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

Abstract

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

Climate extremes in the United States: recent research by physical geographers

“…Bentley, Mote, and Byrd (2000) found that the presence of a weak thermal boundary, high convective instability, and a dry low-to-mid-tropospheric layer facilitates derecho formation in the north-central Great Plains. Similarly, Ashley, Mote, and Bentley (2007) showed that moisture, instability, and wind shear enabled by the large-scale setting are associated with derechos.…”

Butterflies and bow echoes: addressing poor forecasts with ensemble simulations

“…This synoptic set-up and event evolution, with the MCS of interest moving parallel to a zonal surface front, is similar toFig. 4inBentley et al (2000), associated with derechos.…”

Multiscale Upstream and In Situ Precursors to the Elevated Mixed Layer and High-Impact Weather over the Midwest United States

“…Composite analysis of eight heat wave events by Bentley and Stallins (2008) illustrates that on these days, elevated surface dewpoint temperature anomalies . 38-58C are commonly associated with synoptic patterns and thermal profiles characterized by a strong capping inversion (e.g., 700-hPa air temperatures .…”

“…The sensible weather impacts from heat wave events and organized MCSs are both collectively influenced by enhanced low-level moisture (e.g., Kunkel et al 1996;Bentley et al 2000). Across the upper Midwest, the ; shaded according to scale), and wind vectors (reference at top right of panel) for the 99 warm-season EML days at MPX at 1200 UTC (e.g., day 10).…”

“…The upper Midwest United States is frequently affected by 1) warm-season convection (e.g., Metz and Bosart 2010) that may lead to severe weather (e.g., Johns and Hirt 1987) and heavy precipitation (e.g., Ahijevych et al 2004) and 2) periods of elevated surface air temperatures and dewpoint temperatures that may lead to heat waves (Bentley and Stallins 2008;Duffy and Tebaldi 2012). These two high-impact weather phenomena occurred during 30 June-2 July 2011 in the presence of an elevated mixed layer (EML; e.g., Carlson et al 1983) that influenced the development of a heavy-rain-producing mesoscale convective system (MCS) over Lake Michigan on 30 June-1 July 2011; a severeweather-producing MCS over Minnesota, Iowa, and Wisconsin on 1-2 July 2011; and record warmth over the upper Midwest between 30 June and 2 July 2011 (Figs.…”