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Daryl Ritchison, WDAY, Published July 21 2012

Weather Talk:

On Friday, the thermometer at Hector International briefly reached 100 degrees. Both North Dakota State University and the cooperative observer recorded a high of 99, and the Moorhead airport hit 97. Yet the high at Jamestown and Grand Forks was only 92, in Fergus Falls 91 and Wahpeton 90.

In meteorology, there are many different levels of influence on the weather: the macro scale (hemispheric), the synoptic scale (low pressure and corresponding fronts), micro scale (urban influences) and meso scale (an event that may occupy a few counties, which was the case Friday). That afternoon, a weak wind shift line (trough) stalled just to the west of Fargo-Moorhead, the downward momentum (subsidence) ahead of that feature allowed drier air from aloft to slowly sink to the surface, lowering the dew point. Plus, that downward motion compresses the air, which increases the temperature. Those two factors among possibly others combined to heat a small area near the metro and eastward another 5-10 degrees more than other locations nearby. It was yet another reason the weather continues to fascinate and challenge me at the same time.

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