How Is Extreme Precipitation Manifesting during the Warm Season? Reflections on 4 Years of the Hydrometeorological Testbeds' Flash Flood and Intense Rainfall Experiment

Doswell et al (1996) stated: “It rains the most where it rains the hardest for the longest”. Breaking that down, it rains the most where the extremes occur. While duration might be the secret to the most precipitation, its the extreme rates that drive the accumulation. Showing how often and where the extremes occur has been performed by many authors over the last 30 years. MCS and tropical systems lead the way in generating precipitation extremes and recent work by James and Schumacher (2024) has shown that these 6h extremes correspond better to flash flood reports.

In the HydroMeteorological Testbeds Flash Flood and Intense Rainfall (FFaIR) Experiment we have been forecasting overnight extremes in warm season precipitation within 6h temporal windows. Extremes have been found in this temporal duration to be above 5” in maximum rainfall using the Multi-Radar Multi-Sensor system. This 5"/6h threshold corresponds to what is produced operationally in the High Resolution Ensemble Forecast system in terms of probability of exceedance. And yet, our perceptions of the precipitation extremes' correspondence with flash flood reports is lower. Situating our perception with data from the last 4 warm United States Warm seasons is our goal.

In this presentation we will explore how precipitation extremes have manifested over short time scales while looking at a few thresholds and temporal windows to characterize individual events and seasons. The ultimate goal is to further understand the relationship between heavy rain and flash flooding, and the various ways these events emerge.