EF1 tornado, Opheim, Montana, August 10, 2007

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.

Rating

EF1

Date

August 10, 2007

Touchdown

7:45 PM MDT (01:45 UTC)

Lifted

7:53 PM MDT (01:53 UTC)

On the ground

8 minutes

Path length

0.3 miles (0.4 km)

Path width

10 yards (9 m)

Deaths

0

Injuries

0

Property damage

$10,000

County

Valley County

Touchdown point

48.783, -106.442

Lift-off point

48.783, -106.442

Record number

0708101945-01

A vigorous upper level storm system and strong cold front produced a widespread severe weather outbreak in northeastern Montana. The majority of the events were high wind, a few reports of large hail, and two tornadoes.

A fully loaded grain truck weighing 40,000 to 45,000 pounds was in the path of this tornado. A bolted down upper portion of the truck's grain bin, which weighed 400 pounds, was lifted straight into the air causing minimal damage to the rest of the truck bin. It then spun overhead and slammed into the ground twice at a distance of about 80 feet from the vehicle. A witness reported a rotating wall cloud and a rain wrapped tornado. A damage survey was conducted by the NWS and the tornado was rated in the low EF1 range.

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

19 minutes of warning. NWS GGW issued a tornado warning for this county at 01:26 UTC, 19 minutes before the tornado touched down, in force until 02:00 UTC.

The county was under a severe thunderstorm watch, issued at 22:45 UTC and running to 04:44 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 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 00:41 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), 66 km away, was scanning. The volume nearest the touchdown began at 01:45 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 2007 tornado in MontanaEvery tornado in Montana since 1950Warnings in force in Montana nowThe forecast where you are

7 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.