CHICAGO — The National Storm Prediction Center has included the entire Chicago area in a marginal Risk of severe thunderstorms Friday and Friday night (see dark-green-shaded area on the Friday severe weather outlook map above). West-central Illinois is included in a stronger Slight Risk area that extends back west into Missouri (yellow-shaded area on the map above)
Clusters of showers/strong to possibly severe thunderstorms are expected during the next 24 hours as a cold front lies west-east through northern Illinois into southern Lake Michigan. The warm moist very unstable air mass in place will be conducive to storm development with the most likely occurrence during the afternoon into the overnight hours.
While damaging winds and large hail are possible, the stronger storms will have a greater likelihood of heavy flash-flood-producing downpours over already saturated soils.
A Flash Flood Watch is in effect for most of the Chicago area from this Friday evening and overnight hours into Saturday morning.
Rain is expected to let up somewhat this morning – then clusters of showers and thunderstorms are expected to redevelop this afternoon and evening along a cold front that will be lying west-east across northern Illinois and southern Lake Michigan. Low pressure moving along the front from the central plains will pass through Chicago later at night. Intense heavy rainfall over already saturated soils will likely cause additional flash flooding in harder-hit areas.