A case-by-case study of the Significant Tornado Parameter and non-tornadic supercells

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Sunday, 17 January 2010
Exhibit Hall B2 (GWCC)
Sarah M. Glenn, NOAA/NWS, Norman, OK

Much research has been conducted about the most favorable environments for the formation of significant tornadoes; however, many situations exist where tornadoes do not materialize. This causes the false alarm ratio to be high even though shear and instability parameters would indicate a high chance for tornado formation. In various instances, storm modes quickly become linear rather than discrete, although this is not always the case. Little is understood about the reasons for the occurrence of these “null” cases, and these “environmental failures” will be the focus of the study.

A database will be created of situations where the Significant Tornado Parameter (SIGTOR), calculated by the Storm Prediction Center, would indicate a high potential for tornadoes to form, but no tornadoes were reported within a mesoscale proximity area (within 300 miles and 6 hours of the favorable region). Only situations with the largest SIGTOR values covering a sufficiently large spatial extent for non-tornadic events will be examined. This list of cases will be further narrowed by collecting archived mesoanalysis graphics to check for continuity of the SIGTOR parameter values to then eliminate cases with more isolated grid points. Archived national and regional radar data will be investigated to determine thunderstorm mode and either select or reject the case.

For each of the final selected null cases, archived Level II NEXRAD data for will be collected and viewed in GRLevel2. Surface observations, satellite imagery, observed soundings, and RUC soundings will also be collected for each event and explored. This should provide for an overview of the environmental conditions surrounding each non-tornadic event, and further analysis may then occur.