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A look at weather extremes and the big-picture climate connections.

Texas on Pace for Warmest, Driest Year on Record

With the end of the year less than a week away, some noteworthy climate statistics are trickling in to the Climate Central newsroom. First up, the worst one-year drought in the history of Texas may help the Lone Star State set a milestone for the warmest and driest year on record there. Through the end of November, the state was on track to set both those marks, so we'll see if recent rain and snow have put these records just out of reach when the final numbers are calculated.

Precipitation departures from normal during 2011 (through December 27). Credit: NOAA

Climate change projections show that droughts may become more frequent and intense in the Southwest U.S., although this year's drought is thought to have been triggered mainly by La Nina. Some scientists, including the Texas state climatologist, have said the record warmth is likely partly due to global warming.

While Texas and other parts of the Southwest and Southern Plains were parched this year, other areas of the country suffered from a surplus of water. In fact, this year the U.S. saw an unprecedented area affected by extreme drought and unusually wet extremes. For example, in Vermont, Montpelier and Saint Johnsbury have broken their yearly precipitation records, and Burlington only needs 0.15 more inches of precipitation to set a record. 

Thanks to a combination of La Niña in the tropical Pacific Ocean and the positive phase of the Arctic Oscillation, the big cities in the Northeast have had a remarkably snowless and mild start to the 2011/12 winter. No snow fell this month (so far) in New York City and Bridgeport, CT, for example. In Boston, MA, only a trace of snow has been recorded this month, which — if it holds true through the end of the month — would tie for the least snowiest December on record. Hartford, CT, and Worcester, MA, are also on track to tie records for the least snowiest December.

The maps show temperature patterns in late fall/early winter of 2010 (left) and 2011 (right). Places that were warmer than the 1981-2000 average are red, while places that were cooler than average are dark blue.

This is a dramatic reversal from last year, when the Northeast was slammed by heavy snow in December. In Boston, 27.9 inches of snow fell during December 2010, and 20 inches were recorded at New York's Central Park. Also in contrast to the past two winters, December 2011 has been unusually mild in the East.

These trends are clearly linked to the Arctic Oscillation, which is a large-scale variation in surface air pressure between the Arctic and the mid-latitudes. When the Arctic Oscillation is in a strongly positive mode, which it has been so far this month, air pressures are lower than average in the Arctic and higher than average in the mid-latitudes. This setup favors milder than average conditions in the eastern U.S. and Western Europe, as storms tend to take a more northerly track. During last winter and the winter before that, the Arctic Oscillation was in an extremely negative phase, which helped draw frigid air southward and spawn winter storms along the East Coast.

While global warming is not a likely suspect in causing the mild and snowless start to winter, scientists are investigating how climate change-related sea ice loss in the Arctic may be changing atmospheric circulation patterns, such as the Arctic Oscillation.

 

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