Temperatures warmed into the mid and upper 80s, low 90s, Wednesday afternoon following the non-severe thunderstorms that moved through during the morning. Heat index values have also gone up, reaching the mid-90s thanks to dew point temperatures reaching the upper 60s and low 70s. Dry conditions will remain for the rest of the evening, but the chance for showers and thunderstorms will begin to increase during the overnight.Severe thunderstorms tied to a couple storm complexes over the Plains will continue to move east through the evening, impacting the Stateline early Thursday morning. Storm coverage is expected to expand through Iowa, moving closer to the region after 2am/3am. While some of the energy needed for strong to severe storms will decrease through the night, enough will be present to hold on to the chance for a few stronger wind gusts with any of the storms that move through.
The storm threat will last through 9am, with drier conditions expected by late morning and early afternoon. Breaks in the cloud cover will allow temperatures to warm back into the mid and upper 80s, with heat index values reaching the mid-90s once again Thursday afternoon.
An incoming low-pressure system (currently over the Plains Wednesday evening) will move into southern Wisconsin Thursday afternoon. Instability will once again increase ahead of the low allowing thunderstorms to redevelop after the 2pm/3pm time frame. With just enough instability in place, and likely outflow boundaries left over from the morning activity (think of these as little mini cold fronts), some of the storms could turn strong to severe later in the afternoon. Because of that the Storm Prediction Center has placed most of north-central Illinois under a 'slight risk' for severe storms, primarily with a hail and wind threat.
Heavy rainfall will also be a concern given the high amounts of moisture in the atmosphere, but the risk for flooding will remain low. The storm threat will come to an end Thursday night as low pressure moves across Lake Michigan. We may still see a few lingering showers, and isolated storms, Friday but drier conditions are expected into the weekend.
Temperatures won't cool off much as we remain in the mid and upper 80s. Highs could even approach 90 degrees once again Saturday.