Tornadoes · United States · Minnesota · 2010

EF0 tornado, Little Rock, Minnesota, July 17, 2010

Name: EF0 tornado, Little Rock, Minnesota, July 17, 2010
Start: 2010-07-17T23:50:00.000Z
End: 2010-07-17T23:53:00.000Z
Location: Little Rock, Minnesota

This EF0 tornado ran 1.4 miles across Morrison County on July 17, 2010, touching down at 6:50 PM CDT and reaching 30 yards wide. It killed nobody, and did $250,000 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 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: July 17, 2010
Touchdown: 6:50 PM CDT (23:50 UTC)
Lifted: 6:53 PM CDT (23:53 UTC)
On the ground: 3 minutes
Path length: 1.4 miles (2.2 km)
Path width: 30 yards (27 m)
Deaths: 0
Injuries: 0
Property damage: $250,000
County: Morrison County
Touchdown point: 45.859, -94.046
Lift-off point: 45.841, -94.034
Record number: 1007171750-01

What the Weather Service recorded

The atmosphere became very unstable Saturday afternoon, and along with a strong wind shear, aided in the development of very large hail, isolated tornadoes and significant straight-line wind damage. ||The first storm developed near Alexandria and moved southeast along Interstate 94 before dying in the southwest part of the Twin Cities late that afternoon. Numerous reports of very large hail, up to the size of softballs, occurred near St. Cloud, southeast to Watertown. ||The next area of severe storms developed across central Minnesota, and far west-central Minnesota and moved east and southeast toward east-central Minnesota where a strong bow echo developed and moved across the northern portion of the Twin Cities Metropolitan Area. ||There was widespread damage along the leading edge of this bow echo where numerous trees, power lines and homes were either uprooted, blown down, or destroyed. ||These storms moved into west-central Wisconsin and also caused damage to trees before weakening toward the late evening.

Several dozen trees were downed, two sheds and a barn were damaged, and minor damage occurred to a house.

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

The warnings

25 minutes of warning. NWS MPX issued a tornado warning for this county at 23:25 UTC, 25 minutes before the tornado touched down, in force until 00:15 UTC.

The county was under a tornado watch, issued at 17:28 UTC and running to 01:41 UTC.

Issued (UTC)	Expired	Product	Office
17:28 UTC	01:41 UTC	Tornado Watch	MPX
22:10 UTC	23:15 UTC	Tornado Warning	MPX
22:49 UTC	23:30 UTC	Tornado Warning	MPX
23:25 UTC	00:15 UTC	Tornado Warning	MPX
23:54 UTC	00:45 UTC	Tornado Warning	MPX
00:13 UTC	01:15 UTC	Tornado Warning	MPX

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 Moderate Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 20:00 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.

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 Jul 17, 6:05 PM CDT, 45 minutes earlier.

Area forecast discussion, Jul 17, 6:05 PM CDT, 45 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
605 PM CDT SAT JUL 17 2010

.DISCUSSION...
THE MAIN FORECAST CHALLENGE IS THE SEVERE WEATHER OCCURRING OVER THE
AREA THIS AFTERNOON INTO THIS EVENING. AIRMASS WAS VERY PRIMED FOR
THE DEVELOPMENT OF SUPERCELL ACROSS MUCH OF FORECAST AREA.  THIS
THE MAIN FOCUS WILL BE OVER WESTERN INTO SOUTH CENTRAL MINNESOTA.
WEAK CAP OVER SOUTHWEST MN...EXPECTED TO ERODE BY LATE AFTERNOON OR
EARLY THIS EVENING.

THUNDERSTORMS CONTINUE TO FIRE ALONG AND NORTH OF WARM FRONT
BOUNDARY OVER CENTRAL MN. MOST OF THE THUNDERSTORMS HAVE BEEN
ELEVATED...SO THE MAIN THREATS OVER OUR AREA THIS AFTERNOON WILL BE
LARGE HAIL AND DAMAGING WINDS.  ONCE THE CAP ERODE NEAR THE WARM
SECTOR SOUTH INTERSTATE 94...EXPECT SOME ISOLATED TORNADOES TO
DEVELOP.

