'A SYNOPTIC CLIMATOLOGY OF DERECHO PRODUCING MESOSCALE CONVECTIVE SYSTEMS IN THE NORTH-CENTRAL PLAINS'

摘要

Synoptic-scale environments favourable for producing derechos, or widespread convectively induced windstorms, inthe North-Central Plains are examined with the goal of providing pattern-recognition:diagnosis techniques. Fifteenderechos were identified across the North-Central Plains region during 1986–1995. The synoptic environment at theinitiation, mid-point and decay of each derecho was then evaluated using surface, upper-air and National Center forAtmospheric Research (NCAR):National Center for Environmental Prediction (NCEP) reanalysis datasets.Results suggest that the synoptic environment is critical in maintaining derecho producing mesoscale convectivesystems (DMCSs). The synoptic environment in place downstream of the MCS initiation region determines themovement and potential strength of the system. Circulation around surface low pressure increased the instabilitygradient and maximized leading edge convergence in the initiation region of nearly all events regardless of DMCSlocation or movement. Other commonalities in the environments of these events include the presence of a weakthermal boundary, high convective instability and a layer of dry low-to-mid-tropospheric air. Of the two corridorssampled, northeastward moving derechos tend to initiate east of synoptic-scale troughs, while southeastward movingderechos form on the northeast periphery of a synoptic-scale ridge. Other differences between these two DMCS eventsare also discussed.