Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Thursday November 13, 1997
Figure 2 shows the GOES-9 derived reflectivity product. The red arrow points to the same region over northeast Colorado. In this image it becomes clear that the "white" region in Figure 1 is part liquid water ( a good reflector of 3.9 micrometer solar energy ) and part snow ( a poor reflector of 3.9 micrometer solar energy ).
One must exercise caution, however, notice how dark central Idaho appears in Figure 2. Is this snow on the ground? Figure 1 shows that there is no visible snow on the ground. Dark regions in the reflectivity can also be due to certain types of surface vegetation. This futher supports multichannel analysis for detecting snow on the ground.
Although not shown here, image loops are also helpful in detecting clouds over snow covered ground, as the clouds will move, but the snowfield will not. You may see melting in the snow cover, however. Of course, being aware of a region's recent weather history, recent snow in this case, will indicate when you may need to make a snow/cloud distinction.