An Interesting Satellite Image

One of the many tools that forecasters at the Chicago NWS office use are infrared satellite images, which show images of clouds based on their temperature.  Sometimes, however, the satellite image shows the difference in temperature for objects other than clouds.  In the case below, there is an interesting darkening over much of northwestern Iowa, signifying ground that is warmer than the "lighter" areas in Iowa, Illinois and Wisconsin.  Air temperatures over the two areas vary little, suggesting something else is influencing the ground temperature.  Further investigation showed that the darker area corresponds very nicely with the part of Iowa that saw very little rainfall in the past week.  Because the sun's energy does not have to go into evaporating moisture, but instead is used to directly heat the surface of the earth, the soil in this part of Iowa is significantly warmer than in areas that saw rainfall earlier in the week.  One can also see that Lake Michigan is much lighter in this picture because of the 40-50 degree water temperatures!



Note the darker area over northern Iowa, signifying warmer soil temperatures.  Also note that air temperatures (in green)

vary little across the area. 


This image, showing the rainfall over the past 7 days across Iowa, shows a distinct area of northwestern Iowa that saw little

rainfall.  This area matches very well with the darker region seen in the above satellite image.

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