May 10, 2011

April Saw Wild Climate Extremes In The United States

April 2011 was an extreme climate month of historic flooding, a record-breaking tornado outbreak and devastating wildfire activities in much of the United States, scientists at NOAA's National Climatic Data Center (NCDD) say.

The monthly analysis provided by NOAA, based on records that date back to 1895, showed that the average U.S. temperature in April was 52.9 degrees F, which is 0.9 degrees F above the long-term average (1901-200); and the precipitation was 0.7 inches above the long-term average, resulting in the 10th wettest April on record.

Six states "“ Illinois, Indiana, Ohio, Kentucky, Pennsylvania and West Virginia "“ had the wettest April since 1895, with Kentucky getting nearly a foot of rain, which is more than three times its norm for the month, NOAA reports.

Even with all the rain, the U.S. had the most acres burned by wildfire since 2000; and Texas is in a severe drought category that is aggravated by the 5th driest April on record for Texans.

In addition, a record of 305 tornadoes hit the U.S. from April 25-April 28, killing at least 309 people, with death toll and total tornado damage figures still being finalized, reports the Associated Press (AP).

The United States saw the southern and eastern states with near record heat for April, while the northwestern states experienced cooler than normal temperatures. The month, however, was warmer than normal, but not record-setting.

La Nina and the cooling of the central Pacific Ocean, which causes storm tracks to lock in along certain paths, are to blame for this odd mix of extreme weather of showers and drought, says Mike Halpert, deputy director of NOAA's Climate Prediction Center.

"It's very consistent with La Nina; maybe we've had more extremes," Halpert told AP. "It's a shift of the jet stream, providing all that moisture and shifting it away from the south, so you've seen a lot of drought in Texas."

However, U.S. scientists have yet to find evidence that point a finger at La Nina as the culprit for last month's deadly tornadoes.

Air instability, wind shear and water vapor are three major factors that create tornadoes. Martin Hoerling, research meteorologist at NOAA did not find any long-term trends that point to either climate change or La Nina when he tracked these three factors.

According to climate models, the changes in instability and water vapor will increase the chances of severe thunderstorms and maybe even tornadoes in the future. However, NOAA research meteorologist and tornado expert Harold Brooks says that it may take another 30 years for the predicted slow increase to be statistically noticeable.

Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research in Boulder, Colorado disagrees and says that the preliminary study conducted by Hoerling is flawed and too simplified, reports the AP. Instead, he says that evidence exists that the increased instability in the atmosphere is happening right now.


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