Cloud cover will slowly increase through the night Friday as a cold front comes in from the west. Ongoing thunderstorms moving into Minnesota and Iowa Friday night will continue to move east, but weaken as they near the Mississippi River. This is the result of a ridge of high pressure located over southern Wisconsin and northern Illinois. We could see a few showers and isolated thunderstorms around sunrise Saturday, through mid-morning, but a lot of the rain will be quickly fading.
As the cold front begins moving through the Stateline, an increase in showers and isolated thunderstorms will be possible early afternoon. Skies will most likely have a bit more cloud cover during the day, limiting some of the instability for thunderstorms to really grow. A few stronger storms may occur just east of the immediate area, more late afternoon and evening, as the cold front moves towards Lake Michigan.
Skies will begin to clear following the cold front Saturday evening with a much drier air mass moving in. This will bring temperatures Saturday night down into the low 60s and pave the way for a very comfortable Sunday.
The pattern, then, may turn a little more active next week as a strong ridge of high pressure builds across the south. This will place the outer edge of the jet stream very close to the Midwest beginning next Monday. At the surface, a warm front will begin lifting through Illinois into Wisconsin Monday and Tuesday. Thunderstorms will be possible as the front pulls through. With the jet stream close by we may see several disturbances move through. Each disturbance (mini low) that passes could help enhance the risk for thunderstorms, especially at night.
However, if the storms move through during the day then the chance for temperatures reaching the low 90s would be lowered. If the storms move through during the night then afternoon high temperatures will warm well into the 90s with a heat index reaching, or surpassing, the triple digit mark. This could last for several days next week.