CIMSS Satellite Blog

AWIPS images of the GOES-12 6.5 µm “water vapor” channel (above) showed the development of late-season winter storm that produced heavy snowfall and blizzard conditions (with wind gusts to 64 mph or 29 m s-1 at Rapid City SD) across the Black Hills region and surrounding portions of eastern Wyoming, southeastern Montana, and western South Dakota during the 30 April through 02 May 2008 period. A closer view using GOES-12 10.7 µm IR images reveals that there were a number of cloud-to-ground lightning strikes during various phases of the storm’s development, as large convective elements formed and intensified upwind of the Black Hills.

A MODIS true color image (above, viewed using Google Earth) shows the areal extent of the snow cover on 03 May 2008, as well as the locations of the heaviest total snowfall amounts: 54.5 inches (138 cm) at Lead SD, and 24.0 inches (61 cm) at Sundance WY.

A comparison of MODIS true color and false color images from 03 May (above) demonstrates how the false color imagery (which uses the MODIS 2.1 µm near-IR channel) can differentiate between snow cover (which, along with ice crystal clouds and ice-covered lakes, appear as cyan-colored features) and supercooled water droplet clouds (which appear as shades of white).

Consecutive daily MODIS false color images from 02, 03, and 04 May (below) show that the snow cover was melting rapidly under the influence of the strong May sun. The 54.5 inches of snow that fell at Lead SD had a liquid equivalent of 4.64 inches (12 cm), so the rapid snowmelt led to a quick rise of creeks and streams that caused some flooding problems.

A series of mid- to late-April MODIS true color images from the SSEC MODIS Today site (above) reveals that many of the lakes across northern Minnesota were still ice-covered as of 29 April 2008. According to the Minnesota State Climatology Office, the “ice-out” (or melting) of lakes across northern Minnesota this Spring season is delayed by about 2 weeks compared to historical normals, and this is the latest ice-out of many lakes in the region since 1996.

AWIPS images of the MODIS visible channel, 1.6 µm near-IR “snow/ice” channel, and Land Surface Temperature (LST) product (above) depicted a broad swath of heavy snow on the ground across parts of eastern South Dakota and western Minnesota on 26 April 2008. Snowfall amounts included 19.0 inches at Watertown, South Dakota (which set an all-time record for 24-hour snowfall accumulation there) and 15.5 inches at Brandon, Minnesota. On the MODIS visible image, the unfrozen lakes stand out as dark features against the bright white snow-covered ground; the snow cover appears very dark on the MODIS snow/ice image (since snow is a very strong absorber at the 1.6 µm wavelength), in contrast to supercooled water droplet clouds which appear as varying shades of white. Note how the MODIS Land Surface Temperature values within the snow swath were in the 30-40º F range (green colors), compared to much warmer LST values of 50-60º F (yellow to orange colors) over the bare ground regions on either side of the deep snow cover. The MODIS LST product gives an indication of the temperature of the actual land surface (or “skin temperature”), which can be several degrees different than the air temperatures measured in instrument shelters located about 5 feet above ground level.

A MODIS true color image from the SSEC MODIS Today site (below, viewed using Google Earth) further demonstrated the large contrast between the significant snow cover and the surrounding bare ground. According to the National Weather Service forecast office at Sioux Falls, a Trough of Warm Air Aloft (TROWAL) contributed to the heavy snow event (which forced Interstate 29 to be closed from Brookings - about 50 miles north of Sioux Falls - all the way to the North Dakota border).