Warm & Dry Winter Weather Continues to Prevail in U.S.

Climate data is in for the month of January that has just passed, and the lower-48 of the United States has recorded its 4th warmest January since reliable records began in 1895. Most of the warmth was concentrated in the Midwest and Great Plains states, where a winter largely without significant snowfall to speak of continues almost unabated with little forecast change in sight. As snowpack and eventual snowmelt is a large contributor to soil moisture at the start of the growing season, this spells a building drought threat that could have significant impacts on this year’s harvest. See the images below for a more detailed look:

January 2012 departure from normal for temperatures.

January 2012 departure from normal for temperatures.

Note that with the exception of slivers of California, Oregon, and New Mexico, the state of Washington, and south Florida, the entire country saw January temperatures that were above normal.

January precipitation departure from normal.

January precipitation departure from normal.

When precipitation is considered, most of the country also came in drier than normal, with the exception of a dominant storm track that went from central Texas through the eastern Great Lakes states. This storm track helped Texas record its second above normal precipitation total for a month since February of 2010. Much of that state still remains mired in a multiyear drought however. As far as the entire country goes, January 2012 comes in at the 28th driest January since 1895. Even with the severe winter storms that have lashed the Pacific Northwest this past month, it has only been able to move the needle from “below normal” to just average for precipitation.


The dry and warm January continues to be the result of an otherwise wet weather-filled pattern known as La Niña being completely counteracted by a much harder to predict pattern in the Atlantic called the North Atlantic Oscillation. The NAO has kept winds in the atmosphere moving quickly from west to east across the eastern 2/3 of the North American continent, which in turn prevents large scale intrusions of cold air from the Canadian arctic as well as large moisture-laden storms from forming and tracking across the U.S. This is the same weather pattern that gave much of the country – even the parts that typically see snow for the holidays – a brown Christmas.

More spring-like conditions over the eastern U.S. has allowed more spring-like weather phenomenon to occur. A tornado outbreak across the Deep South on January 22nd helped propel January to the 2nd most reported tornadoes for a January since 1950 at 95. As the pattern has extended into February, other spring anomalies have occurred, the latest being a tropical depression trying to spin up south of the Florida Keys – only four months ahead of schedule.

Beyond this winter, the longer term trend has been for more winters like these than not. The percentage of the country ending up “very warm” in January continues to outpace the percentage of the country being “very cold” – defined by the National Climatic Data Center as follows:

The percentage areas of the contiguous United States are computed based on the climate division data set. Those climate divisions having the monthly average temperature in the top ten percent (> 90th percentile) of their historical distribution are very warm and those in the bottom ten percent (< 10th percentile) are very cold.

With that in mind, note the chart of “Very Cold/Warm” since 1895:

Percentage of the lower-48 U.S. either very warm or very cold in the month of January since 1895.

Percentage of the lower-48 U.S. either very warm or very cold in the month of January since 1895.

Note that even with the supposedly cold and harsh winters that were seen in the previous few years, the five-year average of amount of territory very warm never dropped to zero, and the amount of territory very cold barely moved from a near flat-line trend that has held largely unabated since the early 1990′s. While this year may be an outsider for the time being, the general trend is to continue very warm winters for larger and larger portions of the United States.

For what it’s worth, the numbers for July are even more disconcerting:

Percentage of the lower-48 U.S. either very warm or very cold in the month of July since 1895.

Percentage of the lower-48 U.S. either very warm or very cold in the month of July since 1895.

While winters are on average becoming more mild, summers are just getting plain hot. The five year average for “very warm” has been fairly stable near or above 25% of the country every year since 2002. If that trend continues this year, it will make ten straight years of such conditions – far eclipsing the five years of similar warmth from 1934 – 1938, during The Dust Bowl.

So while this winter continues to feel like an aberration - it is absolutely one when considering the past – it may seem less-so in future winters.

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