We've talked about this before... it's a pattern that happens in the summertime. It gets hot and humid and storms tend to form late in the day/overnight on the edge of the heat - known as the "ring of fire." It's also a difficult pattern to forecast the placement of storms.
Sunday it got hot... it got humid... again. Temperatures shot up into the 90s and dew points were well into the 70s.
Heat index values were in the triple digits across much of the Upper Midwest. Of course this created a lot of instability. CAPE (convective available potential energy) values - the amount of instability in the atmosphere was incredibly high.
Storms rolled quickly out of Minnesota and a line barreled through eastern Iowa and Illinois. Strong winds (upward of 70 mph) led to roofs being ripped off in some cities.
The basis of the ring of fire starts with an area of high pressure in the upper levels of the atmosphere.
The heat builds under this ridge at the surface and up above our heads. The warm air above our heads creates what's called a "cap." A cap suppresses convection - stops clouds from growing up high in the sky and creating thunderstorms. A few things can happen to break the cap and lead to storms. Temperatures at the surface can get incredibly warm and lead to storms. A boundary (outflow boundary, cold front or warm front) can come in and lead to storms (as was the case Sunday).
This does make it difficult to determine where and when storms will form. This is also why most of the storms in this pattern happen late in the day or overnight. And due to the high instability storms are usually strong in this pattern.
This is a look at the next two days on the high resolution NAM. The storms may stay north of my local area on Monday with storms firing up on Tuesday afternoon.
The ring of fire pattern will start to break down some toward the middle of the week, too.
As that happens the storm track with shift south and there will be periods of storms through the rest of the week and into the weekend.