Pro-FLASH: A Probabilistic Framework for Flash Flood Warning in the United States

We demonstrate the concept of a probabilistic framework for flash flood forecasting over the Conterminous United States (CONUS). The framework is referred to as Pro-FLASH, which is based on the next generation tools for flash flood warning in the National Weather Service: the Multi-Radar Multi-Sensor (MRMS) and Flooded Locations and Simulated Hydrograph (FLASH) systems. Pro-FLASH is part of the Forecasting a Continuum of Environmental Threats (FACETs) framework of the National Severe Storms Laboratory (NSSL). Pro-FLASH comprises a cascading of independent probabilistic models for 1) hydrologic forecasts, 2) impact-based flooding thresholds and 3) exposure and vulnerability. In this presentation, we feature the grid-based threat probabilities and impact-specific information that Pro-FLASH is capable of producing in response to FACETs’ new warning paradigm. The results we present are based on a 10-year re-analysis of hydrologic estimates over a 1-km grid covering CONUS. The construction and validation of the probabilistic model for hydrologic forecasts is done with a sample of over 2000 gauged basins. Local Storm Reports (LSRs) are employed to address the verification challenge at ungauged locations. LSRs are specifically utilized to assess the skill of the grid-based probabilities and impact-based flooding thresholds to identify areas of threat. Case studies are focused on vehicle-related impacts, which are the most common during a flash flood event.