Tornadoes · United States · Colorado · 2017

EF0 tornado, Anton to Arickaree, Colorado, August 12, 2017

From Anton to Arickaree, this EF0 tornado ran 0.0 miles across Washington County on August 12, 2017, touching down at 5:45 PM MDT and reaching 25 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
August 12, 2017
Touchdown
5:45 PM MDT (23:45 UTC)
Path length
0.0 miles (0.0 km)
Path width
25 yards (23 m)
Deaths
0
Injuries
0
County
Washington County
Touchdown point
39.680, -103.130
Lift-off point
39.680, -103.130
Record number
1708121745-01

What the Weather Service recorded

Severe thunderstorm broke out along a boundary in Washington County. The severe thunderstorms produced large hail, from 1 to 2 inches in diameter. Four landspouts developed briefly along the boundary but did no damage.

A tornado briefly touched down in open country.

A tornado briefly touched down in open country.

A tornado briefly touched down in open country.

A tornado briefly touched down in open country.

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

The warnings

15 minutes of warning. NWS BOU issued a tornado warning for this county at 23:30 UTC, 15 minutes before the tornado touched down, in force until 00:00 UTC.

The county was under a severe thunderstorm watch, issued at 21:16 UTC and running to 00:48 UTC.

Issued (UTC)ExpiredProductOffice
21:16 UTC00:48 UTCSevere Thunderstorm WatchBOU
22:33 UTC23:15 UTCSevere Thunderstorm WarningBOU
22:54 UTC23:45 UTCSevere Thunderstorm WarningBOU
23:30 UTC00:00 UTCTornado WarningBOU
23:38 UTC00:01 UTCSevere Thunderstorm WarningBOU
23:52 UTC03:45 UTCFlood AdvisoryBOU

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. 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.

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.

Denver, CO (KDEN), 12:00Z

11.8 hours before the tornado, 23 km from the path. August 12, 2017.

Skew-T log-pSkew-T log-p diagram, Denver, CO at 12:00Z on 2017-08-12Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 166 joules per kilogram, CIN -274, lifted condensation level 1194 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, Denver, CO at 12:00Z on 2017-08-12The 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 30 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
166 J/kg
Mixed-layer CIN
-274 J/kg
Surface CAPE
287 J/kg
Mixed-layer LCL
1194 m above ground
0-6 km bulk shear
30 kt
0-1 km bulk shear
12 kt
0-1 km storm-relative helicity
53 m²/s²
0-3 km storm-relative helicity
46 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.0 K/km

Open this sounding in Storm Lab

Denver, CO (KDEN), 00:00Z

0.2 hours after it, 23 km from the path. August 13, 2017.

Skew-T log-pSkew-T log-p diagram, Denver, CO at 00:00Z on 2017-08-13Temperature 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 -66224, lifted condensation level 2378 meters above ground. Wind barbs in knots down the right edge.LCL10008507005003002001001 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, Denver, CO at 00:00Z on 2017-08-13The 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 120 square meters per square second, 0 to 6 km bulk shear 28 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
0 J/kg
Mixed-layer CIN
-66224 J/kg
Surface CAPE
513 J/kg
Mixed-layer LCL
2378 m above ground
0-6 km bulk shear
28 kt
0-1 km bulk shear
22 kt
0-1 km storm-relative helicity
120 m²/s²
0-3 km storm-relative helicity
194 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
6.9 K/km

Open this sounding in Storm Lab

The radar

The Denver radar (KFTG), 122 km away, was scanning. The volume nearest the touchdown began at 23:46 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
22:42 UTCHAIL 2PlatnerWashington, CO
23:10 UTCTORNADO7 Wnw Arickaree SchoolWashington, COBRIEF LAND SPOT
23:26 UTCTSTM WND GST 505 Ese ElbaWashington, COALONG WITH NICKEL SIZE HAIL AND HEAVY RAIN
23:27 UTCTORNADO1 Nw Arickaree SchoolWashington, CO
23:30 UTCTORNADO5 Se AntonWashington, CO
23:30 UTCTORNADOSe AntonWashington, CO
23:40 UTCHAIL 11 Sse Arickaree SchoolWashington, CO
23:42 UTCHAIL 1.53 S Arickaree SchoolWashington, CO
23:45 UTCTORNADO7 Se AntonWashington, CO

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

This ground now

The live radar over the trackEvery 2017 tornado in ColoradoEvery tornado in Colorado since 1950Warnings in force in Colorado nowThe forecast where you are

The other tornadoes of August 12, 2017

4 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 123:12 PM EDTEF1Juniata, PA5.5200$500,000
August 125:10 PM MDTEF0Washington, CO0.025
August 125:27 PM MDTEF0Washington, CO0.025
August 125:30 PM MDTEF0Washington, CO0.025

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.