Tornadoes · United States · Wisconsin · 2009

EF1 tornado, Saint Croix County, Wisconsin, August 8, 2009

This EF1 tornado ran 5.0 miles across Saint Croix County on August 8, 2009, touching down at 10:24 PM CDT and reaching 450 yards wide. It killed nobody, and did $500,000 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.

  1. EF065 to 85 mph

    Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

  2. EF186 to 110 mphthis tornado

    Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

  3. 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.

  4. 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.

  5. EF4166 to 200 mph

    Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

  6. 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.

  7. 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 8, 2009
Touchdown
10:24 PM CDT (03:24 UTC)
Lifted
10:41 PM CDT (03:41 UTC)
On the ground
17 minutes
Path length
5.0 miles (8.0 km)
Path width
450 yards (411 m)
Deaths
0
Injuries
0
Property damage
$500,000
County
Saint Croix County
Touchdown point
45.038, -92.675
Lift-off point
45.038, -92.573
Record number
0908082124-01

The warnings

23 minutes of warning. NWS MPX issued a tornado warning for this county at 03:01 UTC, 23 minutes before the tornado touched down, in force until 03:30 UTC.

The county was under a tornado watch, issued at 20:53 UTC and running to 05:00 UTC.

Issued (UTC)ExpiredProductOffice
13:37 UTC14:15 UTCSevere Thunderstorm WarningMPX
15:59 UTC16:31 UTCSevere Thunderstorm WarningMPX
20:53 UTC05:00 UTCTornado WatchMPX
02:43 UTC03:15 UTCTornado WarningMPX
03:01 UTC03:30 UTCTornado WarningMPX
03:14 UTC03:45 UTCTornado WarningMPX
03:29 UTC04:15 UTCTornado WarningMPX
04:14 UTC05:00 UTCTornado WarningMPX

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 Slight Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 00:41 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.

Minneapolis, MN (KMPX), 00:00Z

3.4 hours before the tornado, 80 km from the path. August 9, 2009.

Skew-T log-pSkew-T log-p diagram, Minneapolis, MN at 00:00Z on 2009-08-09Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 3715 joules per kilogram, CIN -17, lifted condensation level 841 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Minneapolis, MN at 00:00Z on 2009-08-09The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 190 square meters per square second, 0 to 6 km bulk shear 47 knots.19395878Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
3715 J/kg
Mixed-layer CIN
-17 J/kg
Surface CAPE
5177 J/kg
Mixed-layer LCL
841 m above ground
0-6 km bulk shear
47 kt
0-1 km bulk shear
18 kt
0-1 km storm-relative helicity
190 m²/s²
0-3 km storm-relative helicity
163 m²/s²
Significant tornado parameter
3.8
Supercell composite
16.8
0-3 km lapse rate
5.1 K/km

Open this sounding in Storm Lab

Minneapolis, MN (KMPX), 12:00Z

8.6 hours after it, 80 km from the path. August 9, 2009.

Skew-T log-pSkew-T log-p diagram, Minneapolis, MN at 12:00Z on 2009-08-09Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 277 joules per kilogram, CIN -126, lifted condensation level 543 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Minneapolis, MN at 12:00Z on 2009-08-09The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity -108 square meters per square second, 0 to 6 km bulk shear 49 knots.1939587897Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
277 J/kg
Mixed-layer CIN
-126 J/kg
Surface CAPE
466 J/kg
Mixed-layer LCL
543 m above ground
0-6 km bulk shear
49 kt
0-1 km bulk shear
16 kt
0-1 km storm-relative helicity
-108 m²/s²
0-3 km storm-relative helicity
4 m²/s²
Significant tornado parameter
-0.1
Supercell composite
-0.5
0-3 km lapse rate
4.5 K/km

Open this sounding in Storm Lab

The radar

The Minneapolis radar (KMPX), 77 km away, was scanning. The volume nearest the touchdown began at 03:25 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)ReportWhereCountyRemark
03:03 UTCHAIL 0.5New RichmondSt. Croix, WIREPORTED BY AIRPORT MANAGER.
03:10 UTCFUNNEL CLOUD1 Nw HudsonSt. Croix, WI
03:20 UTCTSTM WND DMG2 N BurkhardtSt. Croix, WINUMEROUS POWER LINES AND TREES TOPPLED IN ST JOSEPH TOWNSHIP NEAR OAKWOOD LANE. HOME OWNER AT 1223 OAKWOOD LANE REPORTED GARAGE RIPPED APART AND BOAT SUCKED AWAY.
03:20 UTCTSTM WND DMG2 Ssw East FarmingtonPolk, WITREE DOWN ACROSS ROAD.
03:25 UTCTSTM WND DMG1 N BurkhardtSt. Croix, WIMAJOR DAMAGE TO 4 HOMES. LOTS OF TREES DOWN. TIME OF EVENT ESTIMATED. DAMAGE SURVEY PLANNED AROUND BOARDMAN AND BURKHARDT.
03:25 UTCTSTM WND DMG3 E East FarmingtonPolk, WITREE DOWN ACROSS ROAD.
03:25 UTCTSTM WND DMG4 E East FarmingtonPolk, WIABOUT SIX TREES DOWNED FROM A DOWNBURST.
03:25 UTCTORNADO1 Nnw BurkhardtSt. Croix, WIDAMAGE SURVEY DETERMINED AN EF-1 TORNADO TOUCHED DOWN AND TRAVELLED FIVE MILES TO TWO MILES SOUTHEAST OF BOARDMAN. NUMEROUS TREES WERE SNAPPED. SEVERAL GARAGES AND A BOAT WERE BLOWN AWAY. TORNADO WAS ACCOMPANIED BY VERY
03:37 UTCHAIL 0.5New RichmondSt. Croix, WIREPORTED BY AIRPORT MANAGER.
03:40 UTCTSTM WND DMG2 N BurkhardtSt. Croix, WINUMEROUS POWER LINES AND TREES TOPPLED IN ST JOSEPH TOWNSHIP NEAR OAKWOOD LANE. HOME OWNER AT 1223 OAKWOOD LANE REPORTED GARAGE RIPPED APART AND BOAT SUCKED AWAY.
03:45 UTCTSTM WND DMG2 Nnw HammondSt. Croix, WIGARAGE DOORS BLOWN IN. PORTION OF A ROOF BLOWN OFF HOUSE. CORN BLOWN DOWN. DAMAGE IN THE AREA OF 167TH STREET. TIME ESTIMATED FROM RADAR.
03:51 UTCTORNADO4 Nnw HammondSt. Croix, WIDAMAGE SURVEY DETERMINED EF-0 TORNADO FOR ABOUT 1/2 MILE. SEVERAL GARAGE DOORS WERE BLOWN IN. PORTION OF A ROOF BLOWN OFF HOUSE. NUMEROUS SOFFETS BLOWN OFF. CORN BLOWN DOWN. DAMAGE IN THE AREA OF 167TH STREET. TIME ESTIM
04:11 UTCTSTM WND DMGBoardmanSt. Croix, WIDAMAGE SURVEY PLANNED AROUND BOARDMAN AND BURKHARDT.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

This ground now

The live radar over the trackEvery 2009 tornado in WisconsinEvery tornado in Wisconsin since 1950Warnings in force in Wisconsin nowThe forecast where you are

The other tornadoes of August 8, 2009

3 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 88:33 PM CDTEF1Hennepin, MN9.1200$1.0 million
August 89:02 PM MDTEF0Weld, CO0.150
August 810:51 PM CDTEF0Saint Croix, WI0.350$100,000

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.