Why is it so muggy?

From meteorologist Bill Endersen:

If you think that it’s gooier out there than a Louisiana crawdad boil, then you are right on target. As I write this Monday afternoon, it is hotter and more humid in the Twin Cities and the surrounding area than it is in New Orleans.

An Excessive Heat Warning, based on the combined effects of heat and humidity, is in effect for all or parts of 11 states from the Dakotas through Minnesota to Wisconsin and south to Oklahoma until Wednesday night.

The dew point, the temperature to which air must be cooled to become saturated with moisture, is an excellent measure of the amount of moisture in the air. The current dew point is 77 degrees which is way up there in the uncomfortable range. The record highest dew point for the Twin Cities is 81 degrees, first set on July 30, 1999 and which was matched Sunday evening.

Why is it so muggy? It started with a plume of sub-tropical moisture that worked its way up through the Great Plains and then spread across Minnesota. A stagnant weather pattern is keeping the moisture in place. Recent heavy rainfalls have helped as well.

Usually during high dew point events, the dew point drops during the daytime thanks to mixing of drier air from aloft. Today some of the rain that fell recently, including the 3.73 inches that I measured in my backyard Friday thru Friday night, has been evaporating from the wet ground and has pushed the dew point up nastily from the 70 that was reported at 6 a.m.

Look for dew points to drop quite a bit beginning later on Thursday. Until then, feel free to join the youngsters in the wading pool.

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