The 700–500 mb Lapse Rate as an Index of Microburst Probability: An Application for Thermodynamic Profilers

Abstract

This study validates the predicted association between frequency of dry microburst occurrence and large temperature lapse rate. In applying lapse rate trend data and high time resolution data from remote sensors, we first compared lapse rates from the Denver rawinsonde with the thermodynamic profiler and obtained linear correlation coefficients ranging from .63 to .94. Continuous 20-minute radiometer samples of lapse rate were available throughout the experiment period. The data indicate a critical value of 700?500 mb lapse rate ≥8°C km?1 for dry microburst occurrence. Also, we found dry microburst occurrence in the Denver area better correlated with late afternoon lapse rates than with early morning lapse rates: 67% of dry microbursts occurred with 1200 UTC lapse rates ≥8°C km?1, while 89% of dry microbursts occurred with 2200 UTC lapse rates ≥8°C km?1. We recommend that remote sensor temperature retrievals such as with Radio Acoustic Sounding Systems (RASS) extend to at least 3 km AGL to aid dry microburst nowcasting and forecast verification.