Tornadoes · United States · Wisconsin · 2015
EF1 tornado, Lake Geneva to Lyons Arpt, Wisconsin, August 18, 2015
From Lake Geneva to Lyons Arpt, this EF1 tornado ran 4.9 miles across Walworth County on August 18, 2015, touching down at 8:56 PM CDT and reaching 75 yards wide. It killed nobody, and did $100,000 of property damage.
The rating scale
Tracks are drawn in the color of the rating. The Enhanced Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.
EF065 to 85 mph
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
EF186 to 110 mphthis tornado
Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.
EF2111 to 135 mph
Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.
EF3136 to 165 mph
Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.
EF4166 to 200 mph
Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.
EF5over 200 mph
Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.
Unrated
The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.
The record
- Rating
- EF1
- Date
- August 18, 2015
- Touchdown
- 8:56 PM CDT (01:56 UTC)
- Lifted
- 9:06 PM CDT (02:06 UTC)
- On the ground
- 10 minutes
- Path length
- 4.9 miles (7.9 km)
- Path width
- 75 yards (69 m)
- Deaths
- 0
- Injuries
- 0
- Property damage
- $100,000
- County
- Walworth County
- Touchdown point
- 42.588, -88.431
- Lift-off point
- 42.655, -88.397
- Record number
- 1508181956-01
The damage survey
49 damage points were recorded along this path by NWS MKX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 110 mph.
- signs down opposite direction
- just before Arouca. looking away from aurora over a valley.
- getting to top of ef1 scale damage. buildings on top of hill
- not much damage to barn across street.
Survey points are preliminary and are the raw material the published rating was built from. Source: NWS Damage Assessment Toolkit.
What the Weather Service recorded
A strong low pressure system moved across the Upper Mississippi River Valley and Great Lakes region. A large area of showers and thunderstorms moved across southern WI and produced 3 tornadoes in southeast WI.
An EF1 tornado caused a sporadic path of damage. The most severe damage was significant roof damage to 4 buildings that were warehouse buildings and metal building systems. One of those buildings sustained a collapsed wall. There was minor damage to a mobile home and a barn. A couple large retail signs were destroyed. There were many trees uprooted and snapped.
From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.
The warnings
No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.
The county was under a tornado watch, issued at 18:47 UTC and running to 03:00 UTC.
| Issued (UTC) | Expired | Product | Office |
|---|---|---|---|
| 18:47 UTC | 03:00 UTC | Tornado Watch | MKX |
| 02:04 UTC | 02:30 UTC | Severe Thunderstorm Warning | MKX |
Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.
The forecast that day
The Storm Prediction Center had this point in a General Thunderstorms Risk. The outlook in force was issued at 01:00 UTC.
SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.
The air that afternoon
The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.
Davenport, (KDVN), 00:00Z
1.9 hours before the tornado, 205 km from the path. August 19, 2015.
- Mixed-layer CAPE
- 5 J/kg
- Mixed-layer CIN
- -188 J/kg
- Surface CAPE
- 344 J/kg
- Mixed-layer LCL
- 887 m above ground
- 0-6 km bulk shear
- 43 kt
- 0-1 km bulk shear
- 16 kt
- 0-1 km storm-relative helicity
- 91 m²/s²
- 0-3 km storm-relative helicity
- 156 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.1
- 0-3 km lapse rate
- 4.9 K/km
Davenport, (KDVN), 12:00Z
10.1 hours after it, 205 km from the path. August 19, 2015.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- -88233 J/kg
- Surface CAPE
- 4 J/kg
- Mixed-layer LCL
- 1055 m above ground
- 0-6 km bulk shear
- 39 kt
- 0-1 km bulk shear
- 24 kt
- 0-1 km storm-relative helicity
- 43 m²/s²
- 0-3 km storm-relative helicity
- 91 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
- 0-3 km lapse rate
- 2.7 K/km
The surface observations
Burlington (BUU), 12 km from the path, in the two hours either side.
| Time (UTC) | Temp (°F) | Dew point (°F) | Wind | Gust (kt) | Pressure (mb) | Weather |
|---|---|---|---|---|---|---|
| 00:15 UTC | 72.14 | 65.3 | 120° 6 kt | 1006.1 | ||
| 00:35 UTC | 71.78 | 66 | 120° 6 kt | 1005.8 | -RA | |
| 00:55 UTC | 70.88 | 67 | 110° 6 kt | 1005.1 | -RA | |
| 01:15 UTC | 70.16 | 67.82 | 110° 6 kt | 1005.1 | RA | |
| 01:35 UTC | 70 | 68.36 | 120° 7 kt | 1005.1 | RA | |
| 01:55 UTC | 67.28 | 65.66 | 260° 3 kt | 1004.4 | +RA | |
| 02:15 UTC | 68.18 | 67.28 | 150° 16 kt | 21 | 1004.1 | -RA |
| 02:35 UTC | 66.38 | 65 | 230° 5 kt | 14 | 1004.7 | +RA |
| 02:55 UTC | 66.2 | 65 | 240° 5 kt | 1005.1 | +RA | |
| 03:15 UTC | 65.66 | 64.76 | 240° 4 kt | 1005.1 | RA | |
| 03:35 UTC | 65.48 | 64.58 | 130° 4 kt | 1004.4 | -DZ | |
| 03:55 UTC | 65.66 | 65 | 180° 4 kt | 1004.7 |
From the Iowa Environmental Mesonet's archive of airport observations.
