Tornadoes · United States · Montana · 1999

F0 tornado, Glasgow, Montana, June 21, 1999

This F0 tornado ran 0.1 miles across Valley County on June 21, 1999, touching down at 7:45 PM MDT and reaching 40 yards wide. It killed nobody.

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.

  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.

The record

Rating
F0
Date
June 21, 1999
Touchdown
7:45 PM MDT (01:45 UTC)
Path length
0.1 miles (0.2 km)
Path width
40 yards (37 m)
Deaths
0
Injuries
0
County
Valley County
Touchdown point
48.350, -106.850
Lift-off point
48.350, -106.850
Record number
945

What the Weather Service recorded

Over almost a four hour period, numerous severe thunderstorms moved from southwest to northeast across northeast Montana. These storms produced winds to 92 miles an hour, several small tornadoes and hail to a size of 1.75 inches. The community of Opheim was hit hardest by straight line winds and a weak tornado. Most of downtown Opheim was damaged including the front wall of the local hotel taken down. Power was out for most of the Opheim area for more than 18 hours. A state disaster declaration was declared for the Opheim area. The town of Froid suffered damage from straight line winds which pushed a concrete grain elevator off of its foundation. At the Fort Peck Lake Marina, significant damage was done to boats, docks and campers at the storms passed. One home in Fort Peck lost its roof.

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

The warnings

5 minutes of warning. NWS GGW issued a tornado warning for this county at 01:40 UTC, 5 minutes before the tornado touched down, in force until 02:45 UTC.

Issued (UTC)ExpiredProductOffice
00:51 UTC01:50 UTCSevere Thunderstorm WarningGGW
01:40 UTC02:45 UTCTornado WarningGGW

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 Slight Risk. The outlook in force was issued at 01:00 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.

Glasgow Intl Airport, MT (KGGW), 00:00Z

1.8 hours before the tornado, 23 km from the path. June 22, 1999.

Skew-T log-pSkew-T log-p diagram, Glasgow Intl Airport, MT at 00:00Z on 1999-06-22Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 2240 joules per kilogram, CIN -31, lifted condensation level 2482 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Glasgow Intl Airport, MT at 00:00Z on 1999-06-22The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 64 square meters per square second, 0 to 6 km bulk shear 45 knots.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
2240 J/kg
Mixed-layer CIN
-31 J/kg
Surface CAPE
2741 J/kg
Mixed-layer LCL
2482 m above ground
0-6 km bulk shear
45 kt
0-1 km bulk shear
15 kt
0-1 km storm-relative helicity
64 m²/s²
0-3 km storm-relative helicity
119 m²/s²
Significant tornado parameter
0.0
Supercell composite
5.5
0-3 km lapse rate
8.6 K/km

Open this sounding in Storm Lab

Glasgow Intl Airport, MT (KGGW), 12:00Z

10.2 hours after it, 23 km from the path. June 22, 1999.

Skew-T log-pSkew-T log-p diagram, Glasgow Intl Airport, MT at 12:00Z on 1999-06-22Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 0 joules per kilogram, CIN -81946, lifted condensation level 1274 meters above ground. Wind barbs in knots down the right edge.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Glasgow Intl Airport, MT at 12:00Z on 1999-06-22The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity -115 square meters per square second, 0 to 6 km bulk shear 62 knots.1939587897Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
0 J/kg
Mixed-layer CIN
-81946 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
1274 m above ground
0-6 km bulk shear
62 kt
0-1 km bulk shear
12 kt
0-1 km storm-relative helicity
-115 m²/s²
0-3 km storm-relative helicity
8 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.1 K/km

Open this sounding in Storm Lab

The surface observations

Glasgow International Airport (GGW), 23 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
23:56 UTC9359110° 8 kt995.6
00:56 UTC8859140° 7 kt996.3
01:25 UTC84.262.6160° 34 kt47997.6-TSRA SQ
01:56 UTC6661260° 31 kt491003TSRA
02:03 UTC64.460.8250° 27 kt391004.1TSRA BR
02:56 UTC6359320° 21 kt251001.7-TSRA

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

This ground now

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

The other tornadoes of June 21, 1999

3 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
June 215:10 PM MDTF0Fergus, MT0.210$3,000
June 217:43 PM MDTF0Phillips, MT0.250
June 218:30 PM MDTF1Valley, MT0.2100$250,000

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.