Record cold in Alaska
Posted by JAC on 11/20/2009, 6:20 am



A McIDAS image of the NOAA-18 10.8 m IR channel (above) showed a region of very cold surface temperatures (darker blue to violet color enhancement) over the interior of Alaska on 19 November 2009. A closer view with an overlay of the surface air temperatures (below) revealed a number of narrow fingers of very cold air - this represented the drainage of the coldest air into mountain valleys. The coldest temperature from first-order reporting stations around the time of the image was -44 F at Bettles (located near the center of the image). Bettles had reported record low daily minimum temperatures of -45 F on 17 November and -46 F on 18 November - this followed a record 2-day snowfall of 23.7 inches on 11-12 November (the greatest 2-day snowfall on record for Bettles during the month of November). However, note that the IR image suggested the presence of a deck of clouds to the east of the very cold valley signatures - and surface air temperatures were significantly warmer under this cloud deck.







AWIPS images of the AVHRR Cloud Type, Cloud Top Temperature, and Cloud Top Height products (below) indicated that the patch of clouds to the east and southest of Bettles (station identifier PABT) was composed of supercooled water droplets (cyan color enhancement), with cloud top temperatures in the -30 to -38 C range and cloud top heights in the 3-5 km range. Note that the cloud product algorithms showed values of cloud properties over the region surrounding Bettles (even though it was clear there) - the very cold surface temperatures tricked the algorithms into thinking that there were high cirrus clouds over that particular area.







GOES-11 10.7 m IR images (below) gave some indication that this cloud deck was moving slowly northward across the region to the east of Bettles (north is toward the upper right corner of these AWIPS images).





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Record cold in Alaska - JAC, 11/20/2009, 6:20 am
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