Well here it is. The reason we suffer through the long harsh Midwest winter. The heat wave is here and it's here to stay.
An upper level blocking pattern will continue to push the heat and humidity into the central states. We started our long term hot a humid trend with a reading of 91 degrees in Eau Claire on Tuesday. The upper level high pressure center is cut off from the jet stream which will quite literally block systems from entering the central states and instead send them further north.
We may fall a degree or two short of that due to extra cloud cover from some overnight thunderstorms in Minnesota and a little less wind to help mix the lower levels of the atmosphere. High temps may get stuck in the upper 80's Wednesday.
Dew points will again be in the upper 60's to low 70's Wednesday which will keep it tropical and push heat indices into the low 90's. The UV-Index will sit at a 7 with the extra clouds, but it still only takes about 30 minutes to catch a burn. Don't forget the sunscreen!
The next 7 to 10 days are almost the exact same weather wise due to the blocking pattern mentioned above. Because of this we'll have a slight chance for isolated thunderstorms every day.
We need 3 things to produce thunderstorms. Lift, moisture and instability. It's obvious we have the moisture given the dew points mentioned before. The instability will often be there as the lower boundary layer gets much warmer than the air aloft. But, there is a thin layer of air in the mid levels of the atmosphere that is warmer than the air below it, but not warmer than the air at the surface.
This is called a 'cap', which stops the air from rising and thus prevents thunderstorms from forming. Unless we get the appropriate lift to get us past the threshold. In most cases this week, that's what will stop us from getting widespread thunderstorms, but a few areas may see that cap erode due to warming temperatures in those mid levels.