The 19 July 1996 Monongalia county west virginia flash flood: an insight to how future warnings may be even more precise

This paper will show how AMBER estimates of Average Basin Rainfall (ABR) were used to adjust FFG during a multiple rainfall event. This allowed early detection of a flash flood associated with warm-topped convection.

Early on 19 July 1996, a flash flood caused damage to 120 homes and 30 private bridges in Monongalia County, West Virginia. The flash flood resulted from two periods of intense rainfall. The first period of rainfall occurred during the daylight hours of 18 July, when 1-2 inches of rain saturated the ground and caused rising stream levels. Shortly after midnight on 19 July, a second period of rainfall associated with warm-topped convection produced rainfall rates of 2.5 inches an hour over the same area. Subsequent rainfall accumulated an additional inch in less than 30 minutes, resulting in flash flooding.

AMBER is a flash flood application that uses rainfall estimates from the Weather Surveillance Radar 1988 Doppler (WSR-88D) Digital Hybrid Scan Reflectivity (DHR) product to compute ABR for 3,000 watersheds and urban areas every 5 to 6 minutes. AMBER can produce ABR from both standard and tropical Z/R relationship equations. AMBER also compares ABR to the FFG produced by River Forecast Centers (RFC) to estimate the probability and intensity of flash flooding.

This case study will demonstrate how; 1) ABR estimates can be used to lower the daily FFG when multiple episodes of heavy rain occur between FFG issuances, 2) AMBER can be used to determine the proper Z/R relationship for a particular event, and 3) ABR rate can quickly alert forecasters to the onset of intense rainfall.