Forecasting and Communicating Record Rainfall Amounts: “What's another 5 inches? (179)

Jennifer McNatt, NWS Southern Region Regional Operations Center, Fort Worth, TX

Derek Giardino, West Gulf River Forecast Center

Patrick Burke, NWS Weather Prediction Center

Melissa Huffman, Weather Forecast Office Houston

Jonathan Brazzell, Weather Forecast Office Lake Charles

 

Abstract:

Hurricane Harvey was the most significant tropical cyclone rainfall event in United States history, both in area impacted, overall impacts and peak rainfall amounts (since reliable rainfall records began in the 1880s). When Harvey re-formed in the Gulf of Mexico on Thursday, August 24th (about 40 hours prior to landfall), the initial event total maximum rainfall forecast was for 20&rdquo in southeastern Texas. These rainfall forecasts were gradually increased to a peak of 40&rdquo several hours before Harvey made its first landfall along the central Texas coast, roughly 24-36 hours before the extreme rains began in the Houston metro area. These totals were further raised to 50&rdquo about a day before the center of Harvey left Texas.

In the days leading up to landfall along the middle Texas coast, the Weather Prediction Center, NWS offices along the Texas and Louisiana coasts, as well as NWS personnel deployed to state and local locations, were tasked with the difficult position of forecasting and communicating historic Quantitative Precipitation Forecasts (QPF). This presentation will detail the unprecedented collaboration efforts expended by these groups to ensure consistency across all levels of the National Weather Service, will show the evolution of this rainfall forecast, and also display some examples from the personnel deployed and results of briefing these record amounts. &ldquoWhat's another 5 inches&rdquo comes from one collaboration call in the day leading up to the historic rainfall in the Houston metro area. Offices were discussing maximum amounts with the Weather Prediction Center and, as one forecaster put it, once we passed 40 inches in the forecast, &ldquoWhat's another 5 inches?&rdquo.