Following the recent blizzard in the Central Plains over the 12/23-12/26 period, the broad area of snow cover produced a region with relatively cold surface temperatures. When low clouds are present, their brightness temperature contrasts against the warmer land surface are reduced. Through the use of multispectral imagery and image classification, the MODIS instrument aboard Aqua or Terra can better discriminate snow cover from low clouds. In the image below, there is little contrast among the “shades of gray” across Nebraska, South Dakota, Minnesota and Iowa, although low clouds were present.
Through the use of multiple spectral bands and color enhancement, snow cover in the image below is depicted in red shades, with cloud cover in white. This color combination is able to discriminate snow from the streak of cloud cover running through the Dakotas into northern Illinois. In the northern half of Minnesota, snow cover on the ground is likely, but forested areas dominate the landscape and mask the surface snow cover in many areas. Shades of blue indicate snow-free land areas in western Oklahoma, portions of Kansas and eastern Colorado.