Putting CAM QPFs in Context: New HRRR Heavy Rainfall Diagnostics for Flash Flood Situational Awareness and Forecasting

Abstract:

Forecasters tasked with predicting the likelihood of flash flooding across the United States (US) are often overwhelmed with the sheer volume of forecast guidance available, particularly in the current era of convection-allowing models (CAMs) and ensemble forecasts. As the first operational CAM in the US, the High-Resolution Rapid Refresh (HRRR) is often used for short-term forecasting; however, it is important to put CAM quantitative precipitation forecasts (QPFs) into a climatological and hydrological context. In this talk, we describe recent work funded by a Hurricane Supplemental project to develop gridded comparisons of HRRR QPF with several static and dynamic precipitation thresholds. HRRR QPFs are compared with NOAA Atlas 14 Average Recurrence Interval (ARI) precipitation thresholds, as well as River Forecast Center Flash Flood Guidance (FFG), in order to highlight forecasts where HRRR QPF is climatologically anomalous or potentially exceeds ground infiltration capacity. In addition, the new operational HRRRv4 predicts 15-minute rainfall accumulation, which highlights regions of extreme rainfall rates which are a concern in arid or mountainous regions, or urban areas.