A synoptic climatology of cool-season derecho events

Synoptic-scale environments favorable for producing derechos in the cool se ason (September through February) are examined with the goal of providing u seful techniques for identifying commonalities within derecho activity corr idors. Fourteen derechos were identified from two activity corridors locate d in the southeastern United States and Atlantic seaboard regions between 1 986 and 1995. The synoptic environment at the initiation and midpoint of ea ch derecho was then evaluated using surface, upper-air, and the NCAR/NCEP r eanalysis data sets. Models are provided in order to illustrate the synopti c-scale environment and to assist meteorologists in recognizing conditions favorable for cool-season derecho formation. Marginal instability and stron g synoptic-scale forcing characterized the environments of events in both c orridors. The overall synoptic patterns associated with cool-season derecho -producing mesoscale convective systems (DMCSs) resembled environments foun d with cool-season tornado episodes. Recognition of key elements in this en vironment could lead to improvements in cool-season severe weather predicti on.