Fourth warmest winter on record for the U.S.

February is gone, and the non-winter of 2011 - 2012 is the history books as the fourth warmest in U.S. history, said NOAA's National Climatic Data Center yesterday. The winter average temperature of 36.8°F was just 0.4°F cooler than the warmest winter on record, the winter of 1999 - 2000. If you lived in the Northern Plains, Midwest, Southeast and Northeast, it seemed like winter never really arrived this year--27 states in this region had top-ten warmest winters. Across the U.S., only New Mexico (41st coolest) and Alaska (35th coolest) had winter temperatures colder than average. According to NOAA's Climate Extremes Index, the percent area of the U.S. experiencing extremes in warm maximum temperatures (top 10% on record) was 49 percent--the 4th highest value since the index began being computed in 1911. Jackson, Kentucky, Mount Pocono, Pennsylvania, and Trenton, New Jersey all had their warmest winter on record.


Figure 1. Contiguous U.S. temperature rankings for the winter of 2011 - 2012 (the months of December - January - February.) The 117-year period of record begins in 1895, and each state is given a ranking based on how cold this winter was, relative to the other 116 years. Thus, a ranking of 116 means it was the 2nd warmest winter on record. Image credit: NOAA's National Climatic Data Center.


Figure 2. Contiguous U.S. temperatures for winter (the months of December - January - February), from 1895 - 2012. The winter of 2011 - 2012 was the 4th warmest winter on record, behind 2000, 1999, and 1992. Winter temperatures have increased by abot 1.7°F per century (red linear trend line.) Image credit: National Climatic Data Center.

Third least snowy winter on record for the contiguous U.S.
Warm and dry conditions during the winter of 2011 - 2012 led to snow cover extent that was the 3rd lowest in the 46-year satellite record, according to data from the Rutgers Global Snow Lab. Snowfall was particularly low across parts of the West, where much of California, Nevada, and Arizona had a snowpack less than half of average. Fortunately, the West had a near-record snowpack the previous winter, so this year's lack on snow will not cause serious water availability problems during the summer. In the Upper Midwest, the lack of a winter snowpack will substantially reduce the chances of spring flooding along the Mississippi and Missouri rivers. NOAA issues their annual spring flood outlook on March 15, and it is likely to show a much lower risk of flooding compared to last year, when 1-in-100 to 1-in-500 year floods hit much of the Missouri and Lower Mississippi rivers. However, the remarkably low snow cover this winter over the Upper Midwest will allow soils to dry out much more quickly than usual, leading to increased chances of summer drought. The latest Drought Monitor map shows moderate to severe drought covering nearly all of Minnesota and Northwest Iowa; these regions are at high risk of suffering damaging drought conditions during the summer growing season.


Figure 3. State-by-state rankings of precipitation for the winter of 2011 - 2012. Four Western states had a top-ten driest winters on record, and Kansas had a top-ten wettest winter. Drought-stricken Texas, which entered the winter expecting drier than average conditions, since it was a La Niña year, lucked out, getting an unusually wet winter. Records go back to 1895. Image credit: NOAA's National Climatic Data Center.

A very mild winter for the Midwest
If you live in the Midwest, you saved a bundle this winter on heating and snow removal costs. In Minneapolis, where the low temperature falls below 0°F an average of 30 days each year, the temperature fell below zero on just two days. These days were January 18 and 19, when the low hit -1°F and -11°F, respectively. Since record keeping began in 1891, only one other winter has had so few below-zero days--the winter of 2001 - 2002. Third place is held by the winter of 1930 - 1931, with six below-zero days. Minneapolis has seen half of its usual snowfall this winter--just 22.1" as of March 7, which is 22.1" below the average of 44.2". The least snowy winter for Minneapolis occurred in the winter of 1930 - 1931, when just 14.2" of snow fell on the city.

Chicago has also seen far less snow than usual--just 19.8" as of March 7, 11.8" below their average. In a normal winter, there are 13 days with sub-zero temperatures in Chicago. The coldest it got in Chicago this winter was a relatively balmy 5°F on January 19. This is just one degree cooler than the warmest winter low temperature ever recorded in the city, which is 6°F. Here is a list of the winters in Chicago that have had no sub-zero temperatures, with the coldest temperature of the winter shown in parentheses:

1930-31 (6°F)
1959-60 (6°F)
1905-06 (6°F)
2011-12 (5°F)
1982-83 (3°F)
1938-39 (2°F)
1955-56 (2°F)
1931-32 (1°F)
1881-82 (1°F)
1936-37 (1°F)

NCDC's Dr. Deke Arndt has a two-minute video discussing the reasons for this year's warm winter. The primary factor was the position of the jet stream, which lay much farther north than usual.

I'll be back Monday at the latest with a new post.

Jeff Masters