Tornadoes · United States · Minnesota · 2007

EF0 tornado, Dennison, Minnesota, May 23, 2007

Name: EF0 tornado, Dennison, Minnesota, May 23, 2007
Start: 2007-05-23T21:10:00.000Z
End: 2007-05-23T21:15:00.000Z
Location: Dennison, Minnesota

This EF0 tornado ran 2.0 miles across Goodhue County on May 23, 2007, touching down at 4:10 PM CDT and reaching 50 yards wide. It killed nobody.

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 mphthis tornado
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
EF186 to 110 mph
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: EF0
Date: May 23, 2007
Touchdown: 4:10 PM CDT (21:10 UTC)
Lifted: 4:15 PM CDT (21:15 UTC)
On the ground: 5 minutes
Path length: 2.0 miles (3.2 km)
Path width: 50 yards (46 m)
Deaths: 0
Injuries: 0
County: Goodhue County
Touchdown point: 44.369, -92.959
Lift-off point: 44.392, -92.936
Record number: 0705231510-01

What the Weather Service recorded

Frontal boundary induced severe weather episode.

NWS damage survey confirmed a weak tornado. It mostly crossed open fields, but did knock down several dozen trees, and caused minor structural damage at two farms.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

The forecast that day

The Storm Prediction Center had this point in a Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 20:06 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.

What forecasters said that day

The local office's own words before the tornado touched down, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Twin Cities, MN wrote its last area forecast discussion before the tornado touched down at May 23, 4:02 PM CDT, 8 minutes earlier.

Area forecast discussion, May 23, 4:02 PM CDT, 8 minutes before

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Hazardous weather outlook, May 23, 2:35 PM CDT, 1 hour 35 minutes before

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
235 PM CDT WED MAY 23 2007

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
240745-
DOUGLAS-TODD-MORRISON-MILLE LACS-KANABEC-STEVENS-POPE-STEARNS-
BENTON-SHERBURNE-ISANTI-CHISAGO-LAC QUI PARLE-SWIFT-CHIPPEWA-
KANDIYOHI-MEEKER-WRIGHT-HENNEPIN-ANOKA-RAMSEY-WASHINGTON-
YELLOW MEDICINE-RENVILLE-MCLEOD-SIBLEY-CARVER-SCOTT-DAKOTA-
REDWOOD-BROWN-NICOLLET-LE SUEUR-RICE-GOODHUE-WATONWAN-BLUE EARTH-
WASECA-STEELE-MARTIN-FARIBAULT-FREEBORN-POLK-BARRON-RUSK-
ST. CROIX-PIERCE-DUNN-PEPIN-EAU CLAIRE-
235 PM CDT WED MAY 23 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL AND
SOUTH CENTRAL MINNESOTA...AND WEST CENTRAL WISCONSIN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED THIS
AFTERNOON INTO THIS EVENING...ESPECIALLY ACROSS CENTRAL AND SOUTH CENTRAL
MINNESOTA AND WEST CENTRAL WISCONSIN. THESE THUNDERSTORMS WILL BE
CAPABLE OF PRODUCING VERY LARGE HAIL...DAMAGING WINDS...AND
ISOLATED TORNADOES.

ADDITIONAL SHOWERS AND THUNDERSTORMS WILL DEVELOP AFTER
MIDNIGHT...SPREADING NORTHWARD INTO SOUTHWESTERN AND SOUTH CENTRAL
MINNESOTA. HEAVY RAIN AND FLOODING WILL BE POSSIBLE...MAINLY TO
THE SOUTH AND WEST OF THE MINNESOTA RIVER VALLEY...AND ALONG THE
INTERSTATE 90 CORRIDOR.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE THREAT FOR HEAVY RAIN AND FLOODING WILL CONTINUE THROUGH THE
MORNING HOURS ON THURSDAY.

A SLIGHT RISK OF SEVERE THUNDERSTORMS EXISTS THURSDAY AFTERNOON
AND EVENING ACROSS PORTIONS OF EASTERN MINNESOTA AND WEST CENTRAL
WISCONSIN...MAINLY TO THE EAST OF A LINE FROM LAKE MILLE LACS TO
ALBERT LEA. LARGE HAIL...DAMAGING WINDS...AND HEAVY RAIN WILL BE
THE MAIN THREATS.

ADDITIONAL THUNDERSTORMS WILL BE POSSIBLE THIS WEEKEND. CONTINUE
TO MONITOR FUTURE FORECASTS OVER THE NEXT COUPLE OF DAYS FOR
DETAILS ON THE WEEKEND STORMS.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION WILL BE NEEDED THIS AFTERNOON...MAINLY
EAST OF A SAUK CENTRE TO ST JAMES LINE.

