Temperatures Tuesday warmed into the middle and upper 80s, but the heat index made it feel more like 100 degrees in a few locations. That humidity will continue to climb Wednesday and Thursday before a cold front moves in Thursday evening bringing an end to the late summer heat. The timing of the front, however, Thursday could put a little wrench in the forecast for both the high temperature and heat index temperature.
A warm front moving through the Stateline Tuesday evening will continue to lift north, passing into Wisconsin Tuesday night. This will result in temperatures Tuesday night only dropping into the mid-70s. As winds increase from the southwest Wednesday afternoon temperatures are expected to warm into at least the mid-90s. Dew point temperatures, however, will remain in the upper 70s pushing heat index temperatures over 100 degrees. Heat index temperatures will range from 105-115 degrees during the afternoon. Little relief will come at night as overnight lows remain in the mid to upper 70s.
While Wednesday will likely remain dry, there is a small chance for an isolated thunderstorm during the afternoon. As the strong ridge of high pressure begins to slowly sink to our south Wednesday, a very subtle upper-level disturbance will move through Iowa and into northern Illinois. It’s possible that this could be enough to break the cap we will have in place Wednesday, giving us the isolated storm chance. If that occurs, temperatures would not be quite as hot or humid. But with that chance remaining low, the going forecast will hold for now. Excessive heat warnings are in place for both Wednesday and Thursday.
Thursday will likely be another hot and humid afternoon, but a cold front moving in from Wisconsin and down Lake Michigan could not only keep temperatures down in some locations, but it could also bring in a chance for a few strong/severe storms during the late afternoon and evening.
As of Tuesday evening, it looks like the front will come through after 6pm/7pm Thursday leaving enough time during the day for temperatures to warm back into the mid-90s. If, however, the cold front speeds up then highs wouldn’t be quite as hot, or humid, and our there would be a slightly higher chance for a few stronger storms during the afternoon. Should severe thunderstorms develop, damaging downburst winds would be the greatest threat.