A batch or train of thunderstorms was responsible for the Johnstown, Pennsylvania, flood of July 19-20, 1977. Close to a foot of rain fell in 24 hours over the mountains north of the city. A series of dams failed with sent a wall of water into the city. Dozens were killed and damage topped $100 million.
A similar setup mostly likely was the cause of the Smethport, Pennsylvania, record rainfall and flood of July 17, 1942. In just 12 hours, 34.30 inches of rain fell. The torrential rain caused catastrophic mudslides and flooding that took the lives of more than a dozen people.
Rounds of thunderstorms with torrential rain and gusty winds will ride the rim of heat and roll across portions of the northeastern United States into this weekend. Temperatures will climb well into the 90s F at times from the Ohio Valley to part of the mid-Atlantic for the balance of the week. While an outcome similar to that of either flood is unlikely, some communities may face flooding on a smaller scale. This could evolve into a life-threatening event.
Each batch of storms can be accompanied by multiple downpours and unleash torrential rainfall. One group of storms is likely from later Thursday into early Friday. A second batch of storms is likely from Friday night to Saturday. This batch has the greatest potential to bring significant flooding.
A third series is likely from later Saturday to Sunday. This batch is most likely to affect a broad area with perhaps less intense rainfall but isolated incidents of flash flooding. If you have outdoor plans this weekend, it is recommended that you stay up to date with your local radar and news stations.