Composite Soundings Associated with Severe and Tornadic Thunderstorms in Central Alberta

Abstract

Composite profiles of temperature, humidity and wind are constructed for severe thunderstorms that formed over central Alberta, Canada, during the period 1967–2000. Storms were divided into three categories consisting of 13 non-tornadic storms which produced hail ≥ 3 cm in diameter but no reported tornadoes, 61 weak tornadoes (F0 and F1) and 13 significant tornadoes (F2–F4). All three composites showed potential instability through most of the sounding. However, thermodynamic parameters did not discriminate among the three categories. In contrast, however, composite hodographs did show noticeable differences among the three groups. The hodograph for the significant tornado composite exhibited strong low-level veering winds having 0–3 km helicity of 65 m2 s−2 and southwest winds of about 20 m s−1 in the mid- to upper levels. The hodograph for the weak tornado composite showed weak low-level veering winds (0–3 km helicity of 17 m2 s−2) and much lighter winds overall compared with the other two composites. The non-tornado composite hodograph had nearly unidirectional southwest winds of about 15 m s−1 in the mid- to upper levels. The significant tornadic storms were similar to typical mid-latitude supercell hodographs.