2015.

Month Percent area of CONUS "very warm" Percent area of CONUS "very cold"
January 25.90 0.00
February 29.8731.42
March 46.502.22
April 8.170.00
May 16.102.01
June 39.771.10
July 13.135.04
August 23.390.00
September 61.210.00
October 38.860.00
November 46.130.22
December 51.170.00

The table below shows the percent area of the nation "very wet" and "very dry" for each month of 2015.

Month Percent area of CONUS "very wet" Percent area of CONUS "very dry"
January 6.378.36
February 2.744.46
March 6.1026.72
April 10.83 2.21
May 44.826.77
June 18.177.63
July 24.852.84
August 3.703.36
September 1.436.69
October 20.590.52
November 29.711.31
December 36.120.00

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Climate Extremes Index

The U.S. Climate Extremes Index (USCEI) for 2015 was 70 percent above average, ranking as the fourth highest annual USCEI in the 106-year record and highest since 2012. When excluding the tropical cyclone component, the USCEI was even higher at 105 percent above average, the second highest value on record behind only 1998. The national components of the USCEI that were much above average for the year included extremes in warm maximum (eighth highest) and minimum temperatures (third highest), one-day precipitation totals (second highest) and days with precipitation (fifth highest). Regionally, the CEI was much above average for the Northern Rockies and Plains (elevated extremes in warm maximum and minimum temperatures and days with precipitation), South (elevated extremes in warm minimum temperatures, spatial extent of wet conditions, one-day precipitation totals, and days with precipitation), Southwest (elevated extremes in warm maximum and minimum temperatures and days with precipitation), Northwest (elevated extremes in warm maximum and minimum temperatures, spatial extent of drought, and one-day precipitation totals), and West (elevated extremes in warm maximum and minimum temperatures and spatial extent of drought). In fact the Northwest had its highest annual CEI on record and the West had its second highest.

Winter 2015 Regional CEI Map
Regional CEI values for winter 2014/14

The winter (Dec-Feb) USCEI was 15 percent above average. Elements that contributed to the above-average seasonal USCE were warm maximum and minimum temperatures, particularly in the West, and one-day precipitation totals. The West had its highest CEI on record for the season, due to warm maximum and minimum temperatures and days without precipitation. The CEI was also much above average in the Southwest and Northwest. The South and Ohio Valley had their lowest winter CEI values on record.

Spring 2015 Regional CEI Map
Regional CEI values for spring 2015

The spring (Mar-May) USCEI was 10 percent below average and the lowest spring USCEI since 2009. On the regional scale, the CEI was above average in the West and Northwest due to extremes in warm maximum and minimum temperatures and the spatial extent of drought. The CEI was below average in the Southwest, Ohio Valley, and Northeast, and much below average in the Upper Midwest.

Summer 2015 Regional CEI Map
Regional CEI values for summer 2015

The summer (June-August) USCEI was 10 percent above average, ranking near the median value in the 1910-2015 period of record. Regionally, CEI was much above average in the West and Northwest, due to elevated components of warm maximum and minimum temperatures, spatial extent of drought and days with precipitation. The summer CEI was above average in the Southwest, South, and Ohio Valley, but below average in the Upper Midwest and Northeast.

Summer 2015 Regional CEI Map
Regional CEI values for autumn 2015

The autumn (Sep-Nov) USCEI was 50 percent above average — the 10th highest on record and highest since 2004. Nationally, the components that measure extremes in warm maximum and minimum temperature and one-day precipitation totals were much above average. In fact, the warm minimum temperature component was 590 percent above average, marking the largest warm minimum temperature component on record for autumn or any season (winter, spring, summer, autumn) on record. Each region had an above-average CEI for the season with warm maximum and minimum temperatures being the largest contributing factor. No region had its highest autumn CEI on record, but much-above average seasonal CEI values were observed in the Northwest, Northern Rockies and Plains, South, Upper Midwest, Ohio Valley, and Northeast.


National Snow and Ice

The 2014/15 winter season (December 2014-February 2015) was marked by much warmer than average conditions during the first half of the season and cooler than average conditions the second half. February was extremely cold across the eastern half of the contiguous U.S. with 29 states being much cooler than average, while the West was extremely warm with eight states being much warmer than average. For the season as a whole, 11 states in the West were much warmer than average, including six states being record warm. The record and near-record warmth in the West was associated with much below-average snow cover and snowpack during the season, while the cold end to winter brought above average snowfall to much of the Midwest and Northeast. This pattern, of a warm West and cool East, continued into early spring. The cold late-winter and early-spring temperatures combined with an active storm pattern brought a tremendous amount of snowfall to coastal New England. Boston, Massachusetts received 110.6 inches of snow during the snow season, surpassing the record of 107.6 inches in 1995-96. Most of the snow during the season fell during late winter and early spring, with snow remaining on the ground in some places until June.

