Tornadoes · United States · Oklahoma · 2011

EF1 tornado, Murphy to Locust Grove, Oklahoma, May 20, 2011

From Murphy to Locust Grove, this EF1 tornado ran 1.5 miles across Mayes County on May 20, 2011, touching down at 9:37 AM CDT and reaching 100 yards wide. It killed nobody, and did $35,000 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
May 20, 2011
Touchdown
9:37 AM CDT (14:37 UTC)
Lifted
9:38 AM CDT (14:38 UTC)
On the ground
1 minutes
Path length
1.5 miles (2.4 km)
Path width
100 yards (91 m)
Deaths
0
Injuries
0
Property damage
$35,000
County
Mayes County
Touchdown point
36.098, -95.141
Lift-off point
36.112, -95.122
Record number
1105200837-01

What the Weather Service recorded

Thunderstorms developed into eastern Oklahoma during the early morning hours of the 20th ahead of an upper level disturbance and associated cold front. An isolated tornado developed in Mayes County from an intense storm.

A tornado damaged metal buildings, uprooted several metal fence posts, snapped a large hardwood tree, snapped numerous large tree limbs, and destroyed a storage shed. Maximum estimated wind in the tornado based on this damage was about 90 mph.

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.

Issued (UTC)ExpiredProductOffice
14:45 UTC16:45 UTCFlood AdvisoryTSA
16:12 UTC02:22 UTCFlash Flood WatchTSA

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 12:54 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.

Springfield, MO (KSGF), 12:00Z

2.6 hours before the tornado, 148 km from the path. May 20, 2011.

Skew-T log-pSkew-T log-p diagram, Springfield, MO at 12:00Z on 2011-05-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 537 joules per kilogram, CIN -280, lifted condensation level 940 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, Springfield, MO at 12:00Z on 2011-05-20The 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 222 square meters per square second, 0 to 6 km bulk shear 33 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
537 J/kg
Mixed-layer CIN
-280 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
940 m above ground
0-6 km bulk shear
33 kt
0-1 km bulk shear
29 kt
0-1 km storm-relative helicity
222 m²/s²
0-3 km storm-relative helicity
161 m²/s²
Significant tornado parameter
0.0
Supercell composite
1.6
0-3 km lapse rate
3.3 K/km

Open this sounding in Storm Lab

Springfield, MO (KSGF), 00:00Z

9.4 hours after it, 148 km from the path. May 21, 2011.

Skew-T log-pSkew-T log-p diagram, Springfield, MO at 00:00Z on 2011-05-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 41 joules per kilogram, CIN -326, lifted condensation level 1655 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, Springfield, MO at 00:00Z on 2011-05-21The 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 228 square meters per square second, 0 to 6 km bulk shear 35 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
41 J/kg
Mixed-layer CIN
-326 J/kg
Surface CAPE
140 J/kg
Mixed-layer LCL
1655 m above ground
0-6 km bulk shear
35 kt
0-1 km bulk shear
21 kt
0-1 km storm-relative helicity
228 m²/s²
0-3 km storm-relative helicity
250 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
4.4 K/km

Open this sounding in Storm Lab

The surface observations

Tahlequah Municipal (TQH), 23 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
12:55 UTC6868130° 9 kt1009.1
13:15 UTC6868130° 7 kt1009.5
13:35 UTC6868150° 9 kt161009.5BR
13:55 UTC6868140° 7 kt1009.1
14:15 UTC6868140° 10 kt151008.8
14:35 UTC6868140° 9 kt151009.5BR
14:55 UTC6868150° 5 kt1009.8
15:15 UTC66.264.4270° 14 kt191011.2BR
15:35 UTC62.662.6280° 4 kt1010.8BR
15:55 UTC62.662.6 1011.5BR
16:15 UTC62.662.6 1010.8BR
16:35 UTC62.662.6130° 4 kt1011.5BR

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

The radar

The Tulsa radar (KINX), 40 km away, was scanning. The volume nearest the touchdown began at 14:38 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
14:37 UTCTORNADO7 S Locust GroveMayes, OKA TORNADO DAMAGED METAL BUILDINGS...UPROOTED SEVERAL METAL FENCE POSTS...SNAPPED A LARGE HARDWOOD TREE...SNAPPED NUMEROUS LARGE LIMBS...AND DESTROYED A STORAGE SHED. RATING WAS EF-1. PATH LENGTH WAS ABOUT 1.5 MILES. MAXI
14:38 UTCTSTM WND DMG6 Sse Locust GroveMayes, OKBUILDING AND TREE DAMAGE REPORTED ON STATE HIGHWAY 82 ON THE CHEROKEE AND MAYES COUNTY LINE.

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 OklahomaEvery tornado in Oklahoma since 1950Warnings in force in Oklahoma nowThe forecast where you are

The other tornadoes of May 20, 2011

5 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 208:20 AM CDTEF0Washington, AR0.550$1,000
May 205:36 PM CDTEF0Red River, TX1.650
May 205:48 PM CDTEF0Hot Spring, AR3.1100$25,000
May 206:38 PM CDTEF0Harrison, TX6.850
May 208:27 PM MDTEF1Prairie, MT0.166$75,000

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.