Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 17. joulukuuta 2007 klo 15:23 (GMT)
We've got a real winter on our hands in North America this December. The latest in series of storms that has pounded the continent left nearly a foot of snow over portions of Michigan, New York, Massachusetts, Maine, and Canada Sunday. Heavy snow collapsed the roof of a pharmacy in Boston, injuring one person yesterday. Heavy ice accumulations were a problem in Pennsylvania, where ice and high winds brought down the 800-foot high TV tower of WNEP-TV. A possible tornado associated with the storm's trailing cold front swept through Land 'O Lakes, Florida early Sunday morning, destroying a jail and flipping cars. No one was injured, and the inmates were moved to safety before the storm hit.
Figure 1. Departure of surface temperature from average for the period December 1-15, 2007. Note that the northern U.S. has seen below average temperatures, but the southern U.S. has seen above average temperatures. Temperatures across most of Europe and Asia have been much above average. Temperatures over ocean areas are not reliable in this data set, and should be ignored. Image credit: NOAA ESRL.
This winter's jet stream pattern
When this year's record sea ice melt in the Arctic occurred, I predicted another late arrival to winter over the Northern Hemisphere, because of all the extra heat and moisture the loss of sea ice would provide to the polar atmosphere. Well, winter arrived pretty much on time over North America. We've seen temperatures near average during the first half of December (Figure 1). However, almost all of Europe and Asia have seen a delayed start to winter. First half of December temperatures have been 3-6°C (5-10°F) above average across most of Europe, and even warmer over much of Asia. While the ski areas of the Alps have gotten much more bountiful snow than last winter, the lack of cold temperatures and snow is hurting the tourist industry in many regions, such as Finland. In Eastern Siberia, the lack of usual sea ice has led to temperatures up to 15°C (27°F) above average during the first half of December. The missing sea ice between Russia and Alaska has also brought unusual storminess and low pressure to the region during November and December. This may have deflected the position of the jet stream, bringing colder conditions to North America than the rest of the Northern Hemisphere. The current La Nina event and natural variability are also involved, and it is difficult to say which effect is mostly responsible for the current jet stream pattern.
What does the rest of December hold in store? Well, the latest 16-day forecast from the GFS model shows no major changes to the jet stream pattern. Expect a continuation of normal winter weather over North America, and much warmer than average conditions over Europe and Asia.
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