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State of the Climate
National Overview
January 2011

National Oceanic and Atmospheric Administration

National Climatic Data Center


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National Overview Report
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National Overview Report

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Temperature and Precipitation Ranks
U.S. Percentage Areas
More Information

National Overview:

The weather pattern over the contiguous United States during January 2011 consisted of a broadscale high pressure ridge over the West and a low pressure trough over the East. Temperatures averaged above normal in the Pacific Coast states under the upper ridge, while cooler-than-normal temperatures dominated east of the Rockies under the upper trough.

Strong storm systems moving in this flow pattern brought rain and snow to many areas. Pacific extra-tropical cyclonic systems moved across the Northwest and northern Rockies then intensified as they moved into the Great Plains states. Nebraska and North Dakota each had the 12th wettest January on record. Other winter storm systems developed over the Southern Plains, tapping Gulf of Mexico moisture as they moved across the southern states and intensified and finally tracking up the Atlantic Seaboard. Several of the low pressure sytems and associated cold fronts brought severe weather to the Gulf Coast, including several tornadoes to central Florida. The northern systems and Gulf systems exited the country in the Northeast.

The combination of Gulf moisture and cold Canadian air resulted in widespread snowfall. January began with about 50 percent of the contiguous U.S. under snow cover and ended with about 42 percent snow covered, but the snow cover area varied with each snowstorm during the month, reaching a maximum of about 71 percent of the country on January 12th. Based on the 45-year satellite record, January 2011 had the 5th largest January snow cover extent for the country. Snow has a lower moisture content than rain, so it takes more snow (on average, about ten times as much) to equal the same amount of precipitation (meltwater equivalent) that would fall as rain. These winter storm systems brought above-normal snowfall but below-normal rain to many areas, giving the impression of wet conditions when, in fact, total precipitation was below normal. The southwestern U.S. was unusually dry beneath the upper ridge, with New Mexico having the driest January in the 117-year record and Arizona and Nevada ranking 2nd driest. Many states along the Mississippi River and eastward were drier than normal, with Virginia ranking 5th driest and North Carolina 9th driest. For the nation as a whole, January 2011 ranked as the 9th driest January in the 117-year record.

Cold fronts and low pressure systems moving in the storm track flow are influenced by the broadscale atmospheric circulation. Two such large-scale atmospheric circulation patterns were dominant during January. The first was the La Niña, which is the phenomenon created by cooler-than-average sea surface temperatures in the eastern tropical Pacific Ocean. La Niña is typically associated with wet conditions in the northwest states and Ohio Valley this time of year, cooler-than-normal conditions in the Far West and North Central states, and warm and dry conditions in the southern tier states and Atlantic Seaboard. The second atmospheric circulation index was the Pacific/North American (PNA) pattern, which was positive during much of January. A positive PNA is typically associated with colder-than-normal temperatures over the southeastern half of the country and warmer-than-normal temperatures along the Pacific Coast at this time of year (December-February). The typical precipitation pattern associated with a positive PNA is drier than normal along and east of the Mississippi River, parts of the interior West, and in the Pacific Northwest. The temperature pattern for January 2011 matched what is expected for a positive PNA, while the precipitation pattern was a combination of positive PNA in the East and La Niña in the West.


Alaska Temperature and Precipitation:

For additional details about recent temperatures and precipitation across the U.S., see the Regional Highlights section below and visit the Climate Summary page. For information on local temperature and precipitation records during the month, please visit NCDC's Records page. For details and graphics on weather events across the U.S. and the globe please visit NCDC's Global Hazards page.


Regional Highlights:

These regional summaries were provided by the six Regional Climate Centers and reflect conditions in their respective regions. These six regions differ spatially from the nine climatic regions of the National Climatic Data Center.

See NCDC's Monthly Records web-page for weather and climate records for the most recent month. For additional national, regional, and statewide data and graphics from 1895-present, for any period, please visit the Climate at a Glance page.


PLEASE NOTE: All of the temperature and precipitation ranks and values are based on preliminary data. The ranks will change when the final data are processed, but will not be replaced on these pages. Graphics based on final data are provided on the Temperature and Precipitation Maps page and the Climate at a Glance page as they become available.


Citing This Report

NOAA National Climatic Data Center, State of the Climate: National Overview for January 2011, published online February 2011, retrieved on May 25, 2012 from http://www.ncdc.noaa.gov/sotc/national/2011/1.

Questions?

For questions on technical or scientific content of this report, please contact:

Jake Crouch:
Jake.Crouch@noaa.gov

For general climate monitoring questions, please contact:

CMB.Contact@noaa.gov

For climate data orders, please contact the National Climatic Data Center's Climate Services and Monitoring Division:

NCDC.Orders@noaa.gov

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