The coldest temperature in the United States (including Alaska) was -33 F (-36 C) at Alamosa, Colorado on 03 January 2013. AWIPS images of 375-meter resolution (projected onto a 1-km AWIPS grid) Suomi NPP VIIRS 11.45 µm IR data with METAR surface reports (above) showed a few areas in parts of the higher elevations of central Colorado which exhibited IR brightness temperatures as cold as -44 C or -47 F (white color enhancement). In the lower left portion of the image, the warmer signature (red color enhancement) of the Colorado River basin could be seen running southwestward across Utah and into the Grand Canyon region of Arizona.
Alamosa (station identifier KALS) is located in south-central Colorado, and is situated in the eastern portion of the broad high-altitude basin of the San Luis Valley. The Suomi NPP VIIRS 0.7 µm Day/Night Band image (below) showed the brighter white signature of the moonlit snow-covered San Luis Valley at night (08:49 UTC = 1:49 AM local time). Much of the western (high-elevation) half of Colorado had substantial snow cover, and there were a few other sites that recorded minimum temperatures of -30 F or colder.
A comparison of the Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product” and the corresponding GOES-13 Cloud Thickness and IFR Probability products (below) indicated that most of the higher elevations of central Colorado were generally cloud-free, which allowed for strong radiational cooling to reach such cold surface temperatures.