A wedge of very warm air is flooding the Plains into the Upper Midwest today. This is sending temperatures into the 90s to near 100 degrees with heat indices from near 100 to 110. The map below has a mix of data from the surface to about 5,000 feet above MSL (mean sea level). Notice the southwest flow (flow from SW to NE) from Texas to Minnesota. The air is also very moist. However, little in the way of thunderstorm activity is expected in the hot air mass because of its stability. The exception will be along the cool front from Minnesota to NE Colorado where there is enough lift to overcome a strong capping inversion aloft. Thunderstorms are also possible along the warm front in Minnesota and northern Wisconsin.
The forecast map below is from the National Weather Service and is valid for June 29, 2018. Notice where severe storms are possible from Minnesota to South Dakota and Wyoming and portions of nearby states. The entire pattern will slip southeast on Saturday pushing into Iowa with heavy rain possible. By Sunday morning the cool front will extend from NW Wisconsin to Iowa and the Texas Panhandle. Thunderstorms are expected along the front with cooler air behind ending the hot spell.