In the hours before

Special weather statement, May 23, 1:40 PM CDT, 2 hours 30 minutes before

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
140 PM CDT WED MAY 23 2007

MNZ044-049>053-057>063-065>070-074>078-082>085-091>093-WIZ014>016-
023>028-232130-
ANOKA-BARRON-BENTON-BLUE
EARTH-BROWN-CARVER-CHIPPEWA-CHISAGO-DAKOTA-DUNN-EAU
CLAIRE-FARIBAULT-FREEBORN-GOODHUE-HENNEPIN-ISANTI-KANDIYOHI-LE
SUEUR-MARTIN-MCLEOD-MEEKER-MILLE
LACS-NICOLLET-PEPIN-PIERCE-POLK-RAMSEY-RENVILLE-RICE-RUSK-SCOTT-
SHERBURNE-SIBLEY-ST.
CROIX-STEARNS-STEELE-WASECA-WASHINGTON-WATONWAN-WRIGHT-
140 PM CDT WED MAY 23 2007

...SIGNIFICANT WEATHER ALERT FOR MILLE LACS...STEARNS...ISANTI...
CHISAGO...SHERBURNE...WRIGHT...ANOKA...KANDIYOHI...MEEKER...
WASHINGTON...HENNEPIN...RAMSEY...MCLEOD...CARVER...DAKOTA...
RENVILLE...SCOTT...SIBLEY...GOODHUE...LE SUEUR...RICE...BROWN...
NICOLLET...BLUE EARTH...WASECA...STEELE...WATONWAN...FARIBAULT...
FREEBORN...MARTIN...BENTON...POLK...BARRON...RUSK...CHIPPEWA...
ST. CROIX...DUNN...PIERCE...EAU CLAIRE AND PEPIN COUNTIES UNTIL 430
PM CDT...

AT 140 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
NUMEROUS STORMS ACROSS PORTIONS OF SOUTH CENTRAL...CENTRAL AND EAST
CENTRAL MINNESOTA... AS WELL AS WEST CENTRAL WISCONSIN.

THE STORMS WILL TYPICALLY DEVELOP QUICKLY IN ANY OF THESE
AREAS...PRODUCE HEAVY RAIN FOR TEN OR TWENTY MINUTES...THEN WEAKEN.
HAIL AS BIG AS ONE HALF INCH IS ALSO POSSIBLE FOR A BRIEF TIME.
LIGHTNING SHOULD ALSO BE EXPECTED.

LOCATIONS THAT MAY BE AFFECTED INCLUDE THE TWIN CITIES METRO...
MANKATO... HUTCHINSON...ST CLOUD... CAMBRIDGE...EAU CLAIRE...
LADYSMITH AND RICE LAKE.

TDK

Local storm report, May 23, 2:22 PM CDT, 1 hour 48 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
222 PM CDT WED MAY 23 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0210 PM     TSTM WND DMG     PLYMOUTH                45.02N 93.46W
05/23/2007                   HENNEPIN           MN   TRAINED SPOTTER

            SEMI TRAILOR TIPPED OVER IN PLYMOUTH AT HIGHWAY 55 AND
            494. SPOTTER SAID HE WITNESSED A DOWNBURST.

0210 PM     HAIL             PLYMOUTH                45.02N 93.46W
05/23/2007  E0.88 INCH       HENNEPIN           MN   TRAINED SPOTTER

&&

RJN

Local storm report, May 23, 2:26 PM CDT, 1 hour 44 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
226 PM CDT WED MAY 23 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0226 PM     HAIL             BROOKLYN PARK           45.11N 93.35W
05/23/2007  E2.50 INCH       HENNEPIN           MN   TRAINED SPOTTER

&&

RJN

Local storm report, May 23, 2:34 PM CDT, 1 hour 36 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
234 PM CDT WED MAY 23 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0230 PM     HAIL             CRYSTAL                 45.04N 93.36W
05/23/2007  E1.75 INCH       HENNEPIN           MN   TRAINED SPOTTER

            NEAR CRYSTAL AIRPORT

&&

RJN

Local storm report, May 23, 3:15 PM CDT, 55 minutes before

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
315 PM CDT WED MAY 23 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0210 PM     TSTM WND DMG     PLYMOUTH                45.02N 93.46W
05/23/2007                   HENNEPIN           MN   TRAINED SPOTTER

            SEMI TRAILOR TIPPED OVER IN PLYMOUTH AT HIGHWAY 55 AND
            494. SPOTTER SAID HE WITNESSED A DOWNBURST.

