A synoptic climatology of cool-season derecho events

Synoptic-scale environments favorable for producing derechos in the cool season (September through February) are examined with the goal of providing useful techniques for identifying commonalities within derecho activity corridors. Fourteen derechos were identified from two activity corridors located in the southeastern United States and Atlantic seaboard regions between 1986 and 1995. The synoptic environment at the initiation and midpoint of each derecho was then evaluated using surface, upper-air, and the NCAR/NCEP reanalysis data sets. Models are provided in order to illustrate the synoptic-scale environment and to assist meteorologists in recognizing conditions favorable for cool-season derecho formation. Marginal instability and strong synoptic-scale forcing characterized the environments of events in both corridors. The overall synoptic patterns associated with cool-season derecho-producing mesoscale convective systems (DMCSs) resembled environments found with cool-season tornado episodes. Recognition of key elements in this environment could lead to improvements in cool-season severe weather prediction.