January 27, 2011

Cold Winter Bucks Trends And Predictions

COLUMBIA, MO - It might not seem that way because of all the recent snowfall, but precipitation this winter is turning out to be a relatively low, said a University of Missouri Extension climatologist.

Temperatures in the state have been colder with less precipitation than expected, bucking recent trends and forecasts from the National Weather Service's Climate Prediction Center.

"Here we are in the middle part of January and we're running below normal in southeastern Missouri in terms of precipitation, as well as likely wrapping up the month with below-normal temperatures for the entire state," said Pat Guinan of the MU Extension Commercial Agriculture Program. "In order to verify the CPC winter outlook, we'll need a very warm February to counter what we've experienced in December and January."

CPC predictions haven't lined up with reality for a few reasons.

Guinan said this year the CPC winter outlook relied mostly on both the impact of the La Niņa phenomenon and temperature and precipitation trends from the past two decades. La Niņa-a period of below-normal sea-surface temperatures in the equatorial Pacific-generally means Missouri will see above-average temperatures over southern sections and above-normal precipitation in the southeastern part of the state.

This winter, however, the Arctic Oscillation (AO), a phenomenon of pressure anomalies in the Arctic, has been a driving factor for our weather patterns.

"We're experiencing a negative AO phase, which drives the polar jet stream southward," Guinan said. "Generally, east of the Rocky Mountains we see below-normal temperatures when we have frequent invasions of Arctic air out of central Canada."

That explanation meshes well with temperature trends in the eastern two-thirds of the U.S. this winter.

"For the most part, December was a cold month and will go down in the record books as being 3-4 degrees colder than average," Guinan said.

Yet this winter hasn't been entirely cold in Missouri. Temperatures rose to the 60s during the last two days of December, and 2010 as a whole averaged above-normal temperatures and precipitation, he said. Worldwide, the year tied with 2005 as the hottest on record, according to NASA and National Oceanic and Atmospheric Administration analyses.

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