A preliminary dive into the climatology of the High Resolution Ensemble Forecast (HREF) heavy rainfall probabilities

WPC Forecasters look at high rainfall rate probabilities like 2-in/1-h or 5-in/6-h to help determine hazards associated with heavy rainfall and flash flooding risk for products such as the Excessive Rainfall Outlook (ERO). However, we do not know how common or large these probabilities can be and if they correspond to actual events. Here we will begin to explore a preliminary climatology of these heavy rainfall probabilities.

We will take a look at rainfall exceedance probabilities from version 3, implemented in January of 2021, of the High Resolution Ensemble Forecast (HREF). The 40-km neighborhood maximum ensemble probabilities evaluated were from the operationally generated HREF Production Probability files. We evaluated how often the ensemble system identifies a chance to exceed 2-in/1-h or 5-in/6-h compared to Multi-Radar Multi-Sensor Gauge Corrected precipitation observations. By doing this we hope to provide forecasters with the necessary context with which to apply the extreme precipitation probabilities in a real time forecasting environment.