Tornadoes · United States · Colorado · 2015

EF1 tornado, Deckers, Colorado, July 21, 2015

This EF1 tornado ran 0.3 miles across Douglas County on July 21, 2015, touching down at 2:05 PM MDT and reaching 100 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 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 21, 2015
Touchdown
2:05 PM MDT (20:05 UTC)
Lifted
2:08 PM MDT (20:08 UTC)
On the ground
3 minutes
Path length
0.3 miles (0.5 km)
Path width
100 yards (91 m)
Deaths
0
Injuries
0
County
Douglas County
Touchdown point
39.268, -105.106
Lift-off point
39.269, -105.100
Record number
1507211405-01

The damage survey

4 damage points were recorded along this path by NWS BOU, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 90 mph.

Survey points are preliminary and are the raw material the published rating was built from. Source: NWS Damage Assessment Toolkit.

What the Weather Service recorded

A tornado touched down at damaged in Pike National Forest, southwest of Denver. In addition, a wet microburst produced intense winds to 70 mph and brief heavy rain, over one inch in 20 minutes.

A tornado touched down and damaged the Devil's Head campground and picnic grounds in Pike National Forest as well as the trail to the Fire Lookout Tower. Six acres of aspen, spruce and fir trees were knocked down. The tornado touched down at an elevation of 9,700 feet.

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
19:45 UTC20:24 UTCFlood AdvisoryBOU
21:37 UTC23:01 UTCFlash Flood WarningBOU
22:21 UTC00:30 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 Marginal Risk. The outlook in force was issued at 19:48 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

8.1 hours before the tornado, 174 km from the path. July 21, 2015.

Skew-T log-pSkew-T log-p diagram, Denver, CO at 12:00Z on 2015-07-21Temperature 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 -79448, lifted condensation level 1832 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 12:00Z on 2015-07-21The 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 52 square meters per square second, 0 to 6 km bulk shear 26 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
-79448 J/kg
Surface CAPE
36 J/kg
Mixed-layer LCL
1832 m above ground
0-6 km bulk shear
26 kt
0-1 km bulk shear
22 kt
0-1 km storm-relative helicity
52 m²/s²
0-3 km storm-relative helicity
154 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.8 K/km

Open this sounding in Storm Lab

Denver, CO (KDEN), 00:00Z

3.9 hours after it, 174 km from the path. July 22, 2015.

Skew-T log-pSkew-T log-p diagram, Denver, CO at 00:00Z on 2015-07-22Temperature 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 -75018, lifted condensation level 2011 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 2015-07-22The 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 -37 square meters per square second, 0 to 6 km bulk shear 34 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
-75018 J/kg
Surface CAPE
923 J/kg
Mixed-layer LCL
2011 m above ground
0-6 km bulk shear
34 kt
0-1 km bulk shear
9 kt
0-1 km storm-relative helicity
-37 m²/s²
0-3 km storm-relative helicity
-31 m²/s²
Significant tornado parameter
0.0
Supercell composite
-0.1
0-3 km lapse rate
8.1 K/km

Open this sounding in Storm Lab

The surface observations

Denver/Centennial (APA), 40 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
18:53 UTC7756170° 9 kt1018.3
19:28 UTC7856170° 17 kt1017.6TS
19:53 UTC7357230° 11 kt1018.3TS
20:23 UTC6758300° 9 kt1018.3
20:25 UTC6857280° 9 kt1018.3TS
20:53 UTC6760270° 13 kt1018.3-TSRA
21:14 UTC6860290° 5 kt1017.6
21:53 UTC7158290° 8 kt1016.9

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

The radar

The Denver radar (KFTG), 75 km away, was scanning. The volume nearest the touchdown began at 20:03 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
20:45 UTCHEAVY RAIN 1.054 Nnw LarkspurDouglas, COIN 30 MINUTES
22:01 UTCHEAVY RAIN 12 Nne MonumentEl Paso, CO1 OF RAINFALL OBSERVED
22:01 UTCHEAVY RAIN 12 Nne MonumentEl Paso, CO
22:12 UTCHEAVY RAIN 2.754 E MonumentEl Paso, CO2.75 INCHES OF RAIN IN 1 HOUR.
22:25 UTCHEAVY RAIN 0.714 Ene Air Force AcademyEl Paso, COIN THE PAST 20 MINUTES. SMALL PEA SIZED HAIL.
22:25 UTCHEAVY RAIN 1.36 Ene MonumentEl Paso, COFELL IN 40 MINUTES
22:42 UTCHAIL 0.882 Sse Black ForestEl Paso, CO
22:42 UTCHEAVY RAIN 0.882 Sse Black ForestEl Paso, COIN 10 MINUTES

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 ColoradoEvery tornado in Colorado since 1950Warnings in force in Colorado 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.