A Proposed Microburst Nowcasting Procedure Using Single-Doppler Radar

Abstract

Thirty-one microburst-producing storms from northeast Colorado were studied using single and multiple Doppler radar for the purpose of identifying radar signatures that indicated the development of a downdraft capable of producing a microburst. Descending reflectivity cores, increasing radial convergence within cloud, rotation and reflectivity notches were found to be microburst precursors, appearing typically 2?6 min prior to initial surface outflow. Descending maximum reflectivity cores coincident with increasing radial convergence within cloud (3?8 km AGL) or near cloud base is believed to be a good indicator of storm downdraft and microburst predictor, especially when coupled with low ?e air above cloud base and a dry adiabatic lapse rate below cloud base. Three conceptual models have been drawn, based on the 31 events, to summarize the radar signatures of importance in low, moderate, and high-reflectivity microburst-producing storms. Experience indicates that Doppler radar may aid in providing 0?10 min nowcasts of microbursts. This requires the rapid perusal and assimilation of a large quantity of radar data by the forecaster. To improve upon this effort, a forecaster-computer environment is proposed to allow the forecaster to readily view radar reflectivity and Doppler velocity information in both unprocessed and analyzed form. Use of multi-image radar displays and time-height profiles of quantitative radar estimates of reflectivity and radial shear are suggested to provide an environment where rapid progress can be made in developing techniques to nowcast microbursts.