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National Overview

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In 2010, the contiguous United States (CONUS) average annual temperature of 53.8 degrees F (12.1 degrees C) was 1.0 degrees F (0.6 degrees C) above normal, and was the 23^rd warmest year on record. Since 1895, the CONUS has observed a long-term temperature increase of about 0.12 degrees F (0.07 degrees C) per decade. Precipitation across the CONUS in 2010 was 1.02 inches (25.9 mm) above the long-term average (LTA). Over the long-term, precipitation averaged across the CONUS, is increasing at a rate of about 0.18 inches (4.6 mm) per decade.

Seasonal highlights in 2010 included a winter with abnormally cold temperatures and abundant moisture, which resulted in a historic December-February period in the East and Northeast. Several locations broke monthly and seasonal snowfall records. During the spring period, record warmth dominated much of the Northeast contributing to the limited amount of snow fall across the country. Satellite measurements indicated that the U.S. had its 8^th smallest April snow cover extent in the 44-year period of record. The North Atlantic High played a large role in the summer weather pattern along the east coast, contributing to record heat in the South and East. A persistent storm track brought prolific summer rains to the Northern Plains and Upper Midwest. The number of tornadoes, as reported by the Storm Prediction Center (SPC), during the summer was abnormally high—sixth busiest in 60 years. Drought conditions, while record low at the beginning of the summer period, expanded in area by late summer. Nonetheless, the U.S. footprint of drought reached its smallest extent which help limit wildfire activity in 2010. For the second consecutive year, no hurricanes made landfall in the U.S., despite the active tropical cyclone season in the Atlantic Basin.

This annual report places the temperature and precipitation averages into historical perspective, while summarizing the notable events that occurred in 2010. More detailed analysis on individual months can be found through the Climate Monitoring home page.

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Top Ten U.S. Weather/Climate Events for 2012

The following is a list for the top ten U.S. weather/climate events which occurred during 2010. These events were selected by a panel of weather/climate experts from around the country. For additional information on these events, please see our Top Ten U.S. Events webpage.

Rank	Event
1	Consecutive Winter Blizzards/ Extreme Snow Season
2	Nashville and Central TN flooding
3-tie	Hot Summer in the East
3-tie	Midwest Super Storm
5	Hawaiian Drought
6	No hurricanes made U.S. landfall despite active Atlantic
7	Near Eradication of CONUS Drought
8	Vivian, SD Hailstone
9	New England Flooding
10	Minnesota as tornado leader

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Temperature and Precipitation Seasonal Analysis

Winter

The 2009/2010 winter season was marked by anomalously cold air in the South and East. Temperatures for the three-month period (December–February) were dominated by the historically strong negative phase of the Arctic Oscillation (AO). The negative AO allowed cold Arctic air to slide south while warmer air was displaced to the north. This created warmer-than-normal conditions in some of the Northeast, Great Lakes and Northwest, while below to much-below-average temperatures were present from the Rockies eastward into the Mid-Atlantic. The coldest temperature anomalies for the period occurred in the Southeast and Southern Plains. Florida was greatly affected by the persistence of the cold air. In January, its citrus crop sustained heavy damages from sub-freezing temperatures as an estimate by the U.S. Department of Agriculture totaled the crop losses to be more than $450 million. Florida then experienced its fourth coldest February on record. Temperature anamolies were nearly eight degrees F (4.4 degrees C) below the 20^th average. Meanwhile, Maine had its third warmest winter, nearly six degrees F (3.3 degrees C) above the 20^th century average. The average winter temperature across the contiguous U.S. was 1.8 degrees F (1.0 degrees C) below the 20^th century average, or 15^th coolest on record.

The strong presence of El Niño coupled with the negative AO, greatly influenced the jet streams and general weather pattern across the U.S. during the winter period. The average precipitaton for the period was 0.88 inch (22 mm) above normal partly due to a series of winter storms that were generated by the subtropical and polar jets. As a result of the persistent pattern, much of the South, East, and Upper Midwest experienced above to much-above-normal precipitation. One of the note-worthy events during the season were the back-to-back winter storms that affected the Washington D.C. area in February. The first occurred on February 4^th when the Reagan National Airport received 32.4 inches (82.3 cm) of snow, a record amount for that location. On February 9^th-11^th, while digging out from the previous storm, D.C. residents suffered through another storm as 10.5 inches (26.7 cm) of snow fell at the Reagan National Airport. While there were no record precipitation amounts statewide, monthly and seasonal snowfall records were shattered.

Spring

The nationally averaged temperature for the spring period (March-May) was 1.4 degrees F (0.8 degrees C) above the LTA. The season brought record warmth to the Northeast, which was 5.3 degrees F (2.9 degrees C) above normal. Eight northeastern states experienced their warmest such period on record: Connecticut, Rhode Island, Maine, Massachusetts, New Hampshire, New Jersey, New York, and Vermont. Michigan also had its warmest spring period. It was one of the ten warmest spring seasons for ten other states. Conversely, the majority of the western U.S. experienced temperatures that were 2-4 degrees F (1.1-2.2 degrees C) below normal during the spring season. A persistent pattern of a high pressure ridge (associated with warmer conditions) in the East and a western trough (cooler conditions) was especially evident during the period. Much of the coolness in western U.S. can be attributed to unrelenting troughs which filtered in cool moist Pacific air during April and May.

As is typical, precipitation was variable throughout the country during the spring season (March–May) resulting in a near-normal value based on the LTA. Only three states were in the top or bottom tenth percentile. Louisiana had its fifth driest period while Rhode Island and Massachusetts had their second and tenth wettest period, respectively. During the period, warm conditions across the Northeastern quadrant of the country helped limit U.S. snowfall. Several cities in New York did not receive any snow during the month of March for the first time on record. Satellite measurements indicated that the U.S. had its 8th smallest April snow cover extent in the 44-year period of record, while North America as a whole had its smallest spring snow cover extent. As estimated by the U.S. Drought Monitor (USDM), the area of drought in the CONUS increased slightly from 8.8 percent at the beginning of March to 9.3 percent near the end of May. Flooding occurred in Nashville, Tennessee when a stagnant storm system brought more than 13.0 inches (330.0 mm) of rain to the area on May 1^st-2^nd. It was estimated that over $1 billion worth of damages were done. By the second day of the month, Nashville had recorded its wettest May and fifth wettest month on record.

Summer

The summer of 2010 was marked by the persistent Bermuda High that parked itself in the western Atlantic. This area of high pressure was situated abnormally west ushering in warm humid conditions along the east coast and as far inland as the Midwest. This not only lead to record heat in a vast area of the country, but also acted as a block preventing smaller storm systems from entering into the regions. It was the hottest June on record for several states along the mid-Atlantic Coast as well as Louisiana. Nationally, it was the eighth warmest June and August on record. During the first week of July, an oppressive heat wave led to soaring temperatures throughout the eastern half of the CONUS. Hundreds of maximum high and minimum high temperatures were broken, contributing to the third and the fifth warmest July on record for the Southeast and Northeast climate regions, respectively. For the entire summer period (June-August), 12 states were record warm, while only two experienced average temperatures below normal. Overall, it was the fourth warmest summer on record for the CONUS with an average temperature of 1.9 degrees F (1.0 degrees C) above the 20^th century average.

Despite record warm temperatures during the summer period, the nationally averaged precipitation was the ninth wettest in 116 years, 1.09 inches (27.7 mm) above the LTA. As a result of the persistent track of storm systems across the northern-tier states, areas around the Upper Midwest and Great Lakes had an anomalously wet summer. Wisconsin had its wettest June–August on record, while many other surrounding states, including Iowa, Michigan, Nebraska, South Dakota, Minnesota, and Illinois, had near record precipitation averages. New Jersey was the only state to experience a summer that ranked in the bottom ten percent (6^th driest), based on data that date back to 1895. Regionally, both the West and Southeast had below-normal precipitation averages during the summer season.

Fall

Warmer-than-normal temperatures were predominant throughout much of the country during the fall season (September–November). Based on divisional temperature averages, no state experienced a below-normal fall period. These conditions were mostly reflective of the above-average warmth during September and October, a result of the lingering Bermuda high in the Atlantic. The average fall temperature for the CONUS was 1.5 degrees F (0.8 degrees C) above the 20^th century average, ranking 14^th warmest. The constant lack of precipitation in Florida resulted in the second driest September-November period on record. Meanwhile, the tireless storm track over the upper Midwest resulted in much-above-normal precipitation for Minnesota and North Dakota. Maine, Vermont, and New Hampshire also averaged precipitation amounts that were among their wettest ten percent. Overall, precipitation when averaged nationally, was about average for the fall period.

Fall highlights consisted of:

• On September 27^th Los Angeles, California experienced its all-time warmest day (113 degrees F or 45 degrees C) since record keeping began in 1877.
• Major flooding occurred along the Atlantic coast attributable to the remnants of Tropical Storm Nicole
• Severe weather caused eight tornadoes in a single day in Arizona, which only averages four per year
• A powerful low pressure system developed in the Upper Midwest and broke state records for lowest atmospheric pressure observed in Wisconsin
• Winter weather impacted areas in the Upper Midwest as Duluth, Minnesota had its sixth snowiest autumn on record.

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Alaska Annual Summary

Alaska temperatures in 2010 were above the 1971-2000 average, continuing the upward trend of the last 20 years. Winter temperatures in 2009-2010 were 3.1 degrees F (1.7 degrees C) above average. Spring temperatures were 0.7 degrees F (0.4 degrees C) above average, summer was 0.4 degrees F (0.2 degrees C) above average, and fall was 3.1 degrees F (1.7 degrees C) warmer than the average.

