CHICAGO FACES NEW FLASH FLOOD THREAT AS ‘TROPICAL-LIKE’ AIRMASS SPANS IOWA TO PENNSYLVANIA . (PHOTO).

Chicago faces new flash flood threat as ‘tropical-like’ airmass spans Iowa to Pennsylvania 

Another day of scattered heavy thunderstorms within a “tropical-like” air mass on Saturday has renewed the threat of flash flooding across several states from Iowa to Pennsylvania, including Chicago and the outskirts of Pittsburgh. 

These storms are developing along a nearly stationary front that borders a massive heat dome, which has been causing extreme heat across much of the nation this week. While the heat dome contracted Saturday to mainly impact the coastal Southeast and mid-Atlantic with triple-digit temperatures, thunderstorms forming along its edge are drawing energy from a highly unstable and moist atmosphere.

Although the chance of severe weather remains low, some thunderstorms could produce rainfall rates up to 2 inches per hour and may stall or move repeatedly over the same areas. Similar storms caused significant flooding in South Chicago on Friday, dumping 4 to 6 inches of rain in just a few hours. 

This led to flooded roads and underpasses and multiple water rescues in the southern suburbs. The ground remains saturated from earlier rains, increasing vulnerability to flash flooding with even moderate rainfall. A Level 2 out of 4 flash flood threat has been issued for much of the stationary front stretching from northern Missouri and southern Iowa through northern Illinois and Indiana, extending into western Ohio, including the Chicago area. Western Pennsylvania, including areas east of Pittsburgh, is also under a heightened flood risk. Flood Watches remain in effect for northern Iowa, Chicago, and northern Illinois. As the heavy rain chances move toward the mid-Atlantic and Northeast on Sunday, the risk of flash flooding will lessen, although cities like New York, Philadelphia, and Washington, D.C. can expect afternoon thunderstorms with only low-end flood and severe weather risks.