A weakening complex of thunderstorms early Monday left behind a couple of outflow boundaries across northwest Illinois. As the morning activity weakened, and eventually faded away, additional thunderstorms were quick to develop in a northwest to southeast line, stretching across Carroll, Ogle and Lee counties. As the storms moved southeast, they were quick to strengthen prompting a severe thunderstorm warning for portions of Lee and Ogle counties. The strong winds did cause some damage to trees northwest of Nelson (Lee County) around 3pm, and produced a 46 mph wind gust in Dixon. Isolated thunderstorms continued across parts of Ogle, Boone and DeKalb counties, but weakened quite a bit as they moved east. Skies will remain mostly clear through the evening with temperatures rising back into the low to mid 80s before only cooling off into the low 70s overnight.
Thunderstorms are then expected to redevelop overnight as an upper level disturbance moves out of the Rockies and across the Plains, closer to northern Illinois by 2am/3am feeding off of the higher moisture and instability that’ll be in place. The risk for severe weather remains low tonight but any storms that do develop will be capable of producing heavy downpours through the morning.
Those storms should be moving out by mid-morning Tuesday, but additional thunderstorms may develop during the afternoon; similar to what some experienced Monday afternoon. Any storms that do develop would be isolated in coverage, but contain very heavy rainfall and potentially gusty winds.
High temperatures Monday fell shy of the forecast high of 90 degrees thanks to the cloud cover and afternoon thunderstorms. The same *could* happen for Tuesday and Wednesday if storms redevelop during the afternoon. If not, afternoon high temperatures will rise into the low 90s with the heat index reaching the triple digit mark, if not low 100s for a time during the afternoon.
Right now the forecast calls for highs reaching 92 degrees both Tuesday and Wednesday, with the heat index ranging between 100-107 degrees. Any thunderstorms that develop during the afternoon the next couple of days would be capable of producing gusty winds, hail and torrential rainfall.
A cold front coming through late Wednesay night will only briefly bring a break from the humidity as it is set to return back north as a warm front Thursday and Friday.