F1 tornado, Hamilton to Dulles Intl Arpt, Virginia, September 17, 2004

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

September 17, 2004

Touchdown

5:20 PM EDT (21:20 UTC)

Path length

12.0 miles (19.3 km)

Path width

200 yards (183 m)

Deaths

0

Injuries

0

Property damage

$500,000

County

Loudoun County

Touchdown point

39.080, -77.650

Lift-off point

39.270, -77.630

Record number

1753

A tornado touched down in western Loudoun County. This storm was a continuation of a track of the storm that moved through Fauquier County Virginia. The storm first touched down south of Hamilton and, intermittent damage was noted from Hamilton to Lovettsville. A farm near Hamilton suffered severe damage. The farmhouse, horse barn and outbuildings were severely damaged or demolished. Two thoroughbred horses were cut by flying debris. The tornado produced damage along a 12 mile track. This storm continued to travel north into Maryland and produced damage in extreme southwest Frederick and eastern Washington Counties.

A thunderstorm moved into eastern Loudoun County from Fairfax County near the Dulles International Airport. The storm produced a tornado which touched down at Dulles International Airport and passed within one half mile of the National Weather Service Forecast Office in Sterling. This prompted the staff on duty to seek shelter in the office constructed saferoom. As the storm traveled north from the Dulles International Airport, it produced minor tree damage. More extensive damage occurred north of Waxpool Road at the Beaumede Corporate Park. Seven buildings were damaged. A wall collapsed in one of the buildings. A tractor trailer was overturned. The tornado also pushed two cars into the side of a building. The tornado weakened as it traveled north. The last damage in Loudoun County was reported just north of Route 7.

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

22 minutes of warning. NWS LWX issued a tornado warning for this county at 20:58 UTC, 22 minutes before the tornado touched down, in force until 22:00 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, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:53 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.

Leesburg/Godfrey (JYO), 13 km from the path, in the two hours either side.

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

The Sterling radar (KLWX), 26 km away, was scanning. The volume nearest the touchdown began at 21:21 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.

Local storm reports within 60 km of the path, in the three hours either side.

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

The live radar over the trackEvery 2004 tornado in VirginiaEvery tornado in Virginia since 1950Warnings in force in Virginia nowThe forecast where you are

57 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.