Utilizing Dual Polarization Instantaneous Precipitation Rate to Predict Flash Flooding

Dual polarization radar uses an algorithm 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, research shows that potential flash flood events may be easier to detect when compared to traditional radar interrogation techniques. This study focused on events from both Buffalo (KBUF) and Cleveland (KCLE) radars during the convective seasons between 2015 and 2017. Radar data was examined in order to identify cases where DPR exceeded the threshold noted above for 20 minutes or more over the course of an hour. 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 duration. Results showed that a DPR of 2”/hr for 35 minutes or 3”/hr for 25 minutes are good indicators for potential flash flooding within areas that have at least a moderate FFPI. Rainfall rates over 4 inches an hour, although impressive from a precipitation rate standpoint, usually don’t last long at one location. These rates therefore showed less skill since they did not provide much lead time and may be prone to hail contamination. Research results show the potential for increased detection and lead time for flash floods. This research has aided forecasters with detection and lead time for flash floods and future research may support the use of this product in all NWS offices.