Predicting severe hail in the WFO LWX County Warning Area: toward increased accuracy in hail size forecasts

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Wednesday, 20 January 2010
Matthew R. Kramar, NWSFO Baltimore/Washington, Sterling, VA; and J. Waters

Handout (849.0 kB)

One of the challenges in National Weather Service warning operations is differentiating radar reflectivity signatures for hail from those of very heavy rain, and subsequently identifying hail size from reflectivity patterns. This issue becomes even more complicated when storms are located over sparsely populated areas, which makes real-time confirmation of conditions nearly impossible.

Studies in this regard have already been conducted with positive results for the Northern Plains and for the Southern High Plains. Atmospheric freezing levels and storm reflectivity core heights (greater than or equal to 50dBZ) as determined from WSR-88D data were correlated in consideration of reported hail size with subsequent operational success, with the primary statistical differences believed to be a result of regional atmospheric variability (i.e. presence of an elevated mixed layer, moisture content, etc.).

No comparable study has been conducted for the Mid-Atlantic region. The present study seeks to establish such a statistical database of severe hail events for the Mid-Atlantic region. Using methods developed by Donavon and Jungbluth, RAOB soundings from Sterling, VA and surrounding forecast offices, reflectivity data from nearby WSR-88D radars, and Storm Data reports from WFO Sterling will be used to establish comparable seasonal statistics for anticipated hail size for Mid-Atlantic region thunderstorms. This study's results are expected to better enable warning meteorologists to anticipate hail-size diameter and aid in warning decision-making with greater confidence (especially in light of potential changes to severe thunderstorm hail diameter criteria), thereby increasing average warning lead time.