A Baseline Climatology of Sounding-Derived Supercell andTornado Forecast Parameters

Abstract

All of the 0000 UTC soundings from the United States made during the year 1992 that have nonzero convective available potential energy (CAPE) are examined. Soundings are classified as being associated with nonsupercell thunderstorms, supercells without significant tornadoes, and supercells with significant tornadoes. This classification is made by attempting to pair, based on the low-level sounding winds, an upstream sounding with each occurrence of a significant tornado, large hail, and/or 10 or more cloud-to-ground lightning flashes. Severe weather wind parameters (mean shear, 0-6-km shear, storm-relative helicity, and storm-relative anvil-level flow) and CAPE parameters (total CAPE and CAPE in the lowest 3000 m with buoyancy) are shown to discriminate weakly between the environments of the three classified types of storms. Combined parameters (energy-helicity index and vorticity generation parameter) discriminate strongly between the environments. The height of the lifting condensation level also appears to be generally lower for supercells with significant tornadoes than those without. The causes for the very large false alarm rates in the tornadic/nontornadic supercell forecast, even with the best discriminators, are discussed.

Some aspects of the international climatology of tornadoes by damage classification

“…With population increases and growth of urban areas since many of those events, the possibility of a large-fatality tornado cannot be ignored. 1905-1996, 1998-199 , Goliger et al 1997 …”

An investigation of local and national NWS warning outbreaks for severe convective events.

“…In an analysis conducted by Rasmussen and Blanchard (1998) of 51 soundings that were in close proximity to EF2+ tornadoes, the upper quartile for 0-6-km bulk shear was 21-29 m s-1 (42-56 kt), while the upper quartile for mixed-layer CAPE was 1,877-3,028 J kg-1. Using these ranges to indicate high instability and shear environments, 3 of 10 local events and 7 of 10 national events could be classified as having high CAPE and shear.…”

Numerical simulation of the heavy rainfall caused by a convection band over Korea: a case study on the comparison of WRF and CReSS

“…Many references based on the analysis of both observations and simulations suggest that the existence of MAUL is evidence of strong convective activity (Choi et al 2011). When looking at the convective available potential energy (CAPE), the values from both simulations were not as large as the typical magnitude that is required to develop an environment conducive for the convective storm (e.g., CAPE [ 1000, Djuric 1994;Weisman and Klemp 1982;Rasmussen and Blanchard 1998). This indicates that the saturated and unstable environment seen in both simulations is not critically dependent on the buoyant energy available to accelerate a parcel vertically.…”

“…This different behavior clearly reflected the storm-relative environmental helicity (SREH), which is shown to be a measure of the potential for updraft rotation in a storm (Blanchard 2011;Davies-Jones et al 1990). The SREH (126 m 2 s -2 , negative sign-turning counterclockwise) produced by CReSS is much higher than that of WRF (19 m 2 s -2 ) and is actually above the median for the criteria of the convective supercell classified by Rasmussen and Blanchard (1998). Therefore, CReSS formed a more favorable environment for upward advection of warm and moist air at the lower level.…”