Figure 1: Detailed map of the Marissa Illinois tornado track and nearby microburst damage on August 19th, 2004.
Figure 2: Damage to two machine sheds near the southwest corner of Lenzburg East Road and Illinois Route 4 in far southeast St. Clair County. Windows and siding from a nearby farm home (immediately left of the picture) were damaged. Witnesses at this farmstead and an adjacent farmstead observed the tornado and described it having a milky white appearance. Viewing southwest.
Figure 3: Debris from the machine sheds was scattered north of Lenzburg East Road and west of Illinois Route 4. Viewing north-northwest.
Figure 4: In addition to the scattered debris, a few large trees were snapped near the base of the trunk. Viewing east-northeast.
Figure 5: Scattered tree damage north of Lenzburg East Road and immediately west of Illinois Route 4. Viewing northeast.
Figure 6: Approximately 3/4 mile northeast of the intersection of Lenzburg East Road and Route 4, several trees were snapped halfway up in a wooded area. Viewing northeast.
Figure 7: A microburst partially or completely flattened corn along and south of the tornado track east of Route 4 and along and north of Erb Road.
Figure 8: Low-level plan-view reflectivity image from WFO St. Louis at 4:42 PM CDT showing the discrete mini-supercell which spawned the weak tornado and caused wind damage south of the tornado track.
Figure 9: Shows the low-level storm-relative velocity image of a weak mesovortex just prior to tornado touchdown. The mesovortex is located near the northwest side of the discrete storm.
Figure 10: Low-level plan-view reflectivity image taken at 4:52 PM CDT from WFO St. Louis. The discrete mini-supercell moved into far southwest Washington County Illinois.
Figure 11: Low-level plan-view of storm-relative velocity image showing a second mesovortex with this storm. This mesovortex was responsible for producing wind damage.

NWS
St. Louis, Missouri


Marissa, IL Tornado & Damaging Wind Event
August 19th, 2004

During the late afternoon of August 19th, 2004 discrete convective storms developed over northern Randolph County Illinois and moved east-northeast into far southeast St. Clair County. One of the stronger storms spawned a weak (F0) tornado 4 miles north-northeast of Marissa and caused minor structural and tree damage beginning 1 mile southwest of the intersection of Lenzburg East Road and Illinois Route 4. Two microbursts were identified during the assessment, one adjacent and southeast of the tornado track and a second approximately 1 mile south of the tornado track. Tree and corn damage were noted with each of the microbursts. The overall width of the tornadic damage track was approximately 40 yards while the overall damage length was 2 miles.
Damage Map of Marissa, IL Tornado Track August 19th, 2004
Machine shed damage
Machine shed damage

Tree damage

Tree damage

More tree damage

Corn crop damage

Reflectivity image at 442 PM CDT

Storm relative velocity image at 442 PM CDT

Reflectivity image at 452 PM CDT

Storm relative velocity radar picture from 452 PM CDT

 


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