Mild temperatures lead to heavy rainfall and storms
Spring-like temperatures will lead to spring-like thunderstorms Tuesday. A stationary boundary in place Monday will continue to sag south through northern Illinois this afternoon. Low pressure will develop in the Plains later tonight lifting the front back north as a warm front after midnight. Temperatures will rise overnight close to 50° by the time you wake up Tuesday. Showers and thunderstorms will also occur early Tuesday morning with heavy rainfall possible. We'll see a brief break in the storm activity during the afternoon but thunderstorms, some strong to severe, will redevelop as a strong cold front plows through the Midwest by Tuesday night. With such a large amount of moisture in place heavy rainfall will be the main threat for northern Illinois and southern Wisconsin. Totals may exceed three quarters of an inch to over an inch of rainfall by Tuesday night. While significant flooding isn't expected, some runoff may occur if soil temperatures remain below freezing. Right now soil temperatures between 4" and 8" deep remain between 29° and 31°. If totals exceed over an inch, which they may if thunderstorms move through, then flooding may become a bigger concern.
Once the front passes Tuesday night temperatures will drop significantly with highs Wednesday only in the middle 20s.