EF1 tornado in Washington County, Pennsylvania

A tornado produced sporadic damage along a 14.5 mile path beginning near Houston, PA and finally dissipating 24 minutes later in Finleyville, PA. The initial damage occurred near Allison Hollow Road, where large limbs were broken from hardwood trees. The tornado continued east, uprooting trees along Irwin Avenue before crossing Locust Avenue and Walnut Street in Houston, where large hardwoods were snapped and softwoods were uprooted. Shingles were removed from several homes, a lamppost was bent, a stop sign left leaning, and a large metal porch awning was removed from the back of a home. This area was where peak intensity (estimated wind speed of 90 MPH) was observed before weakening near the Chartiers-Houston Junior/Senior High School.

The circulation periodically weakened and reintensified along the remainder of its path. Notable damage was observed along Linden Creek Rd where wheat was laid over, a barn lost shingles, and a narrow path of damage to hardwood trees was found. The circulation paralleled Venetia Rd where sporadic tree damage was observed. Modest intensification occurred near Finleyville where a few uprooted and snapped trees were observed, and a three story apartment building lost siding on its western face. The tornado dissipated close to Pennsylvania Route 88.

An occluding surface low slowly drifted across Ohio on May 21st. Bands of showers with embedded thunderstorms moved across southwest Pennsylvania. During the mid to late afternoon, one convective band, associated with ample 0-3km CAPE and surface vorticity, was able to generate four tornadoes across southwest PA. Three were relatively brief and weak, but one longer-track EF1 was noted in Washington County. Multiple rounds of slow-moving heavier rain also produced a number of flash flooding incidents.