Synoptic Parameters as Discriminators between Hailfall and Less Significant Convective Activity in Northeast Colorado

Abstract

Synoptic data are studied to determine which, if any, parameters representing large-scale physical processes can be used to discriminate effectively between days of insignificant convective activity and those with significant moist convection and high hail potential in northeast Colorado. Divergence, relative vorticity, vorticity advection, temperature advection, surface mixing ratio and a modified K index (George, 1960) were computed and associated with observed weather. Two methods were used to compare distributions of these parameters for their discriminative potential. The first involved ranking of the Student's t statistics for both hail versus no-hail and significant versus insignificant convection stratifications. The second method was a graphical technique for plotting cumulative relative frequencies of the stratified distributions. The most effective parameter on a comparative basis for discriminating between significant and insignificant convection was a measure of low-level and middle-level tropospheric moisture content. Moisture content at the surface provided the best discrimination between hail and no-hail.