The radar
The Milwaukee radar (KMKX), 40 km away, was scanning. The volume nearest the touchdown began at 01:55 UTC.
Open the radar archive at this moment, over the track
Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.
What was reported nearby
Local storm reports within 60 km of the path, in the three hours either side.
| Time (UTC) | Report | Where | County | Remark |
|---|---|---|---|---|
| 01:58 UTC | TORNADO | 2 Nne Lake Geneva | Walworth, WI | EF1 TORNADO CAUSED SIGNIFICANT ROOF DAMAGE TO SEVERAL INDUSTRIAL BUILDINGS. WINDS ESTIMATED AT 110 MPH. TIME ESTIMATED FROM RADAR. |
| 02:15 UTC | TSTM WND DMG | Lake Geneva | Walworth, WI | METAL ROOFING AND DEBRI NEAR INTERSECTION OF HWY 120 AND HWY 12. DOORS RIPPED OFF AURORA HEALTHCARE BUILDING. TREES DOWN. |
| 02:15 UTC | TSTM WND DMG | Lake Geneva | Walworth, WI | METAL ROOFING AND DEBRIS NEAR INTERSECTION OF HWY 120 AND HWY 12. DOORS RIPPED OFF AURORA HEALTHCARE BUILDING. TREES DOWN. POSSIBLE TORNADO. |
| 02:31 UTC | TORNADO | 2 Sw Big Bend | Waukesha, WI | EF1 TORNADO CAUSED ROOF AND SIDING DAMAGE. WINDS ESTIMATED AROUND 100 MPH. TIME ESTIMATED FROM RADAR. |
| 02:37 UTC | TSTM WND DMG | 2 Sw Big Bend | Waukesha, WI | TREE DAMAGE REPORTED ALONG COUNTY ROAD L. POSSIBLE TORNADO. RELAYED VIA SOCIAL MEDIA. TIME ESTIMATED FROM RADAR. |
| 02:37 UTC | TSTM WND DMG | 3 Sw Big Bend | Waukesha, WI | DOWNED POWER LINES AND TREE DAMAGE. SMALL PATCH OF FLATTENED CORN STALKS. TIME ESTIMATED FROM RADAR. POSSIBLE TORNADO. |
| 02:44 UTC | TSTM WND DMG | 2 Ne Lake Geneva | Walworth, WI | TREES DOWN GREATER THAN 12 INCHES IN DIAMETER |
| 02:48 UTC | TSTM WND DMG | 2 Ssw Waukesha | Waukesha, WI | TREE DAMAGE REPORTED IN SOUTHWEST WAUKESHA. TIME ESTIMATED FROM RADAR. |
| 02:48 UTC | TORNADO | 2 Ssw Waukesha | Waukesha, WI | EF-0 TORNADO CONFIRMED IN WAUKESHA NEAR INTERSECTION OF GENESEE ROAD AND WISCONSIN 59. PRIMARILY TREE DAMAGE ALONG PATH. |
From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.
This ground now
The live radar over the trackEvery 2015 tornado in WisconsinEvery tornado in Wisconsin since 1950Warnings in force in Wisconsin nowThe forecast where you are
The other tornadoes of August 18, 2015
8 more were confirmed in the United States that day.
| Date | Time | Rating | Where | Path (mi) | Width (yd) | Deaths | Injuries | Damage |
|---|---|---|---|---|---|---|---|---|
| August 18 | 3:13 PM CDT | EF0 | Cedar, IA | 0.1 | 20 | |||
| August 18 | 4:32 PM CDT | EF0 | Livingston, IL | 0.0 | 25 | |||
| August 18 | 5:05 PM CDT | EF0 | Livingston, IL | 0.0 | 25 | |||
| August 18 | 6:09 PM CDT | EF0 | Tazewell, IL | 2.0 | 75 | $30,000 | ||
| August 18 | 7:55 PM CDT | EF0 | DuPage, IL | 3.2 | 75 | |||
| August 18 | 8:06 PM CDT | EF0 | DuPage, IL | 0.2 | 75 | $50,000 | ||
| August 18 | 9:25 PM CDT | EF1 | Waukesha, WI | 2.5 | 50 | $46,000 | ||
| August 18 | 9:50 PM CDT | EF0 | Waukesha, WI | 0.6 | 25 | $10,000 |
What this means
Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.
Sources
NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.