Tornadoes · United States · Nebraska · 2011

EF0 tornado, Harrison, Nebraska, May 9, 2011

This EF0 tornado ran 0.0 miles across Sioux County on May 9, 2011, touching down at 6:35 PM MDT and reaching 20 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.

  1. EF065 to 85 mphthis tornado

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

  2. EF186 to 110 mph

    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
EF0
Date
May 9, 2011
Touchdown
6:35 PM MDT (00:35 UTC)
Path length
0.0 miles (0.0 km)
Path width
20 yards (18 m)
Deaths
0
Injuries
0
County
Sioux County
Touchdown point
42.680, -103.791
Lift-off point
42.680, -103.791
Record number
1105091835-01

What the Weather Service recorded

Strong upper impulse moving northeastward from the central Rockies to the High Plains interacted with upslope flow with moist unstable air to produce large hail and a tornado during the late afternoon of May 9.

Brief touchdown in open area with no damage reported.

Report received from 911 operator that public reported tornado, storm chaser in the area only reported funnel cloud.

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. One was issued for the county at another hour that day.

The county was under a severe thunderstorm watch, issued at 20:26 UTC and running to 03:00 UTC.

Issued (UTC)ExpiredProductOffice
20:26 UTC03:00 UTCSevere Thunderstorm WatchCYS
00:03 UTC01:00 UTCSevere Thunderstorm WarningCYS
00:55 UTC01:30 UTCTornado WarningCYS
01:32 UTC01:46 UTCTornado WarningCYS
01:53 UTC02:21 UTCTornado WarningCYS

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 20:38 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.

Rapid City, SD (KUNR), 00:00Z

0.6 hours before the tornado, 171 km from the path. May 10, 2011.

Skew-T log-pSkew-T log-p diagram, Rapid City, SD at 00:00Z on 2011-05-10Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 231 joules per kilogram, CIN -129, lifted condensation level 581 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, Rapid City, SD at 00:00Z on 2011-05-10The 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 114 square meters per square second, 0 to 6 km bulk shear 46 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
231 J/kg
Mixed-layer CIN
-129 J/kg
Surface CAPE
550 J/kg
Mixed-layer LCL
581 m above ground
0-6 km bulk shear
46 kt
0-1 km bulk shear
14 kt
0-1 km storm-relative helicity
114 m²/s²
0-3 km storm-relative helicity
247 m²/s²
Significant tornado parameter
-0.0
Supercell composite
-0.0
0-3 km lapse rate
4.7 K/km

Open this sounding in Storm Lab

Rapid City, SD (KUNR), 12:00Z

11.4 hours after it, 171 km from the path. May 10, 2011.

Skew-T log-pSkew-T log-p diagram, Rapid City, SD at 12:00Z on 2011-05-10Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 17 joules per kilogram, CIN -88, lifted condensation level 1211 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, Rapid City, SD at 12:00Z on 2011-05-10The 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 -5 square meters per square second, 0 to 6 km bulk shear 82 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
17 J/kg
Mixed-layer CIN
-88 J/kg
Surface CAPE
1 J/kg
Mixed-layer LCL
1211 m above ground
0-6 km bulk shear
82 kt
0-1 km bulk shear
13 kt
0-1 km storm-relative helicity
-5 m²/s²
0-3 km storm-relative helicity
92 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.2 K/km

Open this sounding in Storm Lab

The radar

The Rapid City radar (KUDX), 178 km away, was scanning. The volume nearest the touchdown began at 00:36 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
00:37 UTCHAIL 15 E HarrisonSioux, NE
00:37 UTCHAIL 1.51 Ssw HarrisonSioux, NE
01:10 UTCFUNNEL CLOUD5 E WhitneyDawes, NEA FUNNEL CLOUD WAS REPORTED JUST NORTH OF HIGHWAY 20...4 TO 5 MILES EAST OF WHITNEY.
01:10 UTCTORNADO10 E HarrisonSioux, NE911 CALL FROM THE PUBLIC REPORTED A TORNADO ON THE GROUND 10 MILES EAST OF HARRISON
01:11 UTCHAIL 117 E HarrisonSioux, NEHAIL FALLING AS WE SPOKE.
01:18 UTCHAIL 0.2510 Nw CrawfordSioux, NE
01:18 UTCHAIL 0.25CrawfordDawes, NE
01:30 UTCHAIL 1.7511 N CrawfordDawes, NE
01:57 UTCHAIL 0.2512 Nw ChadronDawes, NECOVERS THE GROUND.
02:05 UTCHAIL 0.514 Sse CrawfordDawes, NE
02:09 UTCHAIL 1.7510 Nw HemingfordBox Butte, NEHAIL WAS 2 MILES SOUTH OF MARSLAND ALONG HWY 2.
02:09 UTCHAIL 1.7515 Nw HemingfordDawes, NEHAIL WAS 2 MILES SOUTH OF MARSLAND ALONG HWY 2.

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 NebraskaEvery tornado in Nebraska since 1950Warnings in force in Nebraska nowThe forecast where you are

The other tornadoes of May 9, 2011

4 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 97:10 PM MDTEF0Sioux, NE0.020
May 98:55 PM MDTEF1Haakon, SD2.530$5,000
May 99:45 PM MDTEF0Haakon, SD0.020$5,000
May 911:07 PM MDTEF0Pennington, SD1.530$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.