Another storm is on the way and will bring heavy rain and the potential for strong storms through the day Monday. Rain will begin late Sunday night and spread across Iowa into Illinois into Monday morning. There will be a lot of moisture in place for heavy rain and several boundaries at play that will lead to the potential for strong storms. Here's the projected surface analysis on Monday afternoon:
The area of low pressure will travel across Iowa and into Illinois. Close to the low there will be the potential for strong and even rotating storms. The thing that is keep the severe weather threat low is that rain will be likely though the day, so surface instability will be low. Here's an animation of the storms from the hi-resolution NAM:
The clouds and rain will hold temperatures down in the Upper Midwest and instability at the surface will be lower as a result. High temperatures Monday -
Instability over Iowa and northern Illinois will be sufficient for thunderstorms, but the greater instability will be down to the south.
The dynamics of this will drive the severe threat on Monday. Near the triple point (where the low, cold front and warm front meet) there will be a lot of wind shear (spin) in the atmosphere. This would allow for rotating storms that could produce strong winds or even isolated tornadoes.
The latest Storm Prediction Outlook has the greatest chance in southern Illinois and in the warm sector out ahead of the cold front. However, this may shift further west depending if there are any breaks in the rain and clouds. That would allow for more destabilization the severe risk would be greater.
The main component of this system will be the high moisture and heavy rain potential. Widespread rain, of around an inch will be likely in Iowa with locally higher amounts possible.
Behind the rain, high pressure moves in Tuesday and fall-like air moves into eastern Iowa. Temperatures will be below normal and the humidity will drop. Temperatures will be around 10 degrees below normal in the 60s and 70s.
It will feel a whole lot nicer outside for much of the week. But first some summer weather with high humidity and the potential for some strong storms Monday.