Skies begin mostly sunny Sunday morning as cloud cover from downstate thunderstorms overnight move out. Temperatures will warm quickly, from the 60s in the morning into the low to mid 80s by the afternoon, despite winds turning to the north and northeast.
The majority of the day will be dry and warm, although there are a few showers moving across northwest Iowa that could restrengthen as the move east. If this occurs, we could see a few showers and isolated thunderstorms move across south-central Wisconsin mid-afternoon.
The threat for severe thunderstorms does exist for northern Illinois and southern Wisconsin later Sunday evening. That threat, though, may be a little more conditional based on the interactions between a back-door cold front, warm front, and outflow boundaries.
Thunderstorms will develop over Iowa and northern Missouri ahead of low-pressure late Sunday afternoon. These storms are expected to quickly turn severe as they move east and southeast. A warm front over northern Illinois will become the focal point for the storms to ride along during the evening and overnight. This warm front will also interact with old outflow boundaries from overnight storms, and an incoming back-door cold front off of Lake Michigan.
An enhanced risk for severe weather remains in place for Iowa and northern Missouri, as well as extreme west-central Illinois. A slight risk for severe storms is in place for counties southwest of Winnebago county: Jo Daviess, Ogle, Lee, Carroll and Whiteside. Here is how our storm potential looks going into the evening and overnight:
Showers moving through northwest Iowa Sunday morning have been weakening, but there has also been some redevelopment along the southern edge. It does look like these may hold together as they move east towards the Stateline. If so, there is a small chance (20%) that an isolated storm or two could occur over south-central Wisconsin. Later in the day the focus will shift to the thunderstorms that are expected to develop over southern Iowa. As these storms move east, they could take a slightly more southeast turn, following better instability and outflow boundaries south of I-80. If that does happen, this is where the highest risk for severe weather would be. If, however, we see more of an easterly track then the severe storm threat would increase for parts of northern Illinois. Our greatest risks would be strong winds and large hail.
Heavy rainfall is also a concern as moisture surges northward giving us the potential for several rounds of thunderstorms. This would push totals over an inch in some locations by Monday morning, with a few spots coming close to two inches.
The forecast for Sunday evening/night remains a tricky one and will be heavily dependent on how things evolve to our west. Be sure to stay updated with the forecast throughout the afternoon and evening.