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

According to NOAA data analyzed by the Rutgers Global Snow Lab, for the winter season, the contiguous U.S. snow cover extent was 62,000 square miles below the 1981-2010 average; this was the 23rd largest (27th smallest) winter snow cover extent for the contiguous U.S. and the smallest since the winter of 2011/12. The heavy late-season snow in the East was not enough to compensate for the lack of snow in the West. On the monthly scale, the December and January snow cover extents were below average, while the February snow cover extent was above average. For the spring season (March-May), the contiguous U.S. snow cover extent was 362,300 square miles below the 1981-2010 average. This was the smallest spring snow cover extent in the 49-year period of record. The previous record low spring snow cover extent occurred in 1968. Snow cover was much below average during March, April, and May, with monthly rankings of fifth smallest, ninth smallest, and 18th smallest, respectively. During each month, much below-average snow cover was observed across the western half of the nation, with above-average snow cover in parts of the Midwest and Northeast.

In Alaska, the snow cover extent was mixed during the winter and spring. Early in the winter, snow cover extent was above average, but warm and dry conditions limited snow cover from February to May. The December and January snow cover extent for the state was slightly above average. By February, the snow cover extent was below average, which continued into early summer. The snow cover extent from April through June was among the five smallest for each month and was record small for June. A warm spring limited the amount of frozen precipitation that fell across the state during the second half of the season. The lack of snow in southern Alaska prompted the move of the iconic Iditarod race over 200 miles northward. This was only the second time the race had to be moved northward due to lack of snow, with the first being in 2003.

Western US Snowpack 1 May 2015
Western U.S. Snowpack
April 1, 2015
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 highly dependent on the amount of snow melt that will occur in spring and is proportional to the amount of snow on the ground. The annual snow pack typically peaks in early April. As of April 1st, most locations from the Great Basin to the West Coast had much below-average snow pack. In the Cascade and Sierra Nevada Mountains, snow pack totals were less than 25 percent of normal and record low for several locations. For parts of California, this marks the fourth consecutive spring with much below average snow pack, causing significant concerns for water resources going into the warm and dry season. Please visit our supplemental page for additional information on April 1st snow water equivalents across the region. Snow pack was also less than 25 percent of normal for much of the Great Basin and southern Rockies. Near-average snow pack was observed in the Central and Northern Rockies. In Alaska, snow pack totals less than 25 percent of average were observed across southern regions of the state, while interior locations had near-average snow pack.

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Hurricanes and Tropical Storms

The 2015 North Atlantic hurricane season had eleven tropical storms, four hurricanes, and two major hurricanes. The number of tropical storms was below the 1981-2010 average of 12.1; the number of hurricanes was below the 1981-2010 average of 6.4; and the number of major hurricanes was near the 1981-2010 average of 2.7. The number of tropical cyclones was more than the eight that occurred during the 2014 season. When El Niño conditions are present in the equatorial Pacific like in 2015, tropical cyclone activity across the North Atlantic basin tends to be suppressed due to increased wind shear, an unfavorable condition for tropical cyclone development.

Two tropical storms, Ana and Bill, made landfall in the contiguous U.S. during the season. The largest impacts of both of these systems were heavy rain across the Carolinas when Ana made landfall in May and heavy rain across the Southern Plains and Midwest when Bill made landfall in June. No hurricanes or major hurricanes made landfall. The 2015 hurricane season marks a continuation of a record-long streak of no major hurricanes (Category 3 or stronger) making landfall in the United States. The last major hurricane to make landfall in the U.S. was Wilma on November 24, 2005. This major hurricane drought surpassed the length of the eight-years from 1861-1868 when no major hurricane struck the United States' coast. On average, a major hurricane makes landfall in the U.S. about once every three years. Even through Major Hurricane Joaquin did not make direct landfall in the U.S., moisture associated with the system interacted with an upper level trough across the Southeast bringing record rainfall and flooding to parts of the Carolinas.

