Oklahoma Downbursts and Their Asymmetry

Abstract

Doppler radar data collected each spring in 1979?1984 with the two Doppler radars operated by the National Severe Storms Laboratory (NSSL) are used to investigate the asymmetry of low-altitude divergent outflows of convective storm downbursts in central Oklahoma. Outflows in Oklahoma storms can be highly asymmetric with horizontal shear along the axis of maximum divergence as much as 5.5 times the shear along the axis of minimum divergence. The downbursts observed in central Oklahoma, all large-scale (4?10 km) events, were superposed with the maximum reflectivity core of the storms. However, scanning strategies may have precluded detection of smaller scale (>4 km) microbursts. Typical downbursts observed during the Joint Airport Weather Studies (JAWS) Project were of small scale (>4 km) and were often associated with little or no rain at the surface. The mechanism for the initiation of the majority of JAWS microbursts was evaporative cooling, which occurred when precipitation fell into a dry, deep and nearly adiabatic boundary layer it appears that other mechanisms are responsible for the initiation of the observed Oklahoma downbursts because of a lower cloud base and a moister and slightly more stable boundary layer.