F3 Tornado — Dane, Wisconsin

2005-08-18 · near Fitchburg, Dane, Wisconsin

Event narrative

A strong and destructive tornado spun up at 1715CST about 2.8 miles southeast of the geographic center of Fitchburg (or 2.0 miles north of center of Oregon), about 400 yards southwest of the intersection of CTH MM and Schnieder Rd. It continued east-southeast to the southern edge of Lake Kegonsa and tore through residential neighborhoods about 1/3 to 1/2 mile north of CTH B (Civil Towns of Dunn and Pleasant Springs, and far-northern Stoughton). It moved over the crossing of CTH A with Interstate 90/39, and stayed close to CTH A to its exit point at 1905CST where CTH A crosses into Jefferson County, about 2.8 miles south-southwest of Rockdale. One person was crushed to death in their basement from fireplace and chimney bricks that crashed through the floor. Twenty-three (23) other people were directly injured. In addition, Emergency Management officials received reports of 2 other indirectly-related deaths associated with this strong tornado. In these two cases, the people were already very ill or suffering from a life-ending disease. Injuries they received during the tornado contributed (secondary) to their death, but were not the primary cause of death, based on medical examiner reports. Consequently, these additional two deaths do not appear in the official death tally in the header strip of this event. Numerous homes, businesses, farm buildings, vehicles, power-lines, trees, and other personal effects were either damaged or destroyed along its path that grew to a maximum width of about 600 yards north of Stoughton. As for residential structures, 220 sustained minor damage, 84 had major damage, and 69 were destroyed. As for business structures, 6 sustained minor damage, 1 had major damage, and 1 was destroyed. As for agricultural structures, 5 sustained minor damage, 5 had major damage, and 40 were destroyed. Total estimated damage amounts (directly-related) for private and public sectors combined was $35.06 M, broken down to $34.31 M in property damage and $750 K in crop losses, for the tornado segment in Dane County. This tornado was probably the 3rd most costly tornado in Wisconsin's recorded history (1996 Oakfield tornado and 1984 Barneveld tornadoes were more costly). The $34.31 M in property damage was broken down to private losses (total of 32.29 M) and public losses (total of $2.02 M), per Emergency Manager reports and NWS estimates. The private losses included a total of $25.45 M for residential structures, $1.29 M for businesses, $4.25 M for agricultural structures, $1.00 M for damage to vehicles, boats, and other personal effects, $200 K to agricultural machinery and tools, and $96 K in public road system damage. The public losses making up part of the $34.31 M consisted of $2.02 M in damage to public utility systems. The $750 K in damage attributed to crop losses occurred on an estimated 1,550 acres of land. Additional monetary costs incurred in the public sector (totaling $1.84 M) which are considered indirectly-related damage expenses, and not included in the "direct" totals listed in the header-strip of this event, include: $1.38 M in debris clearance, $308 K in protective measures, and miscellaneous damage/expenses of $144 K. Therefore, the grand total of direct and indirect damage amounts and expenses attributed to this tornado segment in Dane county totaled about $36.89 M.Just south of the tornado, extending out another mile or so, tree and power-line damage resulted from rear-flank downdraft damage - in some cases south to STH 51. This damage is separate from tornado damage, and isn't included in the numbers in previous sentences. Debris from this tornado was lofted by the parent's updraft and carried downstream to scattered locations in the counties of Jefferson, Waukesha, Milwaukee, Walworth, Racine, and Kenosha. This tornado was extensively photographed and video-taped by storm spotters (amateur radio operators, etc.), storm chasers, and private citizens. On occasions, this tornado displayed multiple-vortex characteristics. Due to partial back-building (to the west-southwest) of the supercell's updraft tower, this tornado moved slowly, and was described by some eyewitnesses and spotters as being nearly stationary at times north of Stoughton. The overall slow movement (supercell moved at 12-17 knots, or 10-15 mph), coupled with structures that were not thoroughly reinforced (based on NWS damage survey), allowed the tornado's cyclonic winds to more severely damage buildings in its path. Consequently, although some of the worst damage resembled what would be left by a F4 tornado for well-built homes, this tornado was rated at the top of the F3 category with estimated winds near 174 knots (200 mph). The F3 category has estimated wind speeds of 137-179 knots (158-206 mph). A sampling of newspaper headlines and personal quotes included: "The Sky Just Exploded," "Hard to Believe There Weren't More Deaths," "New Technology Lowers Tornado Deaths," "Counting Losses, Blessings," "It Was Probably The Most Intense Storm In The Country This Year," "It's a Mess Out Here," and "I've Never Experienced Anything Like This." The tornado cut electrical power for 1700 customers in the Stoughton area. The estimated average path length was about 175 yards.

Wider weather episode

The largest single-day tornado outbreak in Wisconsin recorded history for south-central and southeast Wisconsin occurred on August 18, 2005. Sixteen tornadoes were documented on this day in south-central and southeast Wisconsin, a new single-day record. A line of supercells developed and pushed across south-central Wisconsin during the afternoon hours, and then pushed east across southeast Wisconsin during the evening hours. Most of the tornadoes were associated with two supercells. One main supercell tracked across Sauk County and then into Columbia, producing one F0 and one F2 tornado. The F2 tornado crossed into Columbia County. Another main supercell produced an F3 tornado that devastated the area north of city of Stoughton (Dane Co.), and a weaker F1 tornado just south of the city of Rockdale (Dane Co.). This supercell then tracked into southwestern Jefferson County a short time later, producing two F0 tornadoes and four F1 tornadoes. The sixteen (16) tornadoes contributed largely to both the new state record of 27 tornadoes on a single day, and 62 tornadoes for a calendar year. In additiion, there were scattered reports of funnel clouds, damaging straight-line, downburst winds, and large hail across south-central and southeast Wisconsin. The total direct damage estimate for the afternoon and evening tornado and severe weather outbreak in south-central and southeast Wisconsin on August 18th was about $36.6 M ($35.7 property and $948 K crop). Additional indirect costs totaled almost $1.9 M, resulting in a total direct and direct cost of about $38.5 M. Synoptically, a surface low pressure system was located over extreme southeast Minnesota early in the afternoon. A warm front extended east southeast from the low with dew points pooling in the lower 70s along it. The surface low moved east into east central Wisconsin by 2100CST that evening. Favorable wind shear associated with the warm front, combined with the strong instability supplied by the heat and humidity, helped to produce numerous tornadic supercells.

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Source: NOAA Storm Events Database, event_id 5475742. Narrative written by the NWS forecast office that issued the report.