F0 tornado, Sun Prairie to Tampico, Montana, July 20, 2001

1. F040 to 72 mphthis tornado

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

2. F173 to 112 mph

   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

F0

Date

July 20, 2001

Touchdown

3:20 PM MDT (21:20 UTC)

Path length

29.0 miles (46.7 km)

Path width

100 yards (91 m)

Deaths

0

Injuries

0

Counties

Phillips and Valley counties

Touchdown point

47.880, -107.650

Lift-off point

48.020, -107.100

Record number

1074

A large supercell formed in Southwestern Phillips County and headed east across southern Valley County. The storm produced a tornado that crossed from Phillips County into Valley County. The tornado dissipated as the storm moved east, but golfball size hail was reported for 20 minutes at The Pines Recreation Area. The storm crossed over the east side of Ft. Peck Lake and formed another tornado near the Rock Creek Recreation area. The tornado then crossed Highway 24, in McCone County. Four inch diameter hail was reported with this storm at the time of the tornado. The tornado continued in a southeast path towards the town of Circle. The last known location of the tornado before it dissipated was 22 miles northwest of Circle. Downburst winds and golfball size hail then became the more significant threat from this storm. The hail and high winds caused a large area of 100 percent crop damage from 10 miles north and northwest of Circle to Lindsay. The damage swath was 1 to 5 miles wide. Other large hail and high wind reports were received from the Richey and Bloomfield areas in northwestern Dawson County as well. 25 large steel electrical towers were blown over in the area between Circle and Richey, and 25 wooden electrical poles were snapped also. The storm continued southeast toward Glendive and then followed Interstate 94 into North Dakota. No more substantial damage was reported once the storm passed through the Lindsay area. A few smaller tornados were reported by law enforcement officials northwest and north of the Glendive area, but they did not cause any damage and were short lived.

A tornado developed 11 miles east of Sun Prairie and moved into Valley County. The tornado moved through open prairie and caused no damage.

A tornado moved into Southwest Valley County and moved east before dissipating. It moved through open prairie and caused no damage. The storm and wall cloud were seen from the National Weather Service office over 35 miles away.

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

31 minutes of warning. NWS GGW issued a tornado warning for this county at 20:49 UTC, 31 minutes before the tornado touched down, in force until 21:45 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 Moderate Risk. The outlook in force was issued at 19:36 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.

The Glasgow radar (KGGW), 63 km away, was scanning. The volume nearest the touchdown began at 21:20 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.

The live radar over the trackEvery 2001 tornado in MontanaEvery tornado in Montana since 1950Warnings in force in Montana nowThe forecast where you are

6 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.