Quantifying extreme rainfall threats at the Hydrometeorological Prediction Center

Flooding is one of the leading causes of weather-related fatalities in the United States. Many deaths are a result of flash flooding from extreme rainfall events. Just over the past two years, extreme rainfall has resulted in several high-impact flash flooding events, including Atlanta (2009), Nashville (2010), and Caddo Gap, Arkansas (2010). As the nation's source for quantitative precipitation forecast guidance, the Hydrometeorological Prediction Center (HPC) employs a variety of techniques to quantify the probability of extreme rainfall. The probability of extreme rainfall is primarily expressed through a probabilistic excessive rainfall outlook and experimental probabilistic quantitative precipitation product suite. Text forecast discussions supplement the graphical and gridded information. This presentation will review the techniques and data available to HPC forecasters to quantify extreme rainfall threats, and highlight ongoing activities to further improve anticipation of extreme rainfall. Particular emphasis is placed on the use of convection-allowing deterministic and ensemble model guidance, and associated post-processed fields. Case examples from recent extreme rainfall events, such as the Atlanta (2009), Nashville (2010), and Caddo Gap, Arkansas (2010) floods, will be used to show the strengths and weaknesses of current and experimental techniques.