Just days after the record-setting rainfall in the Chicago metropolitan area, more active weather is impacting the area. Very unstable air has allowed thunderstorms to expand across northern Illinois. These thunderstorms are making there way to the east/southeast and moving towards Chicago. The entire Chicago metro area is under a tornado watch until 1:00 AM local time. Also, a flash flood watch has also been posted. Storms are currently producing excessive rainfall totals in areas such as Rockford and Freeport, IL. These areas are under flash flood warnings as storms are “training” across the area. “Training” of thunderstorms is the meteorological phrase for describing thunderstorms that continually develop and move across the same area. This west to east band of storms is starting to show a tendency to spread east/southeast.
There is a threat for excessive rainfall across parts of northern Illinois. The ground is already saturated in many areas that were hit hard over the past week. Radar trends show the heavy rain moving east/southeast. The entire Chicago metro area will have thunderstorms increase in coverage and intensity over the next several hours.
Also of concern is the potential for these storms to begin to accelerate and transition into a severe wind threat. There is the possibility of one or two bow echos to move across this area. A bow echo is when a line of thunderstorms has the look of a bow on radar, which is a signature for severe winds. Winds of over 60mph are possible and there is also the possibility of a tornado as well. Already, the northwest side of Rockford had a measured wind gust of 80 mph!
After nighttime thunderstorms, the area will have sunny skies and hot conditions on Thursday. With the high humidity levels, the heat index value will be near 100 degrees. There is also a threat for additional thunderstorms across the area with the frontal boundary in the area. Severe weather and flooding will remain a threat.