Statistically this is the hottest week of the year. And right on cue here comes a wicked combination of heat and humidity that will broil the Midwest...a natural sauna. Aside from the heat, there will be periods of thunderstorms that roam parts of the region delivering strong storms and heavy rain. Overall, it looks to be a tough week in more ways than one.
If there's one element that will dominate it's the incredibly high moisture levels that are forecast. Corn is at a mature stage and transpiring (sweating) water vapor into an already tropical air mass. The annual marriage of the two will create dew points that will peak near 80 for several days.
Here's what the GFS has for dew points Thursday. Some parts of Iowa as high as 83. That's what happens in a state where 34% of the land is planted in corn!
Add some heat to the dew points and you have yourself a sauna. Here's the highs forecast by the GFS Thursday afternoon.
Why do I call it a sauna...because that's exactly what it will feel like. Check out these heat index values.
Where the highest dew points are found is where the heat index is shown reaching 117 degrees around Waterloo, Iowa and points west. Remarkable stuff!
On the edge of the heat dome where it encounters cooler air is where you find thunderstorms in what's known as the ring of fire.
The "ring" is likely to wander around northern Iowa or southern Minnesota into at least Saturday. This zone will act as the breeding ground for convective clusters that could bring strong to severe storms, especially at night. If the boundary remains nearly stationary some excessive rainfall is possible. The last 2 runs of the GFS have shown this for rains the next 7 days. Note two 8-9" bulls-eye's, one in Minnesota the other in northeast Iowa.
The 18z GFS:
The 12 GFS:
If you are up near the Iowa Minnesota border there are consistent trends of torrential rains from time to time that could produce significant flash flooding.
With all the heat that's coming (and some storms) weather service offices have been publishing story boards addressing the potential and some of the headlines. Here's a few starting with the NWS in Des Moines.
The NWS Quad Cities.
The NWS St. Louis.
The NWS Omaha.
The NWS La Crosse.
The NWS Minneapolis.
The NWS Chicago.
A great reminder from the NWS in St. Louis on why you never leave children or pets in a car. The temperature goes from 80 to 123 in an hour with the windows up.
Needless to say this is going to be a tough week and no matter where you are in the Midwest there's going to be impactful weather of some sort. Enjoy the sauna. Roll weather...TS