Wind Profiler Observations Preceding Outbreaks of Large Hail over Northeastern Colorado

Abstract

Wind profiler, rawinsonde, and surface observations of the atmosphere over northeastern Colorado during the morning hours on 44 days were compared to the severity of subsequent thunderstorm activity. On half of thes days, large hail (diameter ≥2 cm) was observed over the region, while on the other half, only thunderstorms with no large hail or other severe local storm phenomena were reported. Statistical comparisons revealed that the wind speed near 8 km above ground level (AGL), the southerly wind component between 2.0 and 2.5 km AGL, and a thermal advection index computed from the degree of wind veering in the 1.5?2.5-km layer, were all significantly greater on the large-hail days than on the nonsevere weather days. Concurrently available rawinsonde observations did not detect some of these differences as clearly as did the profiler observations. A screening discriminant analysis of possible predictor combinations showed that the optimum discrimination between the cases with and without large hail was given by a linear combination of 8-km wind speed from profiler measurements and positive buoyant energy from rawinsonde temperature profiles.