Tornadoes · United States · Wyoming · 2015

EF0 tornado, Bosler to Cooper Lake, Wyoming, May 23, 2015

From Bosler to Cooper Lake, this EF0 tornado ran 0.3 miles across Albany County on May 23, 2015, touching down at 12:55 PM MDT and reaching 35 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 23, 2015
Touchdown
12:55 PM MDT (18:55 UTC)
Lifted
1:00 PM MDT (19:00 UTC)
On the ground
5 minutes
Path length
0.3 miles (0.5 km)
Path width
35 yards (32 m)
Deaths
0
Injuries
0
County
Albany County
Touchdown point
41.536, -105.843
Lift-off point
41.539, -105.847
Record number
1505231255-01

What the Weather Service recorded

Afternoon thunderstorms over southeast Wyoming produced heavy rain and a weak tornado.

A weak tornado touched down in open country eight miles west-northwest of Bosler and moved northwest at 15 mph. The tornado was on the ground for five minutes then dissipated. No damage was reported.

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.

Issued (UTC)ExpiredProductOffice
19:08 UTC19:45 UTCTornado WarningCYS
23:24 UTC11:15 UTCFlood 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 General Thunderstorms Risk. The outlook in force was issued at 16:30 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.

Riverton, WY (KRIW), 12:00Z

6.9 hours before the tornado, 271 km from the path. May 23, 2015.

Skew-T log-pSkew-T log-p diagram, Riverton, WY at 12:00Z on 2015-05-23Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 0 joules per kilogram, CIN -94161, lifted condensation level 824 meters above ground. Wind barbs in knots down the right edge.LCL10008507005003002001001 km2 km3 km6 km9 km12 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, Riverton, WY at 12:00Z on 2015-05-23The 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 -53 square meters per square second, 0 to 6 km bulk shear 17 knots.1939Sfc1 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
0 J/kg
Mixed-layer CIN
-94161 J/kg
Surface CAPE
254 J/kg
Mixed-layer LCL
824 m above ground
0-6 km bulk shear
17 kt
0-1 km bulk shear
14 kt
0-1 km storm-relative helicity
-53 m²/s²
0-3 km storm-relative helicity
-15 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.9 K/km

Open this sounding in Storm Lab

Riverton, WY (KRIW), 00:00Z

5.1 hours after it, 271 km from the path. May 24, 2015.

Skew-T log-pSkew-T log-p diagram, Riverton, WY at 00:00Z on 2015-05-24Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 0 joules per kilogram, CIN -788, lifted condensation level 1213 meters above ground. Wind barbs in knots down the right edge.LCL10008507005003002001001 km2 km3 km6 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, Riverton, WY at 00:00Z on 2015-05-24The 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 -20 square meters per square second, 0 to 6 km bulk shear 9 knots.1939Sfc1 km3 km6 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
0 J/kg
Mixed-layer CIN
-788 J/kg
Surface CAPE
266 J/kg
Mixed-layer LCL
1213 m above ground
0-6 km bulk shear
9 kt
0-1 km bulk shear
13 kt
0-1 km storm-relative helicity
-20 m²/s²
0-3 km storm-relative helicity
20 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
6.5 K/km

Open this sounding in Storm Lab

The surface observations

Laramie/Gen. Brees (LAR), 29 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
17:53 UTC5442150° 18 kt1014.9
18:53 UTC5039150° 19 kt1015.6
19:53 UTC5141180° 15 kt1015.6
20:53 UTC5541110° 9 kt1014.2

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

The radar

The Cheyenne radar (KCYS), 97 km away, was scanning. The volume nearest the touchdown began at 18:54 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
18:55 UTCTORNADO8 Wsw BoslerAlbany, WYRECEIVED REPORTS OF A TORADO.

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

This ground now

The live radar over the trackEvery 2015 tornado in WyomingEvery tornado in Wyoming since 1950Warnings in force in Wyoming nowThe forecast where you are

The other tornadoes of May 23, 2015

21 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 235:12 PM CDTEF1Grady, OK6.0500
May 235:59 PM CDTEF0Murray, OK3.040
May 236:05 PM CDTEF0Pontotoc, OK0.220
May 236:10 PM CDTEF0Murray, OK0.550
May 236:11 PM CDTEF1McClain, OK2.050
May 236:16 PM CDTEF0Garvin, OK0.250
May 236:25 PM CDTEF1Pontotoc, OK3.8100
May 236:30 PM CDTEF0McClain, OK0.550
May 237:05 PM CDTEF1Garvin, OK0.550
May 237:13 PM CDTEF0Hughes, OK0.250
May 238:16 PM CDTEF1Bexar, TX0.4150
May 238:44 PM CDTEF0Latimer, OK1.675
May 238:53 PM CDTEF0Hays, TX5.7100
May 238:58 PM CDTEF1Travis, TX1.3200
May 239:11 PM CDTEF0Travis, TX2.5200
May 239:22 PM CDTEF1Williamson, TX3.1200
May 239:37 PM CDTEF0Travis, TX1.2125
May 239:39 PM CDTEF1Travis, TX0.6250
May 239:43 PM CDTEF1Bastrop, TX0.8200
May 239:47 PM CDTEF0Williamson, TX0.350
May 239:47 PM CDTEF1Williamson, TX0.6150

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.