Black Hills Above the Clouds

April 25, 2007


Referred by: Lee Grenci, Department of Meteorology, Penn State University
Summary authors & editors: Lee Grenci, Steven Seman

The loop of visible satellite images above the northern Great Plains was taken on March 19, 2007 (from 1345Z to 2045Z). Note the area of cloudiness over western Nebraska, the western Dakotas and eastern Montana. The general lack of texture in the clouds suggests a bank of stratus. Observe that there's an apparent hole in the stratus over western South Dakota. Actually, it's really not a hole. Indeed, this loop of images suggests that the "hole" is simply the higher elevations of the Black Hills (more than 7,000 feet or 2,134 m) poking their "heads" above the stratus.

To confirm this analysis, check out the 12Z soundings (click on link below), at Rapid City, South Dakota, which show the local variation of temperature (in red) and dew points (in blue) with altitude. Note, near 850 mb (about 5,000 feet or 1,524 m), the thin layer in which temperatures approximately equal dew-point temperatures. Here, the relative humidity is close to 100%. This saturated layer marks the extent of the relatively thin layer of stratus. As a result, higher elevations in the Black Hills were above the stratus deck.

Thanks also to David Babb for his help with this.

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