THUNDERSTORM ACTIVITY IS EXPECTED TO DEVELOP INTO A MESOSCALE
CONVECTIVE SYSTEM OVER SOUTHERN MN...WITH MOVES THE BULK OF THE
SEVERE WEATHER BY 10 PM SOUTH OF OUR CWA.  LATER TONIGHT...MORE OF
HEAVY RAIN THREAT AS A SERIES OF SHORT WAVES MOVE ACROSS THE AREA
OVERNIGHT.

MOST OF THE SHOWERS AND THUNDERSTORMS SHOULD BE OUT OF OUR FORECAST
AREA BY MIDNIGHT...EXCEPT OVER PARTS OF WEST CENTRAL WI AND EXTREME
SOUTH CENTRAL MN.

HYDROLOGICAL CONCERNS...THUNDERSTORMS ARE EXPECTED TO TRAIN OVER
PARTS OF WEST CENTRAL INTO SOUTH CENTRAL MN TONIGHT. SEVERAL WEAK
SHORTWAVE TROUGHS MOVING OVER THE UPPER MIDWEST TONIGHT...EXPECT A
BACKWARD PROPAGATING MESOSCALE CONVECTIVE COMPLEX TO DEVELOPS OVER
WESTERN MN LATER THIS EVENING. PRECIP WATER VALUES OF 2.00 TO 2.50
INCHES ARE FORECAST OVER THIS AREA. EVEN WITH FORECAST QPF 3.00 OR
4.00 INCHES. IT SHOULD NOT BE A PROBLEM ON THE MAIN STEMS OF THE
RIVERS TONIGHT.

NEXT CHANCE OF THUNDERSTORMS IS MONDAY AS ANOTHER WEAK SHORT WAVE
TROUGH.

LONG RANGE FORECAST...MODELS DIFFER ON THE THREAT OF PRECIPITATION
FOR THE UPPER MIDWEST THROUGH END OF THE WORK WEEK.  GFS MODEL KEEPS
MUCH OF THE FORECAST AREA DRY...WHILE THE PERSISTENT EUROPEAN MODEL
KEEPS US WET THROUGH FRIDAY.  WL LEAN MORE TOWARDS THE EUROPEAN
MODEL...AS SEVERAL MINOR IMPULSES RIDE OVER THE UPPER RIDGE OVER THE
UPPER MIDWEST. TIMING OF THE INITIATION OF THUNDERSTORMS WILL BE
CRITICAL.

&&

.AVIATION.../00Z TAF ISSUANCE/

WITH COLD FRONT STILL WEST OF MOST OF THE TAF SITES EARLY THIS
EVENING. THUNDERSTORMS...SOME SEVERE ARE POSSIBLE TONIGHT.  THE
LATEST IR SATELLITE LOOP SHOWED A LINE OF THUNDERSTORMS WITH A
COUPLE OF MESOSCALE CONVECTIVE COMPLEXES OVER EASTERN SOUTH DAKOTA
AND WESTERN MINNESOTA. WEATHER CONDS WILL LOWER TO MARGINAL TO IFR
CONDS IN AND NEAR THUNDERSTORMS AS THESE SYSTEMS COME ACROSS THE
AREA OVERNIGHT.  ONCE THE STORMS EXIT THE AREA LATE TONIGHT AND
EARLY SUNDAY MORNING...CONDS WILL IMPROVE TO SCATTERED TO BROKEN
CLOUDS ROUGHLY BETWEEN 4000-5000 FEET AGL.

KMSP...FRONTAL BOUNDARY OVER EASTERN SODAK WILL MOVE EAST THROUGH
THE METRO AREA OVERNIGHT.  WEATHER CONDS EXPECTED TO IMPROVE AFTER
MIDNIGHT. WINDS SOUTHEAST TO SOUTH 10 TO 20 KNOTS...THEN SHIFTING TO
NORTHWEST 10 TO 15 KNOTS AFTER THE FRONTAL PASSAGE.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

Hazardous weather outlook, Jul 17, 11:44 AM CDT, 7 hours 6 minutes before

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1144 AM CDT SAT JUL 17 2010

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
180915-
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-
1144 AM CDT SAT JUL 17 2010

