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Out of phase

Posted at 8:17 AM on October 8, 2008 by Craig Edwards

Did you notice how quickly the clouds cleared eastern Minnesota after the rain ended? If you were out and about at the lunch hour you also noticed the temperature in the Twin Cities dropped from 61 degrees to the middle 50s. The cool front, clearly recognized by the abrupt wind shift to the north moved through at late morning.

In this fluid, layered atmosphere, meteorologists are challenged by the dynamics that produce precipitation and clear skies. On Tuesday, the mid level trough of low pressure, creating lift to produce rain, moved into western Wisconsin by late afternoon. On satellite imagery, you could view the sharp back edge of the cloud line, only about twenty miles behind the rain shield.

Meanwhile, at the surface, the wind shift line was about six hours out in front of the mid level trough or wave. Thus, meteorologists would refer to the rain which occurred on Tuesday as mainly post-frontal, or out of phase with the noticeable surface front.

Rochester set a new daily record for October 7th, with a total of 1.62 inches of precipitation.
CE

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