The Lewiston Tornado Event

July 8th, 1999

The Set-Up Before the Storms:
A dying MCS (mesoscale convective system) kept much of the area under some sort of cloud cover through the morning and early afternoon hours. Temperatures were initially cool as a result. The atmosphere was already unstable, with good shear and other dynamic components. A "kicker" was all that was needed to get things started. A low pressure system was approaching from the northern plains, with a warm front pushing north into central Minnesota and northern Wisconsin. Dewpoints in the low to mid 70s were pooling out ahead of the cold front associated with the low. By mid-afternoon, a break in the cloud cover occured over southeast Minnesota, northeast Iowa, and western Wisconsin. This basically left the La Crosse Weather Service's forecast area under bright sunshine, and under the gun. Temperatures rapidly warmed and dewpoints climbed. CAPE's (convectively available potential energy) climbed into the 4000 J/kg range, and with storm relative helicities from 0-3km averaging around 300, the atmosphere was ripe for supercell development. When convection finally initiated by late afternoon, it was explosive, with cells developing very rapidly.

  • Surface chart from 3 pm.
  • Animated visible satelite imagery. The loop starts at 415 pm and runs to 745 pm. (note: this will take a bit to load, and due to resolution limitations, the county/state backgrounds are fragmented).
  • Animated radar reflectivity images. The loop starts from 6 pm and runs to 750 pm. (note: this will take a bit to load)
  • A radar image (storm relative velocity) of the Lewiston tornado being sampled.


Lewiston Minnesota tornado - F2
Todd Shea, Warning Coordination Meteorologist
Picture of the tornado track.

The tornado touched down on the northwest side of Lewiston, damaged nearby homes and a farm implement dealer before tracking further into town. The tornado intensified right in the middle of town and tracked along main street to the southeast corner of town. Numerous homes along main street suffered extensive damage with broken windows, damaged roofs and downed trees. One home had the entire roof taken off while at least 4 cars were demolished from debris landing on them.

The tornado damaged a few homes in the southeast corner of Lewiston before entering corn fields for approx. 2 miles further. One farm had every building, except the house, demolished. The track of the tornado was clearly visible in the corn fields from the air. The tornado lifted just before the intersection of county roads 23 and 25.

There were 2 minor injuries reported, with 4 homes completely destroyed and 26 others sustaining damage. Length of the tornado track was 3 1/2 miles and peak width was approx. 100 yards. Peak damage indicates an F2 tornado, but most of the damage was F0/F1 variety. Interviews confirmed the tornado touched down at 720 pm, but people heard outdoor warning sirens between 700 and 705 pm. The National Weather Service issued a tornado warning at 700 pm.

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Along Main St., roof off in places, major house damage.

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More home damage.

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Debris, broken windows, roof damage.

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Winds pushed car through and crumpled garage door.

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Back of garage with neighbors roof blown into garage.

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Damaged van which had been moved by the wind.

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Warehouse which lost 1/2 its roof.

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Large pine down, home damage.

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Worst damage in Lewiston. F2 damage.

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Same house, close-up.

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Debris, more roof damage.

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Large tree upside down...believe the trunk was about 2 blocks down the street.

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Truck damaged by debris.

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Major roof damage.

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East end of town.

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Broken windows...the trunk from the missing tree?

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House which lost part of its roof.

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More home damage.

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More roof damage.

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Part of wall missing.

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Todd Shea, WCM, conducting the aerial part of the damage survey.

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Main St. in the left-center of picture.

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Whitish line on left-center is tornado path. Notice the house was spared, but not the barn.

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Close up of the farm from previous picture.

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East end of town.

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Along Main St.

*thanks to television station KSTP Channel 5 from Minneapolis/St. Paul for taking us up in their helicopter and getting the aerial pictures.

Mondovi Wisconsin tornado - F0/F1
Todd Shea, Warning Coordination Meteorologist
Picture of the tornado track.

A broad area of circulation produced occasional small tornado touch- downs across northeast Buffalo county, from approx. 8 miles southwest of Mondovi, through the city of Mondovi, to 4 miles northeast of Mondovi. Numerous trees were sheared off along the path with occasional homes or barns sustaining minor damage.

Two homes in Mondovi had roofs removed or garages damaged. Interviews indicated the tornado hit Mondovi itself around 632 pm on Thursday. Lighter damage, with mainly trees blown down, occurred in a path approx. 250 yards at times but the structural damage to homes was very narrow, 30 yards at most. This type of damage appears to be F1 in intensity and there were 3 reported injuries. A severe thunderstorm warning was issued, mentioning the possibility of tornadoes, at 622 pm.

A tornado watch was issued by the storm predicition center of the National Weather Service for this entire area at 550 pm on Thursday afternoon.

Medary/Barre Mills/Shelby/St Joseph Wisconsin - Straight-line winds/downbursts
Michael A. Welvaert, Meteorologist

Strong to severe thunderstorms moved across the Coulee region of southwest Wisconsin during the evening hours of July 8, 1999. While over southeast Minnesota, the storms produced a wide variety of severe weather, including at least 2 tornadoes, in Lewiston, MN, and Mondovi, WI.

A Severe Thunderstorm Warning was issued for La Crosse county at 736 PM CDT, highlighting the threat for Holmen at 750 PM, and the La Crosse area around 800 PM. Reports of strong winds and some hail were received from these storms, including dime to nickel size hail in Onalaska around 815 PM. The heart of the storm passed very near the National Weather Service office on the ridge east of La Crosse between 820 PM and 835 PM. A strong mesocyclone and apparent wall cloud were observed passing just to the north of the office. A wind gust to 58 mph from the south was measured at the office at 826 PM as the mesocyclone arrived, with a gust to 72 mph out of the north at 828 PM as it passed. This mesocycloe remained strong and very evident on radar imagery all the way through La Crosse county, southern Monroe county, and into northern Vernon county before weakening. A Tornado Warning was issued for La Crosse county at 828 PM CDT, based on radar and observed characteristics. Numerous reports of tree and home damage were received all under this mesocyclone during it's life cycle from Barre Mills, across the Medary and Shelby areas, and on toward St Joseph and Middle Ridge.

