Snow-covered Black Hills surrounded by stratus cloud

March 19th, 2007 |


The effect of the topography in western South Dakota and eastern Wyoming was very obvious on 19 March 2007, as low-altitude stratus clouds were forced to move around the higher elevation portions of the Black Hills (GOES-11 visible images: Java animation). AWIPS images of a few of the MODIS channels (above) revealed that a good deal of the cloud-free highest elevations were still snow-covered. This snow cover appeared brighter than the surrounding tree-covered (but snow-free) surface on the Band 1 visible image (above, upper left panel) — the darker appearance of that same area on the Band 7 Snow/Ice image (above, lower left panel) is a signal of snow on the ground (in contrast to the supercooled water droplet stratus cloud, which appeared much brighter on the Band 7 image). MODIS and GOES fog/stratus product images from the pre-dawn hours showed that this area of stratus cloud was forming due to upslope northerly/northeasterly flow in the wake of a cold frontal passage.

A 500-meter resolution MODIS true color image (below) showed even better detail of the snow cover and the stratus clouds that surrounded the Black Hills. The light gray region just to the east of the stratus cloud edge is the Badlands National Park, whose sandy and rocky surface has a higher albedo than the surrounding grasslands. Snow depths at the highest elevations were still as great as 18 inches at North Rapid Creek (station NRPS2, near Rochford, South Dakota).
MODIS true color image