A devastating derecho developed during the afternoon and evening of July 19th
2006. It caused tremendous damage and unprecedented power outages across the
western half of Illinois as well as east-central Missouri. Over 600,000 people went
without power for as much as a week after the storm. The St. Louis area was
especially hard hit, with over a half million people left without power in that area
alone. During the event, about 35 people sustained injuries, with no deaths. The
majority of the injuries occurred at Busch stadium, where 30 people were injured as
the storm hit during a Cardinals game. During the several days of power outages,
heat and humidity levels sky-rocketed, with heat indices reaching between 110 and
115 degrees F.
The major power company in Illinois and Missouri, Ameren Corporation, called the
storm the most damaging in the company’s 100 year history. One reason for the
tremendous number of power outages, especially around St. Louis, may be
attributed to the winds coming from an unusual direction. Typical winds during
damaging wind events in that area usually have more of a westerly component.
These damaging winds were northeast, which may have hit trees from a direction
where they had weaker resistance to breaking or uprooting.
The forecast for this storm system was a difficult one, both nationally and at the
local WFO level. Early indications were that any storms that developed in the highly
unstable atmosphere over eastern Iowa would not maintain intensity much farther
south than northern Illinois. Central and southern Illinois areas were more stable
comparatively, as seen through examination of SPC meso-analysis graphics.
However, the storm progressed from eastern Iowa, southeast into northern Illinois,
then straight south through central Illinois. After causing widespread damage in
central Illinois, the storm eventually moved southwest toward St. Louis MO. Corfidi
vectors gave an indication that this type of path was possible, but stability
parameters indicated the storms most likely would not survive that long in central
Illinois.
This study will focus on the meteorological conditions that occurred that day as well
as the radar data from Lincoln IL and St. Louis MO. Attention will also be given to
meso-scale models, including the NCAR 4-km WRF run by Dr. Morris Weisman. It
is hoped that the meteorological data will reveal some indications in the precursor
environment that could have helped predict the storms eventual life cycle and storm
path.
|