The Accumulated Cyclone Energy (ACE) index of tropical cyclone activity also indicated a below-average season in the North Atlantic. The ACE index is used to calculate the intensity of the hurricane season and is a function of the wind speed and duration of each tropical cyclone. The 2015 Atlantic hurricane season had an approximate ACE of about 60 (x104 knots2) which was below the 1981-2010 average value of 104 (x104 knots2) and slightly less than the ACE value of 2014. Almost half of the ACE during the 2015 was attributable to a single hurricane, Joaquin, which was the strongest hurricane of the season with maximum sustained winds of 155 mph (Category 4 strength) and a central minimum pressure of 931 mb.


East Pacific Basin

2015 Season Summary:

The 2015 East Pacific hurricane season had 18 named storms, including 13 hurricanes, nine of which became major. The 1981-2010 average number of named storms in the East Pacific is 16.5, with 8.9 hurricanes, and 4.3 major hurricanes. This is the first year since reliable record keeping began in 1971 that the eastern Pacific saw nine major hurricanes. The Central Pacific also saw an above-average tropical cyclone season, with 14 named storms, eight hurricanes, and five major hurricanes, the most active season since reliable record-keeping began in 1971. Three major hurricanes (Ignacio, Kilo and Jimena) were active across the two adjacent basins at the same time, the first time this occurrence has been observed. The ACE index for the East Pacific basin during 2015 was 158 (x104 knots2), which is above the 1981-2010 average of 132 (x104 knots2) and the highest since 2006. The Central Pacific basin ACE during 2015 was 124 (x104 knots2).

Two major hurricane records were broken in the East Pacific basin during 2015. Hurricane Patricia was the strongest hurricane on record in the Western Hemisphere with maximum sustained winds of 200 mph and a central pressure of 879mb. Hurricane Sandra, which formed at the very end of the season in November had maximum sustained winds of 145 mph and was the strongest hurricane in the East Pacific so late in the year. The remnants of several East Pacific tropical cyclones made their way into the contiguous U.S. during the year, bringing flooding rains to parts of Southern California, the Southwest, and the Southern Plains.

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Tornadoes

Similar to the past three years, tornado activity across the U.S. during 2015 was below average. During January-September, there were 948 confirmed tornado reports, with 238 reports still pending for October-December. This brings the 2015 preliminary tornado count to 1,183 with the final count expected to be lower. The 1991-2010 annual average number of tornadoes for the U.S. is 1,253. The 2015 tornado count will exceed 1,000, which is the first time since the hyper-active year of 2011, and is more than the 888 tornadoes that occurred 2014. As with most years, there were several large and destructive tornado and severe weather outbreaks during 2015. There were 34 tornado-related fatalities, 10 of which occurred in May and 24 in December. The deadliest tornado outbreaks of the year occurred in late December, with strong tornadoes striking across the South, including across the Dallas, Texas metro area. There were at least five severe weather outbreaks that caused damages exceeding one billion U.S. dollars.

The number of tornado-related fatalities during 2015 was remarkably low prior to the late-December outbreak. There were 34 total fatalities, but before the December outbreak was on track to beat the 15 deaths that were reported in 1986 to become the lowest annual tornado-related fatality count in the 1950-present period of record. The deadliest single tornado of the year occurred in northern Mississippi on December 23rd with the EF-4 resulting in nine fatalities. An EF-4 three days later that hit near Dallas, Texas resulted in eight fatalities. Additional information on the deadly December in the South is available in our December tornado report. The deadliest tornado year for the U.S. occurred in 2011 when there were 553 tornado-related fatalities.

Most months had near- to below-average tornadoes, with the exception of May, November, and December. In May, there were 414 confirmed tornadoes, well above the 1991-2010 average of 276 for the month. This marked the fourth most active May in terms of the number of tornadoes, with more observed during May of 2008, 2004, and 2003. This was also the most active tornado month for the U.S. since April 2011 when over 750 tornadoes were confirmed. There were seven tornado-related fatalities during May, the highest monthly count during 2015. The following month, June, only had 184 confirmed tornadoes, which was much less than the 1991-2010 average of 243. During November, there were 95 preliminary tornado reports which is more than the average of 58 and the most since 2005. Most of the tornadoes occurred in two separate outbreaks. In mid-November an outbreak spawned an estimated 47 tornadoes across the western Great Plains, which was unusual for that late in the year in the region. In December, there were 86 preliminary reports which is well above the average of 24.

For additional information on specific tornado and severe weather events during 2015, please visit our monthly reports, the Billion Dollar weather disasters report, the Storm Events Database, and NOAA's Storm Prediction Center.

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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.


Citing This Report

NOAA National Centers for Environmental Information, State of the Climate: National Overview for Annual 2015, published online January 2016, retrieved on May 6, 2016 from http://www.ncdc.noaa.gov/sotc/national/201513.