Reviewer's Abstract
2002 National Weather Association Annual Meeting
October 2002, Dallas - Fort Worth Texas
BRIEF
OVERVIEW OF TWO TORNADIC QUASI-LINEAR CONVECTIVE SYSTEM (QLCS) EVENTS OVER THE
MID-MISSISSIPPI VALLEY REGION DURING THE SPRING 2002 SEVERE STORM SEASON
Ron W. Przybylinski
and
Gary K. Schmocker
NOAA/Weather Forecast Office
12 Research Park Drive
St. Charles Missouri 63304
The Spring 2002 convective
season across the Mid-Mississippi Valley Region was extremely active with three tornadic
supercell events and five tornadic bowing convective line events. Most of the
tornadic cases occurred during the period of mid-April through mid-May 2002 with some of
the events occurring every five days. Over twenty tornadoes were documented in the
WFO St. Louis County Warning Area (CWA) during this period with many of them causing F1
damage. In some areas, residents of south-central Illinois experienced damage twice
within a two week period. Ground-based damage surveys were conducted for all of the
tornadic events. This presentation will compare the environmental and storm
evolution of two of the five convective line tornadic events. The first tornadic
event occurred during the early morning of May 9, 2002 as a non-supercell tornado caused
extensive damage in a one mile path across the southeast part of the community of
Centralia Illinois, about 145 km east of the KLSX (St. Louis) Doppler radar. Two
fatalities occurred in a mobile home park. A small bow echo embedded within a
larger convective line moved east-northeast across Clinton and Fayette counties northwest
of Centralia and caused scattered wind damage. Timely severe thunderstorm warnings were
issued for this storm. However, a larger broad bowing segment responsible for the
non-supercell tornado evolved south of the smaller bow and just ten minutes prior to the
time of tornado occurrence. Preliminary observations of the storm-relative velocity
data showed little signs of any vortex development in the Centralia Illinois area.
The second bow echo tornadic event occurred during the early evening of May
12, 2002 over southeast Missouri or 140 km south of KLSX. An isolated storm formed
30 km downwind of a developing bowing segment and laid a southwest-northeast low-level
boundary. Small convective cells formed upwind of the larger isolated storm and
helped in identifying the location of this low-level boundary. A circulation
formed just north of the apex of a bowing structure and gradually interacted with the
northward moving low-level boundary. The convective-scale vortex intensified and
deepened just after the interaction with the low-level boundary. A tornado
occurred approximately five minutes after the low-level boundary intersected with the bow
echo and caused F0-F1 damage from 5 km west of Desloge through the town of Desloge
Missouri (10 km northwest of Farmington MO). This type of storm evolution has been
documented in previous MCS events over the Mid-Mississippi Valley region and appears to
fit the Type 2 MCS Category documented by Przybylinski et al. (2002). The storm
reflectivity - Doppler velocity structures of this event will be shown and compared
to the Centralia Illinois event.
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