Tornadoes · United States · North Dakota · 2011

EF1 tornado, Rugby, North Dakota, July 20, 2011

This EF1 tornado ran 1.3 miles across Pierce County on July 20, 2011, touching down at 6:50 AM CDT and reaching 50 yards wide. It killed nobody, and did $325,000 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
July 20, 2011
Touchdown
6:50 AM CDT (11:50 UTC)
Lifted
6:55 AM CDT (11:55 UTC)
On the ground
5 minutes
Path length
1.3 miles (2.0 km)
Path width
50 yards (46 m)
Deaths
0
Injuries
0
Property damage
$325,000
Crop damage
$150,000
County
Pierce County
Touchdown point
48.300, -100.000
Lift-off point
48.311, -99.978
Record number
1107200550-01

What the Weather Service recorded

Early morning thunderstorms developed and intensified across north central into northeastern North Dakota in response to a strengthening low level jet and in advance of a strong surface cold front. Storms initially were elevated with several reports of strong thunderstorm wind gusts. A bowing structure developed with one confirmed tornado on the leading edge of the storm near Rugby. Additional reports of strong winds followed the tornado, with the storms eventually moving east out of the Bismarck County Warning Area.

A brief tornado touched down five miles south of Rugby on the leading edge of a linear severe thunderstorm. This tornado was within a larger area of straight line thunderstorm winds which also caused damage. Several buildings sustained damage or were destroyed by this tornado, along with trees, and three power poles were snapped along North Dakota Highway 3 where the tornado crossed. A semi truck was picked up along Highway 3 and thrown into the ditch. There were no injuries or deaths reported with this tornado. The tornado damage corresponded to EF1 on the Enhanced Fujita Scale. From that it was determined that wind speeds with this tornado were on the order of 100 miles per hour.

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

The warnings

16 minutes of warning. NWS BIS issued a tornado warning for this county at 11:34 UTC, 16 minutes before the tornado touched down, in force until 12:00 UTC.

The county was under a severe thunderstorm watch, issued at 10:25 UTC and running to 14:10 UTC.

Issued (UTC)ExpiredProductOffice
10:25 UTC14:10 UTCSevere Thunderstorm WatchBIS
11:22 UTC12:15 UTCSevere Thunderstorm WarningBIS
11:34 UTC12:00 UTCTornado WarningBIS
12:05 UTC12:45 UTCSevere Thunderstorm WarningBIS

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 05:47 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.

Bismarck Municip, ND (KBIS), 00:00Z

11.8 hours before the tornado, 179 km from the path. July 20, 2011.

Skew-T log-pSkew-T log-p diagram, Bismarck Municip, ND at 00:00Z on 2011-07-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 5088 joules per kilogram, CIN -73, lifted condensation level 1472 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, Bismarck Municip, ND at 00:00Z on 2011-07-20The 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 -4 square meters per square second, 0 to 6 km bulk shear 29 knots.193958Sfc1 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
5088 J/kg
Mixed-layer CIN
-73 J/kg
Surface CAPE
6712 J/kg
Mixed-layer LCL
1472 m above ground
0-6 km bulk shear
29 kt
0-1 km bulk shear
1 kt
0-1 km storm-relative helicity
-4 m²/s²
0-3 km storm-relative helicity
95 m²/s²
Significant tornado parameter
0.4
Supercell composite
5.9
0-3 km lapse rate
7.2 K/km

Open this sounding in Storm Lab

Bismarck Municip, ND (KBIS), 12:00Z

0.2 hours after it, 179 km from the path. July 20, 2011.

Skew-T log-pSkew-T log-p diagram, Bismarck Municip, ND at 12:00Z on 2011-07-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 3591 joules per kilogram, CIN -141, lifted condensation level 1254 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, Bismarck Municip, ND at 12:00Z on 2011-07-20The 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 -7 square meters per square second, 0 to 6 km bulk shear 41 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
3591 J/kg
Mixed-layer CIN
-141 J/kg
Surface CAPE
4656 J/kg
Mixed-layer LCL
1254 m above ground
0-6 km bulk shear
41 kt
0-1 km bulk shear
21 kt
0-1 km storm-relative helicity
-7 m²/s²
0-3 km storm-relative helicity
101 m²/s²
Significant tornado parameter
0.5
Supercell composite
15.4
0-3 km lapse rate
4.9 K/km

Open this sounding in Storm Lab

The surface observations

Rugby (RUG), 10 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
12:15 UTC71.664.460° 16 kt19995.9+TSRA
12:35 UTC71.664.440° 10 kt21995.9VCTS
12:55 UTC71.666.290° 4 kt996.3
13:15 UTC71.66890° 3 kt995.9
13:35 UTC71.668210° 12 kt997

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

What was reported nearby

Local storm reports within 60 km of the path, in the three hours either side.

Time (UTC)ReportWhereCountyRemark
11:45 UTCTSTM WND DMG5 Nw BaltaPierce, NDBOX ELDER TREES TOPPLED. BENT FLAGPOLE
11:50 UTCTORNADO5 S RugbyPierce, NDSANITATION BUILDING LEVELED. THREE POWER POLES SW OF THE SANITATION BUILDING SNAPPED MIDWAY UP AND A LOT OF TREENS STRIPPED. HAYBALES SCATTERED WITH SOME RIPPED APART. SEMI TRUCK PICKED UP ALONG ND HIGHWAY 3 AND THROWN I
11:50 UTCTSTM WND DMGPleasant LakeBenson, NDSTEEL POLE BARN DESTROYED
11:52 UTCTSTM WND GST 0RugbyPierce, NDWIND ESTIMATED AT 70 MPH.
11:52 UTCTSTM WND GST 70RugbyPierce, ND
11:55 UTCTSTM WND DMG5 E RugbyPierce, NDSTRAIGHT LINE WINDS ESTIMATED TO 75 MPH. 60 FOOT SPRUCE TREES DOWN. HEAVY RAIN 0.80 INCHES.
11:55 UTCTSTM WND DMG1 Nw KnoxBenson, ND5-10 INCH DIAMTER BRANCHES DOWN.
11:55 UTCTSTM WND DMG1 Se KnoxBenson, ND40-50 FOOT TALL TREES DOWN.
11:55 UTCTSTM WND DMG1 W KnoxBenson, ND4-6 INCH DIAMATER BRANCHES DOWN. GRAIN ELEVATOR DOORS BLOWN OFF.
11:55 UTCTSTM WND DMGNw KnoxBenson, ND5-10 INCH DIAMTER BRANCHES DOWN.
11:55 UTCTSTM WND DMGSe KnoxBenson, ND40-50 FOOT TALL TREES DOWN.
11:55 UTCTSTM WND DMGW KnoxBenson, ND4-6 INCH DIAMATER BRANCHES DOWN. GRAIN ELEVATOR DOORS BLOWN OFF.
11:56 UTCTSTM WND GST 68RugbyPierce, NDMEASURED WIND GUST AT RUGBY AWOS.
12:25 UTCHIGH SUST WINDS 54.142 Ese LeedsBenson, NDTHE 2 MINUTE AVERAGED WIND RECORDED AT THE LEEDS WIND PROFILER.

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

This ground now

The live radar over the trackEvery 2011 tornado in North DakotaEvery tornado in North Dakota since 1950Warnings in force in North Dakota nowThe forecast where you are

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.