Research on 
Pulse Severe Storms

Presentation at the Second Northeast Regional Operational Workshop

Development of Severe Thunderstorm Warning Criteria for Pulse Severe Thunderstorms in the Northeastern United States.

Although pulse severe thunderstorms account for a small percentage of severe storm related deaths, injuries and damage, they are generally considered more difficult to effectively warn for due to their short life cycle and isolated nature. This difficulty is evident when looking at warning verification scores for severe thunderstorms. Scores for pulse severe storms are generally lower than those for large, well organized convective events. Earlier work to develop warning criteria (Lemon 1980) for pulse severe thunderstorms was successful in improving these scores when the NWS was using the WSR-57, WSR-74C and WSR-74S radars. However, many of these techniques can not be directly translated to the WSR-88D, due to differences in scan strategies, beam resolution, system sensitivity and display properties (dBZ vs VIP levels).

The focus of this study is to try to develop criteria that will allow the warning meteorologist to distinguish between pulse thunderstorms that may become severe, verses those that will not. Due to the short lived nature of these events, many parameters will be examined with an eye toward gaining the maximum amount of lead time possible. To accomplish this, a data-set is being assembled of pulse thunderstorms from across the Northeast for the years 1995 through 1998. WSR-88D, Level II archive data was used in order to have the ability to create cross-sections and view the highest resolution data possible. Future investigation will include the examination of high resolution satellite data and cloud to ground lightning information in an attempt to increase warning lead time.

Storms must meet fairly strict criteria to be considered for this study. Storms displaying any organized structure, such as being aligned along fronts or squall lines, having supercell characteristics, producing tornados or having a mesocyclone present, were not included. Control cases also need to complete their life cycle over a region with a high enough population density to minimize the chance of having an undetected severe event, included as a control case. The intent behind these strict criteria is to capture the storms that are the most difficult to warn for. However, these criteria have limited the number of storms available for this study.

The presentation will show some preliminary results of the radar derived differences between severe and non-severe pulse storms. Average lead times for calculated parameters indicates that some of the currently used WSR-88D products offer little if any useful lead time for many of these events. Preliminary analysis of storm cross sections does indicate some potentially useful differences between storms that become severe and those that do not. Severe pulse storms generally develop relatively higher reflectivities, at higher altitudes, earlier in the life of the storm when compared to non-severe storms.

Evolution of a Pulse Severe Thunderstorm (right side of cross sections) and a non-severe pulse thunderstorm (left side of cross sections).   The bottom (right) frame was taken at the time severe weather was occurring. 

      non-Severe              Severe