NOAA's National Weather Service Weather Forecast Office

PRELIMINARY DAMAGE SURVEY FOR WASHINGTON...ST. FRANCOIS...STE GENEVIEVE COUNTIES IN MISSOURI AND
SOUTHWEST RANDOPLH COUNTY IN ILLINOIS

National Weather Service personnel at St. Louis completed a survey of the damage over parts of Washington...St. Francois... Ste Genevieve counties in southeast Missouri and Randolph county in southwest Illinois.   Preliminary results show that three tornadoes and multiple downburst wind swaths occurred over this area.

The first of three tornadoes briefly touched down about 6 miles southeast of Potosi Missouri in eastern Washington county.  Several trees were damaged by the tornado.  The tornado occurred at approximately 610 PM CDT.  The damage path was about 100 yards long and 30 yards wide.  Damage was rated F0 on the Fujita scale.   The second tornado initially touched down near the just north of the community of Frankclay on Highway M in western Ste Francois county at approximately 618 PM CDT.  A number of trees and large tree limbs were stripped or damaged by the tornado. The tornado path over this area was relatively narrow approximately 30 yards and damage was rated F0.  The tornado moved eastward across the community of Desloge mainly causing tree damage along Chestnut stree west of Highway 8.  The tornado moved east of Highway 8 along and south of Chestnut street causing scattered tree damage and destroying one utility pole near Elm street and the Middle School.  A few homes and the middle school sustained mainly minor roof damage, although one large tree fell onto a house trailer.  The tornado path was approximately 40 yards and was rated F0. 

The tornado turned northeast across Chestnut street then moved over an open field west of State street.  One half of the roof of a large machine shed was thrown east over 200 yards. Several downed trees showed the classic convergent pattern noted with tornadic damage immediately south of the machine shed and a large home.  The damage pattern suggested a touchdown of a second funnel just northeast of the machine shed.   Both funnels appeared to merge just west of State Street. Several large trees were significantly damaged 80 yards east of the large home and machine shed.   Three homes on the west side of State street sustained minor roof and siding damage. One two by four piece of wood was driven into the north side of one home.  A small utility shed and garage behind one of the home was destroyed.  Pieces of mangled sheet metal from the large machine shed landed in the front yard of two of the three homes. The damage was approximately 100 yards wide over this area.

The tornado then hit a vacant two story building just east of State street completely uplifting the roof and causing considerable damage to two sides of the building.  The tornadic damage path was less than 50 yards but the damage was rated F1 at this location.   The tornado skipped across Highway 67 and hit a another large sheet metal building on the east side of the highway. The north side of the roof of a second large building was uplifted and displaced several tens of yards to the east.  Over 100 yards east of this building additionaly tree damage was observed.  The width of the damage path over this area was less than 40 yards and the damage was rated F0.

The total length of the damage path of this tornado was 7.0 miles. 

Damaging downburst winds were documented across parts of western and central Ste Genevieve county mainly along and south of County Road C and north of Highway 32.

Map of tornadic damage paths over eastern Washington and St. Francois counties.

Damaging downburst winds were documented over western and central sections
of Ste Genevieve county. 

A second brief tornado touchdown occurred in a subdivision over the south side of Chester Illiniois (south of the City Park)in southwest Randolph county.  One home sustained roof damage while a second home experienced minor stripping damage.  Several pines were snapped at the base while a number of large white oak trees were either torn off 15 feet from the base of the tree or twisted near the base of the tree.  A convergent damage pattern was observed over this area.  The length of the tornadic damage track over this area was roughly 100 yards long and 30 yards wide.  The damage was rated F0. Minor tree damage was observed just south of the tornado track along and west Highway 3.

Map of tornadic damage path over southern part of Chester Illinois.  A weak microburst was observed to the southeast of the tornado track.

The tornadoes which caused damage over parts of eastern Washington, and St. Francois counties in Missouri and far southwest Randloph county Illinois are referred to as 'non-supercell tornadoes'   which formed just north of the apex of a bow echo.  A low-level outflow boundary from an earlier storm intersected the bow echo and likely enhanced the potential for tornadic activity.  The tornado over St. Francois county had a longer lifespan compared to the tornado over Shiloh Illinois on April 27, 2002. 


Fujita Scale
F0 -  40 - 72 mph
F1 -  73 - 112 mph
F2 -  113 - 157 mph
F3 -  158 - 206 mph
F4 -  207 - 260 mph
F5 -  261 - 318 mph

S. Truett
R. Przybylinski
National Weather Service St. Louis

Photos (thumbnails) of the tornadic damage over the southern part of Chester Illinois - early evening  May 12 2002.

Reflectivity image (0.5° slice) (top) at 607 PM CDT from KLSX (St. Louis) radar shows a developing bow echo west of the Desloge - Park Hills area.  An outflow boundary from a strong isolated rstorm downstream of the bow  intersects the southern part of the bow echo at this time. The Storm-relative velocity (below) image taken at this same time shows a moderate intensity mesocyclone near the apex of the bow echo.   A weak - short-lived tornado caused damage to several large trees (F0 intensity) near the town of Hopewell in eastern Washington County.

Reflectivity image (0.5° slice) (top) at 622 PM CDT from KLSX shows a mature bow echo moving east across St. Francois county.  The bow echo accelerates eastward towards the isolated storm.  The northeastward moving outflow boundary intercepts Circulation 1  near the apex of the bow and likely caused this vortex to intensify.  Storm-relative velocity image (below) shows strong rotation over Desloge (strong mesocyclone - Vr 45 kts ) just north of the bow apex - outflow boundary intersection.  Circulation 1 spawned a tornado and caused F0-F1 damage from the town of Frankclay (6.5 miles west to 0.5 miles east of Desloge.

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