Earlier today, Rusty posted the story below (half way down the page.) It highlighted the snowcover across the Upper Midwest. You may have noticed how hard it was to discern the difference between a cloud and the background snowcover.
The tracking of low clouds across a snowcover can be challenging for meteorologists during the day. The image below is a great example.
In the image, there is a large area of clouds over a snowpack across Wisconsin. But, it is difficult to distinguish between the two. During the day, although solar reflection makes low, stratiform clouds bright on GOES Satellite visible images, it is difficult to distinguish low clouds from adjacent ground snowcover or dense cirrus overcasts. GOES satellites take many images in many different wavelengths...the Visible and Infrared Red spectrums are the most popular. The shortwave channel often gives a superior delineation of low clouds on images because water droplets produce much higher reflectances than ice clouds or ground snowcover. Taking it a step further, when we combine the longwave channel, with the shortwave channel we can derive other satellite images that can distinguish low clouds from the background at any time of day or night.
The loop below is a great example. The first image is the visible image you see above. The next image is an 11um-3.9um derived image. Notice how it makes the clouds stand out from the snowcover. The clouds are bright white while the icy snowpack turns dark. It's magic!
The GOES visual satellite picture this morning showed us where snow still covered the ground over the Midwest. IN the 815 am CST image below you can see snow-covered terrain over southern Wisconsin and far northern Illinois, as well over southern Michigan.
Click on image for larger version.
In central and northern Minnesota are blobs of solid white. These are ice-covered lakes surrounded by darker evergreen forests.
Nearly ice-free Lake Michigan and Lake Superior show up as a darker color.
On the back side of mid-level clouds over western Iowa and southern Minnesota you can see the dark shadow of the clouds on the earth's surface.
In eastern North Dakota and the Red River Valley are more clouds moving in from the nortwest. These clouds are the leading edge of the weather system that will drop southeast across the Great Lakes Region tonight through Thursday.