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Arctic oscillation plays cold winter hand

Friday, January 28, 2011 | 6:43 p.m. CST; updated 9:23 p.m. CST, Friday, January 28, 2011
The Arctic oscillation process involves two phases that help to determine the temperatures of the northern hemisphere.

COLUMBIA — The negative phase of the Arctic oscillation phenomenon has trumped earlier predictions for this winter based on a weak La Niña.

The Climate Prediction Center based its winter prediction in November on the La Niña phenomenon, a cooling of waters in the eastern tropical Pacific.

Anthony Lupo, MU professor of atmospheric science, said mid-Missouri has been under the influence of an Arctic oscillation, a fluctuation of atmospheric temperatures and pressures around the North Pole that influences temperatures in North America and other parts of the middle latitudes.

The Arctic oscillation is in a "negative phase" that translates into warmer temperatures in the Arctic and colder temperatures in the middle latitudes.

"Typically, during the negative phase of an Arctic oscillation, we see the jet stream dive out of Canada and bring with it some cold Arctic air masses," Pat Guinan, a climatologist at MU, said. “It has been ongoing since December, so that is why we have seen these below-normal temperatures for this winter."

Guinan, who works for MU Extension’s commercial agriculture program, said it’s difficult to take the Arctic oscillation into account more than two weeks in advance.

"On the other hand La Niña is a little bit more stable in regard to its persistence and how long it will last," Guinan said. "And there is higher confidence that it will persist throughout the winter, and indeed it has."

Lupo said that predicting the interaction between La Niña and an Arctic oscillation "tends to be a little bit of a crap shoot."

Weaker La Niñas are more difficult to predict, but when La Niñas are strong they cooperate with an Arctic oscillation and contribute to colder temperatures in the Midwest.

“They are cooperating this year,” Lupo said. "We had predicted, back in August and September, that this winter would be colder and snowier. Of course, the Climate Predication Center said warmer than normal — and we didn’t believe them."

The warm-up Columbia experienced Thursday and Friday was due to a break in the polar jet stream, Lupo said. The temporary warm-up, he said, "is just a break in the action. … This nice weather is just a result of the jet stream being much less active now, and that has given the sun the chance to warm up the ground."

Lupo expects colder temperatures to return Sunday and Monday, with the possibility of significant snow early next week.

"We are expecting a snowstorm to come in, and the models are saying a lot of different things. This is the kind of event that could be warm enough that would bring in some rain with it and only ... a little bit of snow."

A major winter storm is also possible — depending on the different solutions being offered by computer models used by forecasters. "One model projection has us at 16 inches," Lupo said Friday. "What will probably happen is something in between."

Melted precipitation, or the actual water content of the snow, for this winter has been below normal. Snowfall, on the other hand, has been above normal.

"Since Dec. 1 there has been 3.02 inches of melted precipitation at the Columbia Regional Airport, which is 0.82 inches below normal, and there has been 22.3 inches of snow, which is 12 inches above normal," Guinan said.

Temperatures were around 3 to 4 degrees lower than normal for both the months of December and January in mid-Missouri, which means it will be difficult for the Climate Prediction Center’s winter forecast to be verified, Guinan said.

"In order to verify a winter forecast where we have an above-normal temperature regime throughout we would have to have a very warm February to balance out the colder months we’ve seen in December and January," he said.


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