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

THE ENTIRE AREA REMAINS UNDER A MODERATE RISK OF SEVERE
THUNDERSTORMS. THUNDERSTORMS ARE EXPECTED TO DEVELOP IN WEST CENTRAL
AND CENTRAL MINNESOTA THIS AFTERNOON...WITH SOME OF THESE STORMS
LIKELY BECOMING SEVERE. THUNDERSTORMS ARE EXPECTED TO BECOME MORE
WIDESPREAD ACROSS THE AREA THIS EVENING. INITIALLY THE PRIMARY
THREAT WILL BE LARGE HAIL WITH A FEW TORNADOES POSSIBLE. DURING THE
EVENING AND INTO THE OVERNIGHT THE PRIMARY THREAT WILL BECOME
DAMAGING WINDS AND HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE WEEK AHEAD LOOKS LIKE A CONTINUATION OF AN ACTIVE WEATHER PATTERN
WITH THUNDERSTORMS ALREADY RETURNING BY MONDAY.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION WILL LIKELY BE NEEDED THIS AFTERNOON AND
INTO TONIGHT.

In the hours before

Local storm report, Jul 17, 6:30 PM CDT, 20 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
630 PM CDT SAT JUL 17 2010

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

0433 PM     HAIL             HOWARD LAKE             45.06N 94.09W
07/17/2010  E1.00 INCH       WRIGHT             MN   TRAINED SPOTTER

&&

DFC

Local storm report, Jul 17, 6:34 PM CDT, 16 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
634 PM CDT SAT JUL 17 2010

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

0630 PM     HAIL             LITTLE FALLS            45.98N 94.36W
07/17/2010  E1.75 INCH       MORRISON           MN   LAW ENFORCEMENT

&&

DFC

Local storm report, Jul 17, 6:36 PM CDT, 14 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
636 PM CDT SAT JUL 17 2010

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

0630 PM     HAIL             5 N LITTLE FALLS        46.04N 94.35W
07/17/2010  E1.00 INCH       MORRISON           MN   TRAINED SPOTTER

            HAIL LASTED FOR APPROX 5 MINUTES AND COVERED THE GROUND

&&

DFC

Local storm report, Jul 17, 6:40 PM CDT, 10 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
640 PM CDT SAT JUL 17 2010

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

0633 PM     TSTM WND GST     BENSON                  45.32N 95.61W
07/17/2010  M58 MPH          SWIFT              MN   ASOS

&&

DFC

Local storm report, Jul 17, 6:42 PM CDT, 8 minutes before

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
642 PM CDT SAT JUL 17 2010

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

0535 PM     HAIL             STAPLES                 46.36N 94.80W
07/17/2010  E2.75 INCH       TODD               MN   LAW ENFORCEMENT

0535 PM     TSTM WND DMG     STAPLES                 46.36N 94.80W
07/17/2010                   TODD               MN   LAW ENFORCEMENT

            TREES DOWN

&&

JLM

Local storm report, Jul 17, 6:48 PM CDT, 2 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
648 PM CDT SAT JUL 17 2010

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

0643 PM     HAIL             3 WNW GENOLA            45.98N 94.17W
07/17/2010  E1.00 INCH       MORRISON           MN   TRAINED SPOTTER

&&

JLM

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

11.8 hours before the tornado, 116 km from the path. July 17, 2010.

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: 368 J/kg
Mixed-layer CIN: -101 J/kg
Surface CAPE: 0 J/kg
Mixed-layer LCL: 1285 m above ground
0-6 km bulk shear: 31 kt
0-1 km bulk shear: 15 kt
0-1 km storm-relative helicity: 119 m²/s²
0-3 km storm-relative helicity: 226 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.9
0-3 km lapse rate: 4.3 K/km

Open this sounding in Storm Lab

Minneapolis, MN (KMPX), 00:00Z

0.2 hours after it, 116 km from the path. July 18, 2010.

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

Mixed-layer CAPE: 1779 J/kg
Mixed-layer CIN: -139 J/kg
Surface CAPE: 2286 J/kg
Mixed-layer LCL: 1367 m above ground
0-6 km bulk shear: 51 kt
0-1 km bulk shear: 28 kt
0-1 km storm-relative helicity: 268 m²/s²
0-3 km storm-relative helicity: 618 m²/s²
Significant tornado parameter: 1.1
Supercell composite: 4.3
0-3 km lapse rate: 5.3 K/km

Open this sounding in Storm Lab

The surface observations

Little Falls (LXL), 26 km from the path, in the two hours either side.

