Statistical Analysis of the Experimental Neighborhood Probabilistic Excessive Rainfall Outlook from the 2014 and 2015 Flash Flood and Intense Rainfall Experiments

Flash flooding requires accurate QPF and hydrologic information to prepare the user community for impacts. Improvement to warm-season QPF forecasting is still needed and dependent upon the expansion of high-resolution convection-allowing ensembles. Additionally, the hydrologic aspect of flash flood forecasting represents a challenge on its own as recent rainfall, soil type, slope, land use, basin size, degree of urbanization, etc., all play a role in determining the flash flood threat. This combination of meteorological and hydrologic challenges contributes to flash flooding being the deadliest weather phenomena. As the national center responsible for providing QPF and flash flood forecast guidance, NCEP's Weather Prediction Center (WPC) and the Hydrometeorological Testbed at WPC (HMT-WPC) are uniquely positioned to address the challenges associated with flash flood forecasting. WPC currently issues an operational product indicating the threat of flash floods: the Excessive Rainfall Outlook (ERO). The ERO is issued at scheduled intervals throughout the day as part of WPC's Day 1–3 QPF product suite and indicates the probability of exceeding flash flood guidance (FFG) at a point across the contiguous United States (CONUS). This product is intended to provide several days of advance notice about the potential for flash flooding.

In an effort to improve flash flood forecasts and verification both at WPC and across the NWS, HMT-WPC has conducted three years of the Flash Flood and Intense Rainfall (FFaIR) Experiment. The FFaIR Experiment brings participants from the operational forecasting, model development, and research communities together during the month of July to explore the challenges associated with flash flood forecasting. In particular, the experiments have focused on evaluating the utility of high-resolution convection-allowing models and ensembles for short-term flash flood forecasts, exploring new tools and approaches for combining meteorological and hydrologic information, and exploring improvements to WPC's operational Excessive Rainfall Outlook. Tested improvements to the experimental Excessive Rainfall Outlook issued during the experiment included lower probability thresholds of 2% and 5% to compliment the 10% and 30% contours as well as application of the neighborhood probability approach. This poster will compare the results from the previous two FFaIR Experiments (2014 and 2015) and examine the statistical calibration of the probabilistic contours in relation to the number of flash flood reports captured. Plans have already begun to produce the experimental product in parallel with the operational Excessive Rainfall Outlook during the 2016 warm season.