Figure 1: Mapping of the July 5, 2004 downburst event over parts of southwest Illinois. Downburst winds within the shaded light blue represent the greatest degree of wind damage with this event. Based on damage to structures and trees wind speeds were estimated between 65 and 85 mph. Wind speed estimates north (above) the shaded blue region over extreme northern St. Clair, extreme southeast Madison and northern Clinton counties varied between 55 to 65 mph.
Figure 2: Tree damage near the west side of the O'Fallon, Illinois Police Department complex. Viewing south.
Figure 3: Additional tree damage over the southeast part of O'Fallon. Many of the large limbs and trees down occurred along the southern half of the city of O'Fallon and southward to Interstate 64.
Figure 4: One of several large trees uprooted 3 miles north of Mid America airport along and east of Illinois Route 4. This area of tree damage was associated with the downburst crossing Interstate 64 and Illinois Route 4.
Figure 5: Additional tree damage 3 miles north of Mid America Airport along Illinois Route 4.
Figure 6: Damage to a machine shed on a farmstead 1 mile west of Lebanon, Illinois. Viewing north.
Figure 7: Damage to one of two homes over the southern part of the town of Summerfield, Illinois. The west side of the roof from this home is severely damaged. Viewing south. Several large trees were uprooted southwest from this location.
Figure 8: Damage to one of several homes due to fallen trees in the town of Trenton, Illinois. Many of the trees were originally 40 to 50 feet tall. Viewing northeast.
Figure 9: Additional tree damage near the north side of Trenton, Illinois (western Clinton County).
Figure 10: Corn partially flatten 3 miles south of Trenton along Illinois Route 160 in western Clinton County. Viewing east.
Figure 11: Low-level plan view reflectivity image from WFO St. Louis taken at 8:36 pm reveals the second bow echo moving east across St. Clair county in southwest Illinois.
Figure 12: Shows low-level base velocity image from KLSX radar at 836 PM CDT.
Figure 13: Low-level plan view reflectivity image from WFO St. Louis taken at 9:36 pm reveals the third bow echo moving east across St. Clair county in southwest Illinois.
Figure 14: Shows low-level base velocity image from KLSX radar. A very small group of very bright red pixels just southeast of O'Fallon, Illinois represents an area of 93 kts detected by the Doppler radar (outbound velocities). At 942 pm CDT, the wind instrument at Scott AFB recorded a gust of 92 mph.

NWS
St. Louis, Missouri

Downburst Wind Event
over parts of Southwest Illinois
July 5th, 2004

A NWS survey team found considerable downburst wind damage over portions of southwest Illinois.   Below there is a map of the July 5th, 2004 downburst event.  Downburst winds within the shaded light blue represent the greatest degree of wind damage with this event.  Based on damage to structures and trees wind speeds were estimated between 65 and 85 mph.  Wind speed estimates north the shaded blue region over extreme northern St. Clair, extreme southeast Madison and northern Clinton counties varied between 55 to 65 mph.  This region experienced three episodes of severe convective lines and bow echoes on July 5, 2004.  Weather spotters observed two funnel clouds over extreme northwest Clinton County along the leading edge of the second convective line (bow echo) between 8:30 and 8:45 pm CDT.  The funnels descending about half way to the ground but never touched down.  The greatest degree of wind damage occurred with the third convective line segment between 9:30 and 10:15 pm CDT.  Wind speed information at Highland, Illinois was taken from the weather station at the Highland Fire Department.  We wish to extend our thanks to the O'Fallon, Illinois Police Department, Trenton Illinois Police Department, Highland Fire Department, and severe storm spotters for their assistance during the damage assessment.  The images below are a small sample of the damage done by downburst winds produced by the second and third convective systems during the evening of July 5th, 2004.

Damage Map of Downburst Winds July 5th, 2004
Tree damage in O'Fallon, IL
More tree damage in O'Fallon, IL

Tree damage south of Lebanon

Tree damage south of Lebanon

Machine shed damage near Lebanon

Homes damaged near Summerfield

Home damage in Trenton

Tree damage in Trenton

Corn Field damage near Trenton

Radar reflectivity image at 836 PM CDT

Radar base velocity image at 836 PM CDT

Radar reflectivity image at 936 PM CDT

Radar base velocity image at 936 PM CDT

 

 


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