Synoptic features leading to the development of the most severe tornado recorded in recent times in southwest Australia are discussed. In accord with previous experience the salient causative factor in the occurrence of non-summer cyclonic-type tornadoes in this region is shown to be the simultaneous advection of warm moist air from the Indian Ocean in the lower levels and cold, dry, southerly air of polar origin at a higher level. The critical relation of these conditions to the vertex of a trailing V-shaped front at the boundary of interaction is emphasized and, in retrospect, it is shown how modification of the previous sounding in the light of the anticipated changes in air masses may lead to a quantitative assessment of tornadic development.
R.L. Southern (Thu,) studied this question.
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