Characterizing Warm-Season Extreme Precipitation in the HREF Means

Extreme precipitation from warm-season convection remains a well-known operational forecasting challenge. Oftentimes it occurs from high-intensity, short-duration events that can lead to flash-flooding and related impacts detrimental to life and property. Deterministic convective allowing models (CAMs) provide guidance that can be useful for anticipating these kinds of events, but can fail to represent the range of possible forecast scenarios. An ensemble of CAMs, like the NCEP High Resolution Ensemble Forecast (HREF) system provides both high-resolution guidance and forecast uncertainty information leading up to an event.

The HREF provides short-range (0–48 h) probabilistic forecasts at high spatial (~3 km) and temporal (1 h) resolution. It can provide useful guidance for high-impact and extreme precipitation events, for which the skill of deterministic CAMs is limited. In this presentation, the performance of the HREF ensemble mean, ensemble probability-matched mean (pmm), and ensemble localized probability matched mean (lpmm) precipitation forecasts will be assessed. Rainfall totals over 1- and 3-hour durations from these forecasts will be compared to observed totals from the Multi-Radar Multi-Sensor (MRMS) Quantitative Precipitation Estimates (QPE) Pass 2 during the warm-season convective months of May-September for 2021 and 2022. The results of this work may provide useful knowledge regarding how, when, and where to apply HREF ensemble-mean forecasts in anticipation of an extreme precipitation event.