0210 PM     HAIL             PLYMOUTH                45.02N 93.46W
05/23/2007  E0.88 INCH       HENNEPIN           MN   TRAINED SPOTTER

0210 PM     TSTM WND DMG     PLYMOUTH                45.02N 93.46W
05/23/2007                   HENNEPIN           MN   TRAINED SPOTTER

            DAMAGE TO ROOF OF COMMERCIAL BUILDING ON BOONE AVE N.
            TREES IN NEARBY VICINITY UP TO ONE FOOT DIAMETER WERE
            DOWNED OR BLOW OVER. TIME WAS ESIMATED.

0215 PM     HAIL             CRYSTAL                 45.04N 93.36W
05/23/2007  E2.00 INCH       HENNEPIN           MN   TRAINED SPOTTER

            MAINLY 1 TO 1.5 INCH STONES. BIGGEST HAIL EGG SIZED.

0225 PM     HAIL             BROOKLYN PARK           45.11N 93.35W
05/23/2007  E1.75 INCH       HENNEPIN           MN   TRAINED SPOTTER

0225 PM     TSTM WND DMG     BROOKLYN PARK           45.11N 93.35W
05/23/2007                   HENNEPIN           MN   TRAINED SPOTTER

            TREE LIMBS DOWN

0226 PM     HAIL             BROOKLYN PARK           45.11N 93.35W
05/23/2007  E2.50 INCH       HENNEPIN           MN   TRAINED SPOTTER

0230 PM     HAIL             CRYSTAL                 45.04N 93.36W
05/23/2007  E1.75 INCH       HENNEPIN           MN   TRAINED SPOTTER

            NEAR CRYSTAL AIRPORT

0230 PM     HAIL             BROOKLYN PARK           45.11N 93.35W
05/23/2007  E0.88 INCH       HENNEPIN           MN   TRAINED SPOTTER

            NEAR ZANE AND CO RD 30

0236 PM     HAIL             SPRING LAKE PARK        45.12N 93.25W
05/23/2007  E1.00 INCH       ANOKA              MN   TRAINED SPOTTER

&&

RJN

Local storm report, May 23, 3:57 PM CDT, 13 minutes before

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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), 12:00Z

9.2 hours before the tornado, 73 km from the path. May 23, 2007.

Skew-T log-p

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.

Hodograph

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: 84 J/kg
Mixed-layer CIN: -48 J/kg
Surface CAPE: 33 J/kg
Mixed-layer LCL: 811 m above ground
0-6 km bulk shear: 40 kt
0-1 km bulk shear: 30 kt
0-1 km storm-relative helicity: 141 m²/s²
0-3 km storm-relative helicity: 164 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0
0-3 km lapse rate: 6.2 K/km

Open this sounding in Storm Lab

The surface observations

Stanton Airfield (SYN), 12 km from the path, in the two hours either side.

Time (UTC)	Temp (°F)	Dew point (°F)	Wind	Gust (kt)	Pressure (mb)	Weather
00:00 UTC

From the Iowa Environmental Mesonet's archive of airport observations.

The radar

The Minneapolis radar (KMPX), 71 km away, was scanning. The volume nearest the touchdown began at 21:10 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.

This ground now

The live radar over the track Every 2007 tornado in Minnesota Every tornado in Minnesota since 1950 Warnings in force in Minnesota now The forecast where you are

The other tornadoes of May 23, 2007

16 more were confirmed in the United States that day.

Date	Time	Rating	Where	Path (mi)	Width (yd)	Damage
May 23	4:28 PM CDT	EF0	Roberts, TX	0.2	25
May 23	5:25 PM CDT	EF0	Ochiltree, TX	1.0	50
May 23	5:39 PM CDT	EF0	Ochiltree, TX	1.0	50
May 23	5:56 PM CDT	EF0	Lipscomb, TX	1.0	50	$6,000
May 23	6:14 PM CDT	EF0	Ochiltree, TX	2.0	50
May 23	6:40 PM CDT	EF0	Edwards, KS	0.6	30
May 23	6:40 PM CDT	EF0	Ochiltree, TX	2.0	50
May 23	6:42 PM CDT	EF0	Edwards, KS	1.3	50
May 23	7:39 PM CDT	EF0	Lipscomb, TX	2.0	50
May 23	8:15 PM CDT	EF0	Hutchinson, TX	0.1	25
May 23	8:17 PM CDT	EF0	Hutchinson, TX	0.1	50
May 23	9:28 PM CDT	EF0	Roberts, TX	2.0	100
May 23	9:43 PM CDT	EF1	Ochiltree, TX	3.0	880	$9,000
May 23	10:40 PM CDT	EF2	Lipscomb, TX	7.0	440	$23,000
May 23	10:55 PM CDT	EF1	Lipscomb, TX	4.0	150	$13,000
May 23	11:11 PM CDT	EF2	Lipscomb, TX	8.0	528	$36,000

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.