Poster Session P6.6 Using maximum storm-top divergence and the vertical freezing level to forecast hail size

Tuesday, 28 October 2008
Madison Ballroom (Hilton DeSoto)
Joshua M. Boustead, NOAA/NWS, Topeka, KS

Handout (459.8 kB)

The use of storm-top divergence from Doppler weather radar has proven useful for the issuance of convective weather warnings, especially in anticipation of severe hail. Relationships were developed in the 1970s and 1980s to help operational forecasters in predicting the maximum size of hail from the strength of the observed storm-top divergence. A new study was conducted using high-resolution velocity data from the National Weather Service's WSR 88D to investigate the relationship between storm-top divergence and hail size. Thunderstorms included in the study were from the 2003 to 2008 convective seasons. In addition, numerical model data from the National Center for Environmental Prediction's Rapid Update Cycle model were used to obtain the height of the freezing level in the convective environment. Relationships were then developed using storm-top divergence with a range of freezing level heights to predict a corresponding hail size. Average lead times were also calculated to the maximum hail size from the time of the strongest divergence signature. Finally, verification of the results was conducted using data from the Severe Hail Verification Experiment (SHAVE) where high resolution hail reports were used in conjunction with Doppler radar data.
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