Tornadoes · United States · Idaho · 1991
F1 tornado, Jefferson County, Idaho, June 4, 1991
This F1 tornado ran 0.2 miles across Jefferson County on June 4, 1991, touching down at 8:00 PM MDT and reaching 30 yards wide. It killed nobody, and did $5,000 to $50,000 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.
F040 to 72 mph
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
F173 to 112 mphthis tornado
Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.
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.
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.
F4207 to 260 mph
Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.
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.
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
- June 4, 1991
- Touchdown
- 8:00 PM MDT (02:00 UTC)
- Path length
- 0.2 miles (0.3 km)
- Path width
- 30 yards (27 m)
- Deaths
- 0
- Injuries
- 0
- Property damage
- $5,000 to $50,000
- County
- Jefferson County
- Touchdown point
- 43.630, -111.780
- Record number
- 772
The warnings
No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.
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 forecast that day
The Storm Prediction Center had this point in a General Thunderstorms Risk. The outlook in force was issued at 06:26 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 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.
Lander/Hunt Fiel, WY (KLND), 00:00Z
2.0 hours before the tornado, 265 km from the path. June 5, 1991.
- Mixed-layer CAPE
- 40 J/kg
- Mixed-layer CIN
- -62 J/kg
- Surface CAPE
- 926 J/kg
- Mixed-layer LCL
- 2132 m above ground
- 0-6 km bulk shear
- 22 kt
- 0-1 km bulk shear
- 2 kt
- 0-1 km storm-relative helicity
- 14 m²/s²
- 0-3 km storm-relative helicity
- 85 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
- 0-3 km lapse rate
- 9.3 K/km
Lander/Hunt Fiel, WY (KLND), 12:00Z
10.0 hours after it, 265 km from the path. June 5, 1991.
- Mixed-layer CAPE
- 6 J/kg
- Mixed-layer CIN
- -107 J/kg
- Surface CAPE
- 0 J/kg
- Mixed-layer LCL
- 833 m above ground
- 0-6 km bulk shear
- 17 kt
- 0-1 km bulk shear
- 8 kt
- 0-1 km storm-relative helicity
- 47 m²/s²
- 0-3 km storm-relative helicity
- 56 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
- 0-3 km lapse rate
- 5.1 K/km
The surface observations
Idaho Falls/Fanning (IDA), 27 km from the path, in the two hours either side.
| Time (UTC) | Temp (°F) | Dew point (°F) | Wind | Gust (kt) | Pressure (mb) | Weather |
|---|---|---|---|---|---|---|
| 00:00 UTC | 68 | 56 | 360° 12 kt | 1010.5 | ||
| 01:00 UTC | 66 | 57 | 260° 19 kt | 39 | 1010.5 | TSRA |
| 01:01 UTC | 260° 17 kt | 1010.8 | TSRA | |||
| 01:16 UTC | 310° 7 kt | 1011.2 | TS | |||
| 02:00 UTC | 58 | 52 | 240° 5 kt | 1012.2 | ||
| 03:00 UTC | 58 | 53 | 90° 10 kt | 1012.2 |
From the Iowa Environmental Mesonet's archive of airport observations.
This ground now
The live radar over the trackEvery 1991 tornado in IdahoEvery tornado in Idaho since 1950Warnings in force in Idaho nowThe forecast where you are
The other tornadoes of June 4, 1991
8 more were confirmed in the United States that day.
| Date | Time | Rating | Where | Path (mi) | Width (yd) | Deaths | Injuries | Damage |
|---|---|---|---|---|---|---|---|---|
| June 4 | 3:15 PM CDT | F0 | Madison, NE | 0.1 | 10 | |||
| June 4 | 3:45 PM CDT | F2 | Madison, NE | 3.0 | 100 | $50,000 to $500,000 | ||
| June 4 | 4:36 PM CDT | F0 | Stanton, NE | 0.1 | 10 | |||
| June 4 | 5:00 PM CDT | F1 | Stanton, NE | 0.1 | 20 | |||
| June 4 | 5:30 PM CDT | F1 | Stanton, NE | 2.5 | 73 | $500 to $5,000 | ||
| June 4 | 6:00 PM CDT | F0 | Colfax, NE | 0.1 | 10 | $500 to $5,000 | ||
| June 4 | 6:15 PM CDT | F1 | Cuming, NE | 0.6 | 10 | $50 to $500 | ||
| June 4 | 7:00 PM CDT | F0 | Franklin, NE | 0.5 | 10 | $500 to $5,000 |
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.