Johnstown-western Pennsylvania storms and floods of July 19-20, 1977
- 1 January 1982
- report
- Published by US Geological Survey
Abstract
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 disasterous...Keywords
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