Tornadoes · United States · Montana · 2007

EF0 tornado, Bigfork, Montana, July 18, 2007

Name: EF0 tornado, Bigfork, Montana, July 18, 2007
Start: 2007-07-19T02:40:00.000Z
End: 2007-07-19T03:30:00.000Z
Location: Bigfork, Montana

This EF0 tornado ran 8.0 miles across Flathead County on July 18, 2007, touching down at 8:40 PM MDT and reaching 50 yards wide. It killed nobody, and did $8,000 of property damage.

The rating scale

Tracks are drawn in the color of the rating. The Enhanced Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

EF065 to 85 mphthis tornado
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
EF186 to 110 mph
Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.
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.
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.
EF4166 to 200 mph
Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.
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.
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: EF0
Date: July 18, 2007
Touchdown: 8:40 PM MDT (02:40 UTC)
Lifted: 9:30 PM MDT (03:30 UTC)
On the ground: 50 minutes
Path length: 8.0 miles (12.9 km)
Path width: 50 yards (46 m)
Deaths: 0
Injuries: 0
Property damage: $8,000
County: Flathead County
Touchdown point: 47.963, -114.136
Lift-off point: 48.070, -114.070
Record number: 0707182040-01

What the Weather Service recorded

On July 18, an intensely strong shortwave trough moved to the northeast across Western Montana during the late afternoon and evening hours. The breaking of a strong mid level cap released copious amount of low level instability which aided in the rapid development of severe thunderstorm super cells.

The public reported a waterspout on Flathead lake along the Flathead/Lake County line. A sailboat at this location was spun around at least once in a counterclockwise direction and then sank.

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

The warnings

2 minutes of warning. NWS MSO issued a tornado warning for this county at 02:38 UTC, 2 minutes before the tornado touched down, in force until 03:30 UTC.

The county was under a severe thunderstorm watch, issued at 01:20 UTC and running to 07:00 UTC.

Issued (UTC)	Expired	Product	Office
01:20 UTC	07:00 UTC	Severe Thunderstorm Watch	MSO
02:24 UTC	03:15 UTC	Severe Thunderstorm Warning	MSO
02:38 UTC	03:30 UTC	Tornado Warning	MSO
03:08 UTC	04:15 UTC	Severe Thunderstorm Warning	MSO
03:24 UTC	06:30 UTC	Flash Flood Warning	MSO
04:07 UTC	04:45 UTC	Severe Thunderstorm Warning	MSO

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 01:03 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.

What forecasters said that day

The local office's own words before the tornado touched down, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Missoula, MT wrote its last area forecast discussion before the tornado touched down at Jul 18, 8:27 PM MDT, 13 minutes earlier.

Area forecast discussion, Jul 18, 8:27 PM MDT, 13 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
827 PM MDT WED JUL 18 2007

.UPDATE...UPDATED TO INCLUDE THUNDERSTORM COVERAGE IN NORTHWEST
MONTANA THIS EVENING. A SEVERE THUNDERSTORM WATCH HAS BEEN
ISSUED...PLEASE SEE GTFWOU7 FOR DETAILS.

&&

.AVIATION...STRONG THUNDERSTORMS ARE EXPECTED OVER NORTHWEST
MONTANA THIS EVENING. LIGHTNING HAIL AND WIND WILL EFFECT FLIGHT.
PLEASE SEE APPROPRIATE TAFS AND TWEBS.

&&

.PREV DISCUSSION... /ISSUED 243 PM MDT WED JUL 18 2007/

..RECORD SETTING HEAT WAVE TO CONTINUE...

DISCUSSION...THOUGH THE HEAT WAVE IS EXPECTED TO CONTINUE AT
LEAST THROUGH THE WEEKEND THE MAIN STORY THIS AFTERNOON AND
EVENING WILL BE FOR SCATTERED...WET THUNDERSTORMS. THESE ARE EXPECTED
TO DEVELOP DURING THE MID TO LATE AFTERNOON AND MOVE TO THE
NORTHEAST. MODEL WIND PROFILES SUGGEST THAT A COUPLE OF STORMS
COULD PRODUCE STRONG WIND GUSTS AND SMALL HAIL. ISOLATED
THUNDERSTORMS ARE EXPECTED TO CONTINUE INTO THE OVERNIGHT AS A
WEAK WAVE MOVES ACROSS NORTH CENTRAL IDAHO AND NW MT INTO THE
EARLY MORNING HOURS. ON THURSDAY...THE INFLUX OF DRIER AIR AND THE
MIXING DOWN OF UPPER LEVEL WINDS (TO CREATE BREEZY CONDITIONS IN
THE AFTERNOON) MAY LEAD TO CRITICAL FIRE WEATHER CONDITIONS.
THEREFORE...A SLIGHT INCREASE IN THE COVERAGE OF SMOKE ACROSS THE
AREA MAY BE OBSERVED AS THE WIND INTERACTS WITH THE WILDFIRES
THAT ARE SCATTERED ACROSS THE AREA.

FRIDAY THROUGH WEDNESDAY...SOUTHWESTERLY UPPER LEVEL FLOW WILL
CONTINUE THROUGH THE MIDDLE OF NEXT WEEK. THIS WILL BRING
UNSTABLE...BUT DRY AND CONTINUED WARM CONDITIONS TO MOST OF THE
AREA. UNSTABLE CONDITIONS ARE EXPECTED TO MIX FAIRLY STRONG MID
LEVEL WINDS TO THE SURFACE DURING THE AFTERNOON HOURS. THERE WILL
BE A MINIMAL THREAT OF THUNDERSTORMS AS WELL INTO NEXT WEEK.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...FIRE WEATHER WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY
     EVENING FOR DEERLODGE/WEST BEAVERHEAD-EAST BEAVERHEAD-EAST
     LOLO.
 ...SEVERE THUNDERSTORM WATCH IN EFFECT UNTIL 1AM THURSDAY FOR NORTHWEST
    MONTANA.

ID...NONE.
&&

UPDATE...STEGEMILLER/FOSTER
PREVIOUS...HENRY/STEGEMILLER
AVIATION...STEGEMILLER

Hazardous weather outlook, Jul 18, 9:52 AM MDT, 10 hours 48 minutes before

HAZARDOUS WEATHER OUTLOOK...CORRECTION
NATIONAL WEATHER SERVICE MISSOULA MT
952 AM MDT WED JUL 18 2007

IDZ005>010-MTZ001>007-043-191100-
NORTHERN CLEARWATER MOUNTAINS-SOUTHERN CLEARWATER MOUNTAINS-
OROFINO/GRANGEVILLE REGION-LOWER HELLS CANYON/SALMON RIVER REGION-
WESTERN LEMHI COUNTY-EASTERN LEMHI COUNTY-KOOTENAI/CABINET REGION-
WEST GLACIER REGION-FLATHEAD/MISSION VALLEYS-
LOWER CLARK FORK REGION-MISSOULA/BITTERROOT VALLEYS-
BITTERROOT/SAPPHIRE MOUNTAINS-BUTTE/BLACKFOOT REGION-
POTOMAC/SEELEY LAKE REGION-
952 AM MDT WED JUL 18 2007 /852 AM PDT WED JUL 18 2007/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
IDAHO...NORTHWEST MONTANA AND WEST CENTRAL MONTANA.

.DAY ONE...TODAY AND TONIGHT

SCATTERED STRONG THUNDERSTORMS WILL DEVELOP ACROSS PORTIONS OF
WESTERN AND NORTHWESTERN MONTANA THIS AFTERNOON...PERSISTING INTO
THE LATE EVