From the “State of the Climate – National Overview – December 2010” report (www.ncdc.noaa.gov/sotc/national/2010/12) of the USA’s National Climatic Data Center, a department of NOAA.
A strong west-to-east flow in the jet stream circulation characterized the weather pattern over the contiguous United States for December 2010. Deep low pressure systems developed in this flow, resulting in intense winter storms across the nation and outbreaks of cold Canadian air, especially east of the Rockies.
About a third of the country was covered in snow at the beginning of the month. The snow cover expanded and contracted throughout the month with the passage of several winter storms, reaching 39 percent coverage by December 6th, about 53 percent by the 19th, and 55 percent by the 27th.
By the end of the month, more than 8 feet of snow covered higher parts of the Sierra Nevada, with moisture content more than twice normal for this time of year.
December 2010 was the 7th snowiest December for the contiguous U.S., based on satellite observations of area covered. The storm systems triggered deadly tornado outbreaks at the end of the month in the Midwest to Lower Mississippi Valley.
- The national temperature, when averaged across the contiguous U.S., was near normal in December, only 0.4 ??F (0.2 ??C) below the long-term average.
- Regionally, temperatures in the Southwest (2nd warmest) and West (10th warmest) climate regions were much above normal. In contrast, much below normal temperatures dominated the Southeast (3rd coldest) and Central (9th coldest) climate regions.
- Both Florida and Georgia experienced their coldest December on record. The average statewide temperature in Florida was more than 9 degrees F (5.0??C) below the 20th century average, as every climate division in the state experienced an average December temperature that was record cold. In addition, several cities including ??? Miami, West Palm, Ft Lauderdale, Daytona, Orlando, Tampa, and Tallahassee ??? had thier coldest December on record.
- Several other states including ??? North Carolina and South Carolina (3rd coldest), West Virginia (4th), Virginia and Alabama (5th), Tennessee (6th), Kentucky (7th), Mississippi (8th), and Ohio (10th) ??? had a temperature that was among their ten coldest based on records that date back to 1895.
- The average temperature for several states in the West during the month of December was much above-normal. New Mexico had its second warmest December, both Colorado and Arizona had their fourth warmest, while it was Utah’s eighth and Nevada’s tenth warmest such December.
- The cooler-than-normal temperatures can be traced back to the three-month period (October-December) in Florida, its 6th coldest such period. Three states had their eighth coldest October-December period: North Carolina, South Carolina, and Georgia. These below normal temperatures contributed to the Southeast climate region’s ninth coldest such period.
- Many of the contiguous states experienced an annual average temperature that was above the 20th century average. Only four states: Alabama, Florida, Georgia and Mississippi, had an average temperature that was below normal for the year. Of those, Florida’s average temperature for the year was seventh coldest in 116 years, 1.3 degrees F (0.7 ??C) below normal.
- Much of the Northeast was well above normal, as New Hampshire and Rhode Island had their warmest year on record. Maine had its second warmest year, while Vermont, Massachusetts, Connecticut, and New Jersey each had their third warmest such period. Collectively, there were 13 states with annual average temperature that was much above the long-term average.
- Several cities in the Northeast had their warmest year on record: Hartford, Connecticut; Boston, Massachusetts; Caribou, Maine; Concord, New Hampshire; Providence, Rhode Island.
- Precipitation in December, when averaged across the contiguous U.S., was normal, only 0.01 inch (0.3 mm) below the 20th century average. Record precipitation amounts in the west were offset by the dryness in the southern Plains and Southeast.
- The persistent on-shore flow from the Pacific contributed to the third wettest December for the West climate region. These dissipated by the time they reached the South and East, contributing to the second driest December in the South climate region.
- Both Nevada and Utah had their wettest December on record. Other states that were much wetter-than-normal were Minnesota (4th wettest), Maine (5th wettest), North Dakota (6th wettest), California (7th wettest), South Dakota (8th wettest) and Oregon (10th wettest).
- In the South and East several states were drier-than-normal as both Mississippi and Louisiana experienced their third driest December on record. Elsewhere, Kansas had its sixth driest December, Alabama its seventh, Arkansas its eighth, and Delaware its tenth.
- Precipitation in the last quarter (October-December) was extreme for two states. Precipitation in Florida was 5.15 inches below normal resulting in its driest such period. The record dryness in Florida can be traced all the way back to the six-month period (July-December). Conversely, Nevada had its wettest October-December period on record with a statewide average of 3.44 inches (87.4 mm) above the normal. The persistent wetness in the East North Central (2nd wettest) and West (3rd wettest) climate regions can also be seen in the July-December period.
- For the calendar year, precipitation was above normal for most climate regions, except for the South, Southeast and Central. The East North Central climate region had its third wettest annual period on record while its neighbor, the West North Central climate region, had its fifth wettest such period.
- On the statewide level, precipitation averages are reflective of the active storm track across the upper tier states where North Dakota had its wettest calendar year on record. Iowa, Minnesota, and Wisconsin each had their second wettest year on record. It was also anomalously wet in South Dakota, which had it seventh wettest such period. Meanwhile, Louisiana experienced its fifth driest annual period and it was the ninth driest such period for Arkansas.
Other Items of Note
- Tornado activity during December was above average with 59 preliminary reports. The December 31st outbreak across the Mississippi River Valley, with 49 preliminary tornado reports, was largest tornado outbreak during December on record. The previous record was 34 tornadoes on December 18, 2002.
- Several large winter storms affected the U.S. during the month. According to data from the Rutgers Global Snow Lab, the December snow cover extent was the seventh largest on record for the continuous US. Several cities across the Midwest and Northeast broke monthly snowfall records including Minneapolis, Minnesota and Syracuse, New York.
- Drought coverage continued to increased during December. The U.S. Drought Monitor reported 19.9 percent of the United States was affected by drought by December 28th. The wet conditions improved the drought conditions across Utah, Nevada, and California, while conditions worsened across southern Arizona and New Mexico. The drier than average weather across the Southern Plains worsened the drought in most of Texas and Oklahoma by one to three categories. Drought conditions also worsened for the Lower Mississippi River Valley, the Gulf Coast, and most of the Florida peninsula. Several weather systems moving through the Ohio River Valley improved drought conditions there one to two categories and ended drought in the central Appalachians.
For much more detail, visit the source web pages at: “State of the Climate – National Overview – December 2010” report (www.ncdc.noaa.gov/sotc/national/2010/12)