Time (UTC)	Temp (°F)	Dew point (°F)	Wind	Gust (kt)	Pressure (mb)	Weather
21:54 UTC	73.4	64.4	100° 12 kt	18	1008.8
22:14 UTC	73.4	64.4	110° 6 kt		1008.5
22:34 UTC	73.4	62.6	100° 8 kt	15	1008.1
22:54 UTC	71.6	62.6	110° 10 kt	15	1007.8
23:14 UTC	71.6	62.6	110° 12 kt	17	1007.1
23:35 UTC	69.8	60.8	340° 10 kt	19	1010.5	+RA
23:54 UTC	64.4	60.8	40° 8 kt	17	1008.8	+RA
00:14 UTC	64.4	60.8	50° 7 kt		1010.2	RA
00:34 UTC	64.4	62.6	60° 8 kt	22	1012.2	+RA
00:54 UTC	62.6	60.8	60° 7 kt	16	1012.2	RA
01:14 UTC	62.6	60.8	80° 9 kt	15	1011.9	-RA
01:34 UTC	62.6	60.8	80° 13 kt	21	1008.8	-RA

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

The radar

The Minneapolis radar (KMPX), 117 km away, was scanning. The volume nearest the touchdown began at 23:51 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
23:00 UTC	TSTM WND DMG	2 N Fort Ripley	Crow Wing, MN	TWO LARGE OAK TREES BLOWN DOWN...OTHER SMALL TREES DAMAGED.
23:25 UTC	HAIL 0.75	Fort Ripley	Crow Wing, MN
23:30 UTC	HAIL 1	5 N Little Falls	Morrison, MN	HAIL LASTED FOR APPROX 5 MINUTES AND COVERED THE GROUND
23:30 UTC	HAIL 1.75	Little Falls	Morrison, MN
23:43 UTC	HAIL 1	3 Wnw Genola	Morrison, MN
23:56 UTC	TSTM WND GST 81	2 S Buckman	Morrison, MN	ALONG HWY 27
23:58 UTC	TORNADO	1 S Cushing	Morrison, MN	ON GROUND
00:25 UTC	TORNADO	3 E Foreston	Mille Lacs, MN	ROPE TORNADO TOUCHED GROUND BRIEFLY THEN WENT BACK UP
00:46 UTC	FUNNEL CLOUD	Sartell	Stearns, MN	MOVING INTO BENTON COUNTY
01:01 UTC	TSTM WND DMG	3 Ne Hasty	Sherburne, MN	TREES DOWN...DESTROYED FARM IRRIGATION SYSTEM.
01:14 UTC	TSTM WND DMG	Big Lake	Sherburne, MN	6 INCH TREES DOWN
01:15 UTC	TSTM WND DMG	5 S Clearwater	Wright, MN	LARGE GROVE OF TREES DOWNED UP TO 2 FEET IN DIAMETER WITH MINOR DAMAGE TO HOUSE
01:48 UTC	TSTM WND DMG	3 Nw Becker	Sherburne, MN	13 TO 15 LARGE TREES UPROOTED

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

This ground now

The live radar over the track Every 2010 tornado in Minnesota Every tornado in Minnesota since 1950 Warnings in force in Minnesota now The forecast where you are

The other tornadoes of July 17, 2010

6 more were confirmed in the United States that day.

Date	Time	Rating	Where	Path (mi)	Width (yd)	Damage
July 17	5:12 PM CDT	EF0	Wadena, MN	0.4	15
July 17	7:30 PM CDT	EF0	Stearns, MN	0.1	30	$50,000
July 17	7:48 PM CDT	EF0	Wright, MN	4.2	50	$100,000
July 17	8:22 PM CDT	EF0	Murray, MN	0.5	50
July 17	8:23 PM CDT	EF0	Lincoln, NE	0.1	5
July 17	8:44 PM CDT	EF0	Washington, MN	5.2	50	$50,000

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.