A synoptic climatology of derecho producing mesoscale convective systems in the North-Central Plains

Synoptic-scale environments favourable for producing derechos, or widesprea d convectively induced windstorms, in the North-Central Plains are examined with the goal of providing pattern-recognition/diagnosis techniques. Fifte en derechos were identified across the North-Central Plains region during 1 986-1995. The synoptic environment at the initiation, mid-point and decay o f each derecho was then evaluated using surface, upper-air and National Cen ter for Atmospheric Research (NCAR)/National Center for Environmental Predi ction (NCEP) reanalysis datasets. Results suggest that the synoptic environment is critical in maintaining de recho producing mesoscale convective systems (DMCSs). The synoptic environm ent in place downstream of the MCS initiation region determines the movemen t and potential strength of the system. Circulation around surface low pres sure increased the instability gradient and maximized leading edge converge nce in the initiation region of nearly all events regardless of DMCS locati on or movement. Other commonalities in the environments of these events Inc lude the presence of a weak thermal boundary, high convective instability a nd a layer of dry low-to-mid-tropospheric air. Of the two corridors sampled , northeastward moving derechos tend to initiate east of synoptic-scale tro ughs, while southeastward moving derechos form on the northeast periphery o f a synoptic-scale ridge. Other differences between these two DMCS events a re also discussed. Copyright (C) 2000 Royal Meteorological Society.