A 15 yr climatology of derecho-producing mesoscale convective systems over the central and eastern United States

Abstract

A 15 yr (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000) climatology of derecho-producing mesoscale convective systems (DMCSs) is presented in order to better delineate their spatial and temporal patterns. Several significant results emerged from the analysis, including the development of the NW flow corridor as the dominant derecho activity region in the climatology. Results suggest that, as the sample size of DMCSs increases (230 events), the prominent derecho activity corridors across the eastern US become located in the northern Plains through the Ohio Valley, with a secondary maximum in the southern Plains. Evidence further suggests that climatological factors strongly control the distribution of derechos. For example, an anomalously strong 500 hPa height gradient existed coincident with the northern US derecho activity corridor. Another aspect of derecho development is related to the temporal distribution. Evidence suggests that derecho systems tend to occur in groups or 'families', several events occurring within several days. The synoptic environment also appears to be responsible for activating these corridors and providing an environment conducive to DMCS grouping. KEY WORDS: Derecho · Climatology · Mesoscale convective systemsResale or republication not permitted without written consent of the publisher Clim Res 24: 129-139, 2003 warm season anticyclones appears to favour and subsequently activate some derecho corridors, particularly in the Great Plains and northern tier of the US. Once synoptic-scale conditions are favourable for DMCS development, the DMCSs, after being initiated by localized forcing, tend to group or 'train' over a similar geographic region. In other words, a specific region may experience a series of DMCSs over successive days. DATA/METHODOLOGYThe primary data source for this investigation is the Storm Prediction Center's Severe Plot 2.0 software (Hart 2000) containing a database of severe convective wind events (≥ 26 m s ) and documented wind-damage reports, taken from the NOAA publication Storm Data. In order to assure consistency, the identification criteria used in BM98 is also used in this investigation (Table 1). The derecho events were then mapped to facilitate visual inspection and ensure temporal and spatial continuity. Individual wind damage reports from each derecho event were then gridded on an 1°× 1°grid-cell domain using the Interactive Data-common Language (IDL) so that contours could be generated in order to discern the geographical and frequency distribution of DMCSs.Composite reflectivity values obtained from radar archives were also examined to ensure convective characteristics of many cool-season (September-February) DMCSs. These images were obtained from the National Climate Data Center's (NCDC) on-line radar archive (available at http://lwf.ncdc.noaa.gov/oa/ radar/radardata.html).Data from the NCEP/NCAR reanalysis were used to reconstruct the 500 hPa environment during months of DMCS activity. The reanalys...

On the episodic nature of derecho-producing convective systems in the United States

“…Initially, the dataset presented by Bentley and Mote (1998) and Bentley and Sparks (2003) was employed to establish 230 derecho occurrences for the period 1986-2000. The derecho dataset in the Bentley and Mote (1998) and Bentley and Sparks (2003) studies was derived from the US Storm Prediction Center's (SPC's) on-line database of severe convective wind gusts and the SPC's SeverePlot software (Hart, 1993).…”

“…Bentley and Sparks, 2003). The investigation reviews 10 years of derecho data in order to detail the tendency for these convective events to form in succession.…”

“…In a larger climatological study, Bentley and Sparks (2003) established the tendency for derechos to 'train' or group over similar regions. They found a high propensity for summer, northern-tier US derechos (a corridor reminiscent of Johns (1982) NWF scenario) and northeast-moving Great Plains derechos to occur in groups.…”

Environment and Early Evolution of the 8 May 2009 Derecho-Producing Convective System

“…Derechos have been observed during all months of the year and in most locales east of the Rocky Mountains but occur most frequently in late spring and summer across the midwestern United States (Johns and Hirt 1987;Bentley and Sparks 2003;Coniglio and Stensrud 2004). The 8 May 2009 system developed in a way that is common for MCSs: convective initiation occurs along the eastern slopes of the Rocky Mountains and storms move eastward and consolidate in regions of lower-tropospheric warm advection, convergence, and conditional instability, all of which are enhanced by a nocturnal low-level jet (LLJ) (Blackadar 1957;Bonner 1968;McNider and Pielke 1981;Cotton et al 1989;Laing and Fritsch 2000;Tuttle and Davis 2006).…”

A 10‐year spatial climatology of squall line storms across Oklahoma

“…Subsequent definitions of other linear convective storms have been applied to more extreme events such as derechos (Johns and Hirt, 1987) and bow echoes (Fujita, 1978). Using set derecho definitions, studies such as Bentley and Mote (1998), Bentley and Sparks (2003), and Coniglio and Stensrud (2004) have quantified the frequencies of such storms across the United States and identified noticeable shifts in high-frequency regions stretching from the Great Lakes region through the Southern Plains during the warm season (May to August) to the lower Mississippi Valley during the cool season (September to April). Burke and Schultz (2004) focussed on the climatologies of bow echoes during the typically lower-frequency cool season and found similar spatial patterns as revealed in several derecho studies.…”