Wednesday, January 4, 2012

Deep Cold Air

This morning's upper air sounding is a fairly typical one for a deep cold airmass in Interior Alaska. There is a shallow layer near the surface with temperatures nearly constant, a transition layer where the temperature increases fairly smartly with height, and then the "warmest" air is above that. On this morning's sounding, between 3000 and 10000 feet above the ground, the temperature only varies by a few degrees, and the warmest temperature (+1F) was at nearly 7000' AGL.

This illustrates nicely that super strong inversions are NOT a feature of deep cold; the strongest inversions occur when skies are clear and it is warming aloft.

Low temperatures in the valley this morning were a couple hours either side of midnight, with the Airport bottoming out at 39 below. Clouds have since come in broken the small inversion that formed late last evening. At hill elevations that are still in the coldest layer, temperatures have been close to 30 below since yesterday. The very highest weather stations in Fairbanks-land, those above 2300' MSL, are the only sites reporting temperatures warmer than 10 below this morning. At the Caribou Peak RAWS, at 2500' MSL north of Poker Flats, temperatures in the past 24 hours have held between zero and 9 below.

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