Extended Abstract (120K)5.3
Development of warning criteria for severe pulse thunderstorms in the Northeastern United States using the WSR-88D
Carl S. Cerniglia, NOAA/NWSFO, Seattle, WA; and W. R. Snyder
Recent research has resulted in improved identification of, and establishment of more accurate warning criteria for well organized convective systems such as derechos, tornadoes and supercell thunderstorms in the northeast United States. Overall, there has been steady improvement in National Weather Service lead times and warning verification. However, a significant percentage of events that are not warned for, or events with very short lead times, are less organized, scattered and largely of the "Pulse" type of storm.
Lemon developed effective techniques for identifying severe Pulse storms, which were widely used from the late 1970s to early 1990s. These methods relied on manually tilting the radar beam through the storm using the Range Height Indicator (RHI) scope of those radars, and identifying the elevations of the reflectivity cores of various Video Integrated Processor (VIP) levels. The WSR-57S and WSR-74S radars had approximately 2 degree beam widths which were much coarser than the WSR-88D's 0.95 degree beam width. The deployment of the WSR-88D rendered these techniques obsolete due to the much narrower beam width, and automated scanning strategy.
This study's objective was to improve warnings for Pulse type storms, and
identify WSR-88D products, thresholds, and methods that would be useful in the
Northeast United States. It also sought to determine whether refinements of
Lemon's techniques would serve as valid warning criteria on the WSR-88D. In this
study, over 500 thunderstorms from 1995-1998 over the northeast United States
were identified and interrogated using WSR-88D Archive II data. Grid VIL, Cell
VIL, Maximum Reflectivity, Maximum Reflectivity Height, Echo Top, Storm Top,
Storm Speed and Direction, Storm Volume, VIL Density, Probability of Hail (POH),
Probability of Severe Hail (POSH), and the top and of 45 dBz, 50 dBz, 55 dBz, 60
dBz and 65 dBz reflectivity levels were correlated with severe storms and a set
of non-severe control cases. Several of these parameters showed significant
promise as warning criteria. To a remarkable degree, the concepts of Lemon's
earlier work were validated on the WSR-88D. The parameters with the greatest
promise as warning criteria in the study were, the combination of maximum dBz and
maximum height of that dBz value, VIL Density, POH, and POSH. Utility was also
established for some other WSR-88D products.
Session 5, Radar Applications
Tuesday, 13 August 2002, 10:30 AM-12:00 PM
Previous paper Next paper