"A flash flood forecasting system has been developed which combines distributed modeling and statistical analyses to produce gridded forecasts of return periods. A distributed hydrologic model (DHM) coupled to a threshold frequency (TF) post-processor, DHM-TF, is currently being tested over Baltimore/Washington (LWX), Binghamton (BGM), and Pittsburgh (PBZ) Weather Forecast Office (WFO) domains, running in real-time on each WFO's server. It has verified well against National Weather Service (NWS) flash flood warning areas, local storm reports, and USGS gauge-based flood data. The development, prototype implementation, and evaluation of DHM-TF have been strongly collaborative efforts involving OHD, the PBZ, BGM, and LWX WFOs, OHRFC, MARFC, NERFC, and CBRFC. Comprehensive evaluation of real-time and retrospective DHM-TF simulations shows that, while not without shortcomings, the system is generally able to correctly depict the placement and timing of flash flood events, and offers several advantages over current operational NWS flash flood forecasting tools. These include a non-binary assessment of flood severity, high-resolution gridded output, routing of river flow, the inclusion of a snow model, and the potential for rapid updating and sub-HRAP resolution operations"--Abstract.

National Weather Service (NWS)

United States