Verification of Probabilistic Quantitative Precipitation Forecast Forced Ensemble Hydrologic Forecasts Produced by the Arkansas-Red River Forecast Center

Probabilistic Quantitative Precipitation Forecast (PQPF) forced ensemble river forecasts have been produced by numerous National Weather Service (NWS) River Forecast Centers (RFC) for well over a decade. These forecasts were initially produced based on a need by various users of RFC hydrologic products such as emergency managers, water managers and NWS weather forecast offices for a simplified method of ensemble-like forecasts. This method took actual value amounts of precipitation for a percentage probability and fed them directly through the RFC’s hydrologic models. For years, RFCs have received mostly complementary subjective feedback of these forecasts with many users saying these forecasts have helped them to plan and prepare for hydrologic events, but no objective method was ever completed.

The Arkansas-Red River Forecast Center (ABRFC) has archived these PQPF based river forecasts for over a decade. The NWS Office of Water Prediction (OWP) Water Resource Evaluation Service (WRES) has made it possible to verify these forecasts to objectively examine their validity and find any biases that may be present. WRES was also used to verify official Hydrologic Ensemble Forecast System (HEFS) forecasts. Results of the PQPF based forecasts and its comparison to HEFS forecasts will be shown in this study. These results show that PQPF based forecasts reduced biases, encompassed greater probabilities and increased the probability of detection compared to HEFS forecasts, especially during larger events including moderate to major flooding.