Friday, January 27, 2012

More Cold

Scott Bachmeier sent a link to this false color infrared image from early Friday morning (I've reoriented the original image to be longitudinally centered over Alaska):

The purple colors are radiance derived temperatures -50C (-58F) and lower. Over mainland Alaska any temperatures this cold are surface temperatures. These are a bit lower than the surface observations. The difference comes from several different sources, the most of significant of which are satellite calibration and the fact that "surface observations", i.e. METARS, cooperative obs, etc are from thermometers exposed above the surface. Nominal exposure 1.5 to 2 meters above the ground, though some are routinely higher (SNOTEL, RWIS). The presence of the mid-winter snowpack makes the actual thermometer exposure something like 0.5 meters lower in most places north of the Alaska Range.
Skies cleared by mid-morning over Fairbanks. By Noon temperatures have been down to 41 below at the Airport and 42 below at Fort Wainwright and Goldstream Valley.

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