Forecasting Extreme Rainfall and Flooding Threats at WPC (51)

Alex Lamers, NWS Weather Prediction Center, College Park, MD



The Weather Prediction Center (WPC) has a legacy of quantitative precipitation forecasting stretching back nearly 60 years, and has built expertise in forecasting extreme rainfall over many decades. Increasingly, this expertise is being delivered with a focus on impacts, such as with the Excessive Rainfall Outlooks. Of particular note, a High Risk outlook is issued when forecasters are more confident in a severe and potentially catastrophic flash flood event.

This presentation will be centered on a statistical examination of impacts from flooding on 60 High Risk days and comparing that to overall flood impacts in the contiguous United States from 2014 to 2017. A considerable portion of U.S. flood fatalities and damages have occurred on High Risk days, despite being issued on just 4 percent of days. These statistics will underscore that the Excessive Rainfall Outlook is reasonably well-calibrated to impact levels, and is a vital tool for communicating particularly dangerous flooding threats across the weather enterprise.

The presentation will also provide perspective on how Excessive Rainfall Outlooks fit into the overall information flow from WPC, examine that information flow through the January 2018 southern California flash flood and debris flow event, and mention recent and potential future enhancements to rainfall and flash flood prediction services.