Tornadoes · United States · Colorado · 1986

F1 tornado, Weld County, Colorado, August 2, 1986

This F1 tornado ran 0.7 miles across Weld County on August 2, 1986, touching down at 10:50 PM MDT and reaching 30 yards wide. It killed nobody, and did $500 to $5,000 of property damage.

The rating scale

Tracks are drawn in the color of the rating. The Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

  1. F040 to 72 mph

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

  2. F173 to 112 mphthis tornado

    Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

  3. F2113 to 157 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. F3158 to 206 mph

    Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

  5. F4207 to 260 mph

    Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

  6. F5261 to 318 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
F1
Date
August 2, 1986
Touchdown
10:50 PM MDT (04:50 UTC)
Path length
0.7 miles (1.1 km)
Path width
30 yards (27 m)
Deaths
0
Injuries
0
Property damage
$500 to $5,000
County
Weld County
Touchdown point
40.580, -104.250
Record number
595

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
22:49 UTC23:45 UTCSevere Thunderstorm WarningBOU
23:27 UTC00:30 UTCSevere Thunderstorm WarningBOU
01:06 UTC02:00 UTCSevere Thunderstorm WarningBOU
02:20 UTC03:15 UTCSevere Thunderstorm WarningBOU
03:23 UTC04:15 UTCSevere Thunderstorm WarningBOU

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 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), 00:00Z

4.8 hours before the tornado, 117 km from the path. August 3, 1986.

Skew-T log-pSkew-T log-p diagram, Denver, CO at 00:00Z on 1986-08-03Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1026 joules per kilogram, CIN -10, lifted condensation level 2147 meters above ground. Wind barbs in knots down the right edge.LCLEL10008507005003002001001 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, Denver, CO at 00:00Z on 1986-08-03The 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 -14 square meters per square second, 0 to 6 km bulk shear 28 knots.193958Sfc1 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
1026 J/kg
Mixed-layer CIN
-10 J/kg
Surface CAPE
1314 J/kg
Mixed-layer LCL
2147 m above ground
0-6 km bulk shear
28 kt
0-1 km bulk shear
4 kt
0-1 km storm-relative helicity
-14 m²/s²
0-3 km storm-relative helicity
19 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.3
0-3 km lapse rate
9.0 K/km

Open this sounding in Storm Lab

Denver, CO (KDEN), 12:00Z

7.2 hours after it, 117 km from the path. August 3, 1986.

Skew-T log-pSkew-T log-p diagram, Denver, CO at 12:00Z on 1986-08-03Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 440 joules per kilogram, CIN -303, lifted condensation level 1851 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 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, Denver, CO at 12:00Z on 1986-08-03The 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 109 square meters per square second, 0 to 6 km bulk shear 46 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
440 J/kg
Mixed-layer CIN
-303 J/kg
Surface CAPE
106 J/kg
Mixed-layer LCL
1851 m above ground
0-6 km bulk shear
46 kt
0-1 km bulk shear
13 kt
0-1 km storm-relative helicity
109 m²/s²
0-3 km storm-relative helicity
115 m²/s²
Significant tornado parameter
0.0
Supercell composite
-0.3
0-3 km lapse rate
5.9 K/km

Open this sounding in Storm Lab

This ground now

The live radar over the trackEvery 1986 tornado in ColoradoEvery tornado in Colorado since 1950Warnings in force in Colorado nowThe forecast where you are

The other tornadoes of August 2, 1986

5 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 21:30 PM EDTF1Clarke, VA2.050
August 22:25 PM EDTF1Macomb, MI0.723
August 22:40 PM EDTF1Wayne, MI0.3203
August 24:30 PM CDTF0Cimarron, OK0.550
August 29:30 PM CDTF1Castro, TX0.240$50,000 to $500,000

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.