Formation of a Sharp Snow Gradient in a Midwestern Heavy Snow Event

Abstract

A case study of the 13?14 March 1999 heavy snow event across southern Missouri and neighboring states is presented. Of the many features that made this storm notable, the very sharp gradient on the northern periphery of the snowfall field was most intriguing. Moreover, that the snowfall field was confined to the southern half of the state resulted in snow-free regions across central Missouri where significant accumulations had been predicted. The focus of this study was thus to reveal the cause of such large snowfall gradients. Little evidence exists of convective snowfall over Missouri through 1200 UTC 14 March 1999, when this study ends. Analyses confirm that the release of neither convective instability nor conditional symmetric instability was responsible for the large snowfall gradient on the northern boundary. Instead, the juxtaposition of dry and moist airstreams from the north and south, respectively, as components of a deformation zone ultimately defined the large snowfall gradient across southern Missouri.