Abstract
All tornado reports across the contiguous United States from 2003-2011 were filtered for the maximum damage rating on an hourly grid with 40-km horizontal spacing. Convective mode was assigned to each grid-hour tornado event via manual examination of full volumetric WSR-88D data, and supercell-related environmental parameters accompanied each grid-hour tornado event from the hourly objective analyses calculated and archived at the Storm Prediction Center. Only tornado events associated with right-moving supercells (RM) or quasi-linear convective systems (QLCS) were considered in this work, which resulted in a sample of 8837 tornado grid-hour events.
 Spatial distributions of supercell-related parameters were constructed for the RM and QLCS tornado events. Sample sizes were increased by accumulating tornado events within a 120-km neighborhood to each 40-km grid box. All neighborhoods with ≥10 events were retained for percentile rank distributions of the supercell-related parameters, and then smoothed using a Gaussian kernel with a 120-km influence radius. Regional variations in buoyancy and lifting condensation level (LCL) are apparent-RM tornadoes are more common with greater buoyancy and higher LCL heights across the Great Plains compared to the Mississippi Valley region. QLCS tornadoes tend to be focused across the Ohio and Mississippi Valleys, in environments with weaker buoyancy and lower LCL heights. Vertical wind shear parameters are typically well within the parameter space associated with tornadic RM for both the RM and QLCS tornado events. The significant tornado parameter shows improved discrimination between weak and significant RM tornadoes, compared to individual kinematic or thermodynamic parameters.
Highlights
The characteristics of near-storm environments have been elucidated by several studies of observed soundings near reported THOMPSON ET AL.08 September 2013much attention in recent years has focused on convective mode and its influences on severe thunderstorm and tornado events
Artifacts of our analysis procedure are illustrated by the sharp gradient in MLCAPE across southern Manitoba (Fig. 2e), the apparent decrease in MLLCL heights from east to west across the central Rockies (Fig. 4e), and the belt of lower 0–6-km bulk wind difference (BWD) values outlining the international borders and Gulf and Atlantic coasts (Fig. 6e)
MLCAPE is clearly greatest across the Great Plains in tornadic right-moving supercell (RM) environments, with the largest values often 3000–4000 J kg–1 or larger
Summary
The characteristics of near-storm environments have been elucidated by several studies of observed soundings near reported THOMPSON ET AL.08 September 2013much attention in recent years has focused on convective mode and its influences on severe thunderstorm and tornado events. Specific storm modes, including tornadic and nontornadic supercells, were part of the Thompson et al (2003; hereafter T03) and Thompson et al (2007) proximity sounding studies, which relied on short-term forecast model soundings in close proximity to radarobserved supercells. These studies focused on discrete storms only and were somewhat limited by sample size. Building on this previous work, Smith et al (2012) created a convective mode database for a very large sample of severe thunderstorm and tornado events (22 901 total) over a 9-y period across the CONUS. The large sample of near-storm environmental data allowed for seasonal comparisons of tornado environments by
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