© 2019 Terry Swails

COOKING UP A STORM DRIVEN COOL-DOWN...

July 20, 2019

Extraordinary moisture levels combined with very warm air combined to produce insane heat indices around the Midwest Friday afternoon. Here's the precipitable water vapor in that was measured. You can't see it but you sure can feel it!. 

These values are about twice what is normal for mid-July.

Another way to measure moisture is with dew points. Sweat from maturing corn along with the water vapor created dew points that were up around 80 in a large part of the central Midwest. Readings this high used to be a rare event but with the increased water vapor in the atmosphere the past 1-2 decades this is becoming a more common phenomena. 

At any rate, highs in the 90s and dew points around 80 sent the heat index values soaring. In this tweet from the NWS in Des Moines you can see they reached a feel-like temperature of 119.3 degrees!

Here are some of the HXreadings in my area at 4:00PM. 118 at Oelwein and 116 at Independence and Vinton.

Here's a few more readings from around the state of Iowa an hour later 

The heat will hold for much of the region another day with heat warnings in effect for my area through Saturday afternoon. They also extend into much of the eastern U.S.

The end is in sight as a cold front sinks through the Midwest Saturday night. The question is will strong storms form along the front like the ones that hit parts of Minnesota and Wisconsin Friday night. You can see the cold cloud tops of Friday evenings storms.

The boundary causing those storms sinks into Iowa towards Saturday evening. Ahead of it tropical moisture pools as evidenced by precipitable water vapor up to 2.47"

That generates high instability for storms which you can see in the CAPE (convective available potential energy) values below.. 

 

The hi-res NAM shows a line of storms coming across the central Midwest Saturday night out ahead of the front..

 

There is the possibility that some strong storms could form. The primary concerns would be strong winds and locally heavy rains of an inch or more in a very short period of time. SPC has a slight risk of severe storms over parts of Iowa, Wisconsin, and Illinois. Something to keep an eye on as Saturday unfolds

Once the storms depart high pressure builds south out of Canada and a refreshingly nice brand of weather moves in for the first half of next week. Looking forward to that. Play it cool again today and by all means, roll weather...TS

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