The heat will be "on again" around the Midwest Thursday-Saturday. An upper level heat dome is building over Missouri and it will see to it that hot and very humid air expands over the region.
By Friday you can see PWAT's (precipitable water vapor) pooling along a near stationary front from Nebraska and NW Iowa into central Wisconsin.
South of the stationary front dew points across Iowa are shown soaring on the GFS into the upper 70s to low 80s. 82 just west of Des Moines! That is super juicy air and probably overdone. Still, it will be sultry.
By Saturday morning water vapor is nearly 200% above normal over NE Iowa.
On the high resolution GOES satellite you can see the ring of fire developing. The upper level high (heat dome) is situated near St. Louis. Skies are clear under it where the air is sinking causing it to heat up and cap the atmosphere. Over the upper Midwest clouds from Colorado to northern Wisconsin represent the northern extent of the cap. It's in that area that thunderstorms will become active the next 24-48 hours.
With time over the weekend the high pressure will weaken and retrograde allowing the ring of fire to enter my area. Scattered thunderstorms are expected either Friday night or Saturday. The convective threat will continue into Sunday before the boundary sags even further south early next week.
Models are not great at predicting where the strongest storms will occur beyond 24 hours so it's difficult to pin-point the location of the heaviest rains. However, the GFS is hinting at some very heavy totals of 3-6" near the Iowa Minnesota border. With the high PWAT's and slow movement of the forcing, it's very likely that some parts of the central Midwest will see excessive rains. It's just a matter of when and where and the answer to that is far from clear at this time.
What is certain is high humidity and warmer temperatures will make for very uncomfortable conditions Thursday and Friday, perhaps Saturday in some areas. The NAM has this for dew points late Thursday.
Here's the temperatures.
That type of heat and humidity would produce heat index's like this.
Even worse over parts of my area Friday.
Heat advisories have been issued for these areas. They will likely be expanded east.
Between the heat and weekend thunderstorms some impactful weather is on the table the next 3-4 days. For those of you weary of summer's steam, there is good news. By next Tuesday a pattern change will bring much cooler weather to the Midwest. Highs for several days may not get out of the 70s. I'm "cool" with that! Roll weather...TS