Precipitation in Alaska in 2010 was near normal. While it was the fifth driest winter, spring was near normal. Summer precipitation was about 11 percent above the 1971-2000 average and fall precipitation was near normal.

In November, a widespread rain-event coupled with sub-freezing surface temperatures in Alaska resulted in a major ice storm. It was reported that the affected area was the combined sizes of Texas, Oklahoma, and New Mexico. The rainfall amount was the second largest daily rainfall amount between November and March in Fairbanks since record keeping began in 1904.

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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 (> 90^th percentile) of their historical distribution are considered "very warm/very wet" and those in the bottom ten percent (< 10^th percentile) are "very cold/very dry".

During 2010, the U.S. experienced an extremely cold winter which transitioned into a record breaking warm summer. In terms of the area of the contiguous U.S., 38 percent experienced temperatures that were in the bottom 10^th percentile or categorized as "very cold" in December. This definition correlates well with "much below normal" in terms of NCDC ranking methods. The anomalously cold temperatures infiltrated into the U.S again in February when 27.4 percent of the country was categorized as "very cold". Influenced by a weakening El Niño and a strengthening Bermuda High, "very warm" conditions prevailed in the spring and culminated in the summer months. During April, June, and August at least 30 percent of the country experienced conditions that are categorized as "very warm".

Conditions that are categorized as "very wet" existed throughout the U.S. during January–December, resulting in a historically low drought footprint on July 6^th. While the high pressure systems, which typically deliver very little precipitation, dominated the east, the persistant upper level jet stream over the northern tier states produced copious amounts of precipitation for the Upper Midwest. During six of the first seven months of the year (each month except March) conditions categorized as "very wet" prevailed over conditions categorized as "very dry". Furthermore, conditions categorized as "very dry" only existed for greater than 10 percent of the country during three months—March, September and December.

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Lower Tropospheric

The 2010 temperature in the lower troposphere was slightly above-average. Data collected by NOAA's TIROS-N polar-orbiting satellites and adjusted for time-dependent biases by NASA and the Global Hydrology and Climate Center at the University of Alabama in Huntsville, indicate that temperatures in the lower half of the troposphere (lowest 8 km of the atmosphere) over the U.S. were approximately 0.2 degrees F (0.1 degrees C) above the 1979-1998 average.

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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. During 2010, the most prominent and wide-spread extremes occurred during two seasons: winter and summer. At the National level, the winter season ranked as the 15th coldest winter on record, while the summer ranked as the 4th warmest based on records which date back to 1895. The change in seasonal temperatures was a record in the Southeast, which experienced its 11th coldest winter and its hottest summer on record. Winter precipitation was above average across the nation with the Southwest and the Southeast ranking among the top ten wettest such periods on record. Summer ranked 9th wettest for the nation, with the bulk of the precipitation occurring in the West North Central and East North Central regions.

For the contiguous U.S. (CONUS), the spatial extent of extremes, as depicted by the CEI, was approximately 6% greater than the historical average for winter (December 2009 - February 2010). Factors contributing to the elevated 2009-2010 winter value were large footprints of cold maximum temperatures, areas of extreme wetness as denoted by the Palmer Drought Severity Index (PDSI) and an abundance of days in which precipitation fell. The seasonal wetness can also be seen in the precipitation state rank map. Regions of the country which were most significantly impacted were the Central, South and Southeast regions. More than half of the Southeast region experienced extremes in cold maximum temperatures, excessive wet conditions and large 1-day precipitation events. Approximately one-third of both the Central and South regions experienced extremes in cold maximum temperatures, excessive wetness and a large number of days with precipitation. Other regions which had prologed periods of wetness were the West North Central, East North Central and the Northeast regions.

For as cold as the winter was in the Central, South and Southeastern regions, the summer months were filled with record warmth, primarily seen in the warm minimum temperatures. Approximately 30% of the CONUS was impacted by extremes during the summer (June August), which is 10% above the average spatial extent for extremes. Much of the credit for this above average value can be attributed to warmth in both maximum and minimum temperatures as well as excessive wetness across parts of the contiguous U.S. More than half of the East North Central region experienced extremes in warm minimum temperatures, excessive wetness, large 1-day precipitation values and a large number of days with precipitation. The Southeast region sweltered under large-scale heat in both maximum and minimum temperatures, which covered nearly the entire region during the summer months. Nearly all of the Northeast, Central, Southeast, South and East North Central regions experienced extreme warm minimum temperatures during this period. The Southwest and West North Central regions had large, yet less-extensive areas which experienced warm minimum temperatures during this period. Additional areas of extreme wetness were also seen in the West North Central, Northwest and Central regions.

In 2011, the regional CEI data and graphics will be updated on a monthly basis and accessible through the CEI webpage. Please visit our main CEI webpage for national CEI data as well as updates on the timing of the release of the regional CEI products.

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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.