F1 tornado, Ft Lupton to Platteville, Colorado, August 10, 1999

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.

Rating

F1

Date

August 10, 1999

Touchdown

4:55 PM MDT (22:55 UTC)

Path length

0.1 miles (0.2 km)

Path width

0 yards (0 m)

Deaths

0

Injuries

0

County

Weld County

Touchdown point

40.220, -104.820

Lift-off point

40.220, -104.820

Record number

191

Thunderstorms producing tornadoes, damaging straight-line winds, heavy rain and hail hammered portions of the Urban Corridor and Northeast Plains. In Denver, heavy rain and small hail, up to 2.5 inches in an hour, caused a 20-ft by 50-ft section of roof to collapse at a furniture warehouse. Damage to the warehouse was estimated at $1.0 million. Heavy rain also flooded several underpasses with up to 3 feet of water, which resulted in a number of stalled vehicles. Damaging straight-line winds along with several tornadoes were reported across Weld and Morgan Counties. In Fort Lupton, officials believed a tornado bounced from southwest to northeast across the area. Spotty damage was reported along a 5-mile path as trees, power poles and lines were downed. In addition, an empty semi-trailer was overturned onto another vehicle northeast of town. Another tornado touched down briefly in Platteville where a tree fell onto a house. Strong thunderstorm winds also blew a pickup truck off of Interstate 76 near Fort Morgan.Heavy rain and large hail caused flooding and flash flooding problems in parts of Logan and Phillips Counties. Storm totals ranged from 3 to 6 inches southeast of Haxtun, near the Yuma county line. Several county roads were washed out with widespread field flooding reported. Heavy rain and hail also stripped corn and sunflower crops in the area.

See narrative below.

A small tornado touched down, but did no damage.

A small tornado touched down, downing some power lines as well a tree, which fell onto a house.

See the narrative below.

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

9 minutes of warning. NWS BOU issued a tornado warning for this county at 22:46 UTC, 9 minutes before the tornado touched down, in force until 23:15 UTC.

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 Storm Prediction Center had this point in a Slight Risk. The outlook in force was issued at 21:40 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 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.

Greeley/Weld (Awos) (GXY), 29 km from the path, in the two hours either side.

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

The live radar over the trackEvery 1999 tornado in ColoradoEvery tornado in Colorado since 1950Warnings in force in Colorado nowThe forecast where you are

4 more were confirmed in the United States that day.

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.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.