A storm damage survey was conducted on the morning of July 9, 1999, by Senior Meteorologists Michael Welvaert and Corey King.

The survey began near the Shelby/Medary town line, along Three Town Road, east of the weather office, and just north of county road F. Numerous trees were down in scattered fashion, with the primary fall direction toward the east. Further north on Three Town Road, we encountered a Farm where the roof was blown off of the barn, and the north and east walls were blown out. Trees were down all over the farm yard, and part of the barn roof was lying south of the structure on the driveway. The vast majority of the debris here was all blown toward the southeast, but a few pieces of the roofing material were scattered to the south and south-southwest. Further down the road, there was a bank of trees that were blown down across the roadway, partially blocking it. The hillside trees below this spot were also blown down, from a west to east direction. At the end of the road, there was a farm. There, a tree was blown down from west to east, but the occupants of the farmstead told of their swing set moving east to west. Comparing radar imagery to a map of the area, suggest that the differing directions of wind were due to the close proximity to the mesocyclone and its associated wind shifts, as demonstrated previously with wind measurements at the La Crosse Weather office. It is possible that small shear zones existed within the mesocyclone during this time frame, which may have enhanced some of the damage, but this would have primarily been on the ridgetops.

We then traveled further to the east, and found extensive damage near the intersection of highways FO and OA, near the entrance to Hagenbarth Coulee. Three homes received serious damage as trees fell onto them, and at least one automobile was crushed by fallen limbs. Trees were observed to be snapped off mid-way up the trunk, but again all debris was strewn mainly from west to east. Additional damage was noted further north along highway OA, in the Garber's Coulee area. A barn had part of its roof blown off, some wagons were turned over, and extensive tree damage was noted to the west of the roadway. Many of these trees were snapped off mid-trunk, and some showed twisting. Again, the vast majority of the damage was strewn from west to east. The scattered nature of these damage locations, and the orientation of the damage again suggested wind damage associated with the mesocyclone, and its attendant microbursts.

We then traveled a little further north, and then went west on Drectrah Coulee Road. This road runs to the southwest for a few miles, and then ends. Severe damage was noted during about the last mile of this roadway. One home was destroyed, and at least 2 others had parts of their roofs blown off. There was severe tree damage, with trees blocking the roadway. The road had been cleared enough by chain saw to allow one lane of passage. The majority of the damage was done on the southeast side of the roadway, where the terrain rose. Most of the debris was thrown from southwest to northeast, along the direction of the Coulee. These things suggest that the terrain acted to focus this particular microburst into a localized area, and hence the large quantity of damage.

We then traveled north back along highway OA, to highway O. We traveled west on highway O, and then west on highway B. From highway B, we proceeded south along Smith Valley Road. No damage was observed along this route. However, as we reached the end of Smith Valley Road, we observed tremendous damage to the Bluebird Campground. We spoke with Manager Dar Ray, and she estimates that 85% of the campground is damaged. Indeed, over 100 large trees were down, many snapped off at mid-trunk. Campers and automobiles were crushed or otherwise damaged. Damage patterns in the camp highly suggest a microburst, further focused by the surrounding topography, with the camp sitting down in a Coulee, surrounded by steep hills. A microburst along the slope to the west looks to have focused the wind right down the Coulee into the campground.

Also of note: A small creek runs parallel to Smith Valley Road. The grasses and shrubs along the creek leave evidence of a minor flood, with water well out of the banks. Many driveways exist over this creek to homes on the other side, and all have varying degrees of bridges. Most have low water crossing type bridges, and these were inundated. One home had a well-constructed wooden span over the creek, and it was noted to have a large tree trunk near it and across the driveway. Vegetation marks indicate that it was carried there by the flowing water.

An independent damage survey was also conducted by the La Crosse County Emergency Manager, Al Spalding He surveyed a similar area, and also toured damage further to the east, along State Highway 33. Many trees were downed, according to Mr. Spalding, near and just southeast of St. Joseph. A few trees and a barn were blown down at the corner of Route 33 and Bina Road, just east of St. Joseph. We met at the La Crosse National Weather Service office later that morning, and the findings of both surveys were similar.

We were in concurrence that the storm damage was the result of strong winds associated with the mesocyclone. Strong inflow from the south and southeast on the leading edge of the mesocyclone reached estimated speeds of 50 to 70 mph. The Rear Flank Downdraft behind the storm resulted in estimated wind speeds in the 80 to 100 mph range. The survey showed that these winds, when focused by the terrain features, likely exceeded 120 mph in a few locations. In addition, there was strong evidence of cyclic microbursts within the wind flow around the mesocyclone.

Although there were a few comments by citizens that they saw funnel clouds, and despite the favorable position in the storm for such a phenomenon, it is the opinion of the National Weather Service, and the La Crosse County Emergency manager, that the damage was NOT the result of any tornadic activity.

An additional survey was performed by Science and Operations Officer, Dan Baumgardt, in and around the Viroqua, WI area. Minor structural damage along with downed trees were found in a few locations, but there was no evidence of tornadoes.

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2x4's driven through side of garage.

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A view from inside the garage.

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Barn destroyed by the winds.

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Another view of the barn damage.


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