Flash Flood in Butler County, Pennsylvania

Local citizens reported severe flooding near Main Street in Zelienople as well as basement flooding.

Mid-level westerly flow of 45-70kts streamed over the Great Lakes/Upper Ohio Valley. A shortwave trough embedded within this zonal flow entered the region and moved eastward throughout the day, helping to provide forcing for ascent and strengthening of deep layer shear. Mid-level westerly flow of 45 to 70 knots also streamed over the Great Lakes and the Upper Ohio Valley. Large hail was supported by mean layer CAPE of 1500 to 3000 J/kg and effective bulk shear of 35 to 50kts. Additionally, strong synoptic winds and steepening low-level lapse rates increased the severe wind threat.

With high precipitable water values of around 1.5 inches, training storms were also able to produce localized flooding.

The hail from this event was so severe that windows in homes broke and cars were damaged. A local car dealership said that from the time of the incident to the end of September they were booked with car repairs due to hail damage. Roughly, the damage from hail for this event cost at least 12 million dollars.

The town of Zelienople, PA was hit hard with rain, as a total of 4 to 5 inches accumulated in just a few hours. As a result, the Connoquenessing Creek rose throughout the night and crested at just over 15.3 feet on Wednesday morning, May 29th. Based on historical crests, this was the 4th highest crest on record; records go back to the early 1920s.