Extended Abstract (432K)11.9
A multi-platform approach to forecasting supercell tornado potential
Angela D. Lese, NOAA/NWS, Springfield, MO; and W. D. Browning and D. T. Cramer
The false alarm rate (FAR) for tornado warnings issued by the National Weather Service has hovered between 75 and 80 percent for over 20 years, and reducing the tornado FAR is a top priority. This paper examines a non-tornadic supercell event over southwest Missouri on 22-23 April 2004 and shows the importance of using a multi-platform observational approach when forecasting tornado potential.
Recent research has shown that three key ingredients are needed for supercellular tornadogenesis: (1) a persistent, rotating updraft, (2) enhanced storm-relative helicity, (3) and a relatively warm rear-flank downdraft (low dewpoint depressions in the near-storm environment). All of these ingredients appeared to be present on the evening of 22 April 2004 over southwest Missouri. On that evening, several long-lived supercells tracked across the region, and two of these storms showed tornadic characteristics, including very strong and persistent mesocyclones, weak-echo regions, hook echoes, and reports of wall clouds and funnel clouds. Multiple tornado warnings were issued; however, no tornadoes formed.
Reanalysis of this case shows that the storms were likely slightly elevated, being north of a warm front in a relatively stable near-surface air mass. Widely-spaced surface observations to the north and south of the supercells showed that a warm front was positioned somewhere in the vicinity of the storms; however, with the lack of an available mesonet and resultant higher resolution data, the widely-spaced surface observations were not adequate in locating the front with any precision. Radar-indicated density discontinuities were not noted near the front, and while the KSGF WSR-88D VAD wind profiler showed a thinning near-surface layer of easterly winds in the stable layer, it failed to give a clear picture as to the location of the warm front relative to the supercells. Through further investigation, an important discovery was found using the visible satellite imagery early that evening. Stable wave clouds existed over southwest Missouri to the Arkansas state line, indicating that the surface warm front was about 20 miles south of the track of the supercells, and that the supercells were indeed elevated.
Session 11, Atmospheric Observations
Thursday, 13 January 2005, 1:30 PM-5:00 PM
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