Wednesday, August 30, 2006

Fog inhibits diurnal convection

Today's satellite image and animation for the tri-state area of Wisconsin, Iowa, and Minnesota shows a prime example of the power of sun-heated land. There is a pool of colder air aloft in the western Great Lakes that by itself isn't enough to cause instability. But add heating from the Sun at ground level and the gradient is enough to produce convection and clouds.

A fog bank was present overnight and into the middle of the day over the tristate region, as seen in this morning image. The fog was burned off by the sun but it took until the early afternoon to do so and kept the ground cooler. Ergo, no cumulus where the fog was earlier.

This animation is during the afternoon as the bank slowly dissipated, leaving a kidney-shaped hole in the cumulus field.

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