Characterizing Extreme Precipitation in HREF Individual Ensemble Members

The NCEP High Resolution Ensemble Forecast (HREF) system is a 10-member ensemble of opportunity, consisting of five different convection-allowing models (CAMs), plus time-lagged forecasts from each of the five the CAMs. HREF provides high-resolution (3km, 1h) probabilistic forecasts out to 48h. These probabilistic forecasts can provide guidance for high-impact events, showing the range of uncertainty in the forecast, which deterministic models alone can not convey. Given the diverse membership of the HREF, there is value in characterizing the contributions of the individual ensemble members to the forecast, particularly for high-impact events. Such an analysis may provide insight into the forecast skill and systematic errors for the HREF.

In this study, we analyze various aspects of precipitation forecasts from the individual HREF ensemble members for the summer (June, July, August) of 2022, including the distribution of hourly rain, seasonal rainfall totals, and the frequency with which each member produces the ensemble maximum precipitation. Particular attention is given to characterizing the individual member forecasts of extreme rainfall events (defined here as 1”/hour or 1” in 3 hours). Additionally, the performance of extreme rainfall forecasts are evaluated using the Multi-Radar Multi-Sensor (MRMS) QPE Pass 2 product as a reference.