Upper Level Low, Slow to Go

12/19/14: Something I find fascinating to watch is the flow at the upper levels of the atmosphere. An even more interesting feature is a closed upper low. (basically a storm at the upper levels 18,000’+). The upper level doesn’t move as fast as the surface but not often you see it stall or take a while to move.. On that note…

On December 10 an Upper Level low caught up to a storm off the coast not only slowing the surface storm down but dragging it inland towards New England. On the 10th this ULL was over NYC, on the 13th it was off the coast of Maine! 4 days from NYC to Maine. Typically when the NAO indicator is negative it indicates blocking upstream and slows things down in the Northeast U.S… but it was positive during this period which is interesting.

Then on December 17th another ULL comes pin wheeling from Great Lakes. This morning it was over Nova Scotia.

On the image below you will see the 12z time frame for the dates I mentioned. The shaded colors are the temps at 850mb. Previously it was just a cold pool of air. Last 3 days the airmass has been colder in the U.S but it’s only normal and nothing too cold for this time of year. More importantly note the ULL slow to move out. (500mb Height)

The snowpack and snow amounts across northern New England have been truly impressive this year already. Caribou with 3rd most snow on record to date. Over 4.5 feet of snow already.

If these Upper Lows can drop a bit further south with the air aloft colder than has been than we should be seeing more snow events; but if we get Lake Cutters like on Christmas Eve lets just say Ski resorts wont even like that.

Weather is always fun to look at because #1 there’s always something to learn. #2. Each situation is unique.

~ Ralph


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