Quantifying Precipitation Processes after the Landfall of Hurricane Harvey using Polarimetric Radar Observations

Hurricane Harvey produced over 100 cm of rain post-landfall, from 26-31 Aug 2017, to portions of southeast Texas, resulting in catastrophic flooding in major metropolitan areas such as Houston. Understanding and relating these enhanced precipitation processes to polarimetric radar observations provides operational forecasters with additional information that can be used for improving flash flooding warning decision making. Quantifying the evolution of precipitation processes that can lead to flash flooding in tropical cyclones is achievable using polarimetric radar observations from the NEXRAD WSR-88D system. This presentation aims to quantify polarimetric radar signatures, such as the evolution of the melting layer height using the co-polar correlation coefficient field, in addition to vertical columns of enhanced differential reflectivity and specific differential phase. These columns denote supercooled drops being lofted above the melting layer and are useful for detecting convective updraft evolution and associated precipitation processes. A vertical displacement of the melting layer in space and time provides insight to the extent of warm rain processes, maximizing precipitation efficiency at the surface, and can be compared throughout different quadrants of tropical cyclones. Quantifying these polarimetric radar signatures in tropical cyclones such as Harvey can vastly improve forecasting of heavy precipitation and flash flooding events, in addition to improving numerical weather prediction of extreme rainfall events and tropical cyclone evolution.