The first month of Winter in southern Wisconsin

January 2nd, 2010 |
MODIS true color images (01 December 2009 to 02 January 2010

MODIS true color images (01 December 2009 to 02 January 2010

A sequence of MODIS true color images from the SSEC MODIS Direct Broadcast site (above; also available as a QuickTime animation) showed a few snapshots from the first month of Winter 2009/2010 across southern Wisconsin. You can see the transition from bare ground on 01 December…to a few narrow swaths of snow cover early in the month…to widespread deep snow cover on 10 December in the wake of a major winter storm…and finally to all the lakes freezing in the Madison area (located at the center of the images) on 02 January.

December 2009 was the 5th snowiest December on record in Madison, with 26.8 inches falling (the snowiest December was 40.4 inches, recorded in December 2008). The maximum snow depth on the ground at Madison’s Dane County Regional Airport was 13 inches on 09 December; however, a snow depth of 20 inches was reported on that day at McFarland in southern Dane county.

-40º temperatures in Minnesota

January 2nd, 2010 |
MODIS 11.0 µm IR and GOES-12 10.7 µm IR images

MODIS 11.0 µm IR and GOES-12 10.7 µm IR images

AWIPS images of the 1-km resolution MODIS 11.0 µm IR and the 4-km resolution GOES-12 10.7 µm IR channel data (above) showed that large portions of northwestern Minnesota and eastern North Dakota exhibited surface IR brightness temperatures colder than -40º F (-40º C) at 08:45 UTC (2:45 am local time) on 02 January 2010. In northwestern Minnesota, the coldest IR brightness temperature values on the MODIS image were -45º C, compared to -42º C on the GOES-12 image. Note the significantly warmer signature of the Minneapolis/St. Paul urban area, as well as the unfrozen waters of Lake Superior.

A map of the 24-hour minimum temperatures (below; courtesy of MesoWest) showed that 3 sites (Pokegama Lake Dam, Gatzke, and Debs) reported a low of -40º across northern Minnesota on the morning of 02 January.

24-hour minimum temperatures across northern Minnesota (courtesy of MesoWest)

24-hour minimum temperatures across northern Minnesota (courtesy of MesoWest)

Terrain-induced clouds over the Brooks Range in Alaska

January 2nd, 2010 |
POES AVHRR 10.8 µm IR images + surface temperatures (F)

POES AVHRR 10.8 µm IR images + surface temperatures (F)

McIDAS images of POES AVHRR 10.8 µm IR channel data (above) showed the development of a large terrain-induced “banner cloud” over the eastern part of the Brooks Range in northeastern Alaska on 01 January – 02 January 2010. The IR cloud top brightness temperature values were as cold as -65º C (darker red color enhancement) around 20:26 UTC, which suggested very high cloud tops (GOES-11 10.7 µm IR cloud top brightness temperatures were as cold as -58º C at that time). The terrain of the Brooks Range was acting as an obstacle to the northerly flow aloft (ECMWF 700 hPa winds | 500 hPa winds), which helped to initiate the formation of the banner cloud.

This cloud feature was also apparently thick enough to have a dramatic influence on surface temperatures — note that the temperature at Arctic Village (station identifier PARC) rose from -35º F before the cloud feature developed to +1º F after the cloud feature had been overhead for several hours. A surface meteorogram plot indicated that this temperature rise occurred during a period of light winds, so warm air advection could not account for the warming; instead, the thick cloud deck acted as a blanket to stop radiational cooling over that particular site.

CIMSS has been evaluating and testing a variety of CLAVR-x AVHRR cloud products in AWIPS, which can be used to further characterize this banner cloud that formed over the Brooks Range. The Cloud Type product (below) classified the feature as a combination of Cirrus, Multi-level Cirrus, and Opaque Ice Cloud categories (yellow, orange, and red color enhancements), which is not surprising given the very cold appearance on IR imagery.

AVHRR Cloud Type product

AVHRR Cloud Type product

The AVHRR Cloud Top Temperature (CTT) product (below) showed that the tops of the cirrus feature were even colder than what was indicated by the IR imagery, with CTT values as low as -76º C at 20:20 UTC.

AVHRR Cloud Top Temperature product

AVHRR Cloud Top Temperature product

The AVHRR Cloud Top Height product (below) showed that the tops of the banner cloud feature were generally around 8 km (cyan color enhancement). This height was close to the altitude of the tropopause, as indicated on the Barrow AK rawinsonde data.

AVHRR Cloud Top Height product

AVHRR Cloud Top Height product

As an aside, the eastern Arctic Slope region of Alaska was experiencing blizzard conditions during this period — at Barter Island (station identifier PABA) along the coast, winds gusted as high as 72 mph. The strong westerly winds were in response to a tightening pressure gradient in advance of an approaching cold front (surface pressure and frontal analysis).