Johnstown-Western Pennsylvania Storms and Floods of July 19-20, 1977

Professional Paper 1211
Prepared jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration
By: , and 



Widespread thunderstorms associated with two major squall lines, moved across Pennsylvania between the afternoon of July 19 and morning of July 20, 1977. The western part of outflow boundary produced by the second line became almost stationary in western Pennsylvania and resulted in 6 to 9 hours of nearly continuous thunderstorms. More than 6 inches of rain fell over a 400-square-mile area during this period. In the hills just north and east of Johnstown, rainfall totals were as much as 12 inches. Flash flooding was severe as the storms moved slowly southeastward across the Allegheny, Susquehanna, and Potomac River basins. Peak natural runoff rates greater than 1,000 cubic feet per second per square mile were common for streams draining up to 10 square miles. At eight gaging stations, recurrence intervals for the peak discharges were estimated to be 100 years or more. In addition to high surface runoff, some disastrous flooding also resulted from the failure of seven earthfill-gravity-type dams. At least 78 deaths were attributed to the flooding and eight persons were still listed as missing 1 year later. Total damages in the eight-county flood area were extremely high, possibly exceeding $500 million.

Study Area

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Johnstown-Western Pennsylvania Storms and Floods of July 19-20, 1977
Series title Professional Paper
Series number 1211
DOI 10.3133/pp1211
Year Published 1982
Language English
Publisher U.S. Geological Survey
Contributing office(s) Pennsylvania Water Science Center
Description vi, 68 p.
Time Range Start 1977-07-19
Time Range End 1977-07-20