Sunday, 6 January 2013
Exhibit Hall 3 (Austin Convention Center)
On 2 March 2012, a prolific severe weather outbreak took place across the Ohio River Valley and southern United States. These storms generated 160 tornado, 469 (52 severe) hail, and 325 (10 severe) wind reports across 16 states, with the first observed tornado on record for portions of eastern KY. Unfortunately, these devastating events resulted in 40 fatalities and over $2 billion in damages (the first billion dollar weather disaster of 2012). Given the relative rarity of tornadoes in eastern Kentucky, we present a case study of an EF-3 tornado that tracked along a 49 mile stretch of land across eastern KY and affected the town of Salyersville, KY, and nearby areas. This event was analyzed using Level 2 NEXRAD radar data, Rapid Update Cycle model output via Integrated Data Viewer, and mesoanalysis data from the Storm Prediction Center. The questions surrounding why such strong tornadoes tracked across, in some cases tornado-void areas, may be addressed by analysis of the large-scale atmospheric circulation and mesoscale interactions. Specifically, a strong surface cold frontal boundary advanced upon an anomalous warm, moist sector, which was positioned across much of KY. Supercell thunderstorms quickly developed across western and central KY, where surface-based instability, effective bulk shear, and effective storm relative helicity values ranged between 1500-2000 J kg-1, 60-70 kts, and 400-600 m2/s2, respectively. As these storms propagated east, increased radar reflectivity and storm intensity from multiple storm mergers was collocated with a strengthening low-level jet across the eastern part of the state. Despite the waning convective instability, effective bulk shear and storm relative helicity maxima up to 80 kts and 800 m2/s2, respectively, were positioned in the far eastern part of the state. It is these conditions that primarily set the stage for the relatively rare and strong tornadic supercells in eastern KY on that day. Lastly, it is plausible to consider that a wedged warm front along the mountainous terrain also played a contributing role in the maintenance of strong helicity, rotating updrafts, and the resulting tornadoes.
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