Utilizing Dual-Polarization Instantaneous Precipitation Rate to Predict Flash Flooding

The WSR-88D dual polarization radar creates a product called Digital (instantaneous) Precipitation Rate (DPR) which can be useful in predicting flash flooding. When re-processed to estimate the duration for which areas meet a minimum threshold of two, three, and four inches per hour respectively, initial research shows that potential flash flood events may be easier to detect when compared to traditional radar interrogation techniques. Heavy rain events from 2015-2017 between 10 and 120 km of the Buffalo (KBUF) and Cleveland (KCLE) radars respectively were examined to find coherent cases where DPR exceeded each rain rate threshold for 20 minutes or longer. A total of 1710 cases were then compared to observed flash flood events. These cases were categorized further based on a location’s vulnerability to flash floods through the use of a local static Flash Flood Potential Index (FFPI) and stratified by rainfall rate and how long the heavy rain lasted during a 60 minute time period. The FFPI identifies areas more prone to flooding due to urbanization and steep terrain. Results showed that for areas at least moderately susceptible to flash flooding that the risk increases significantly when instantaneous precipitation rainfall rates of at least 2 inches per hour last more than 35 minutes, or when rainfall rates of at least 3 inches per hour last more than 25 minutes. Rainfall rates over 4 inches an hour showed less skill since they did not provide much lead time and may be prone to hail contamination. This research is currently being used by two National Weather Service (NWS) offices and has aided forecasters with detection and lead time of flash floods. Future research may support the use of this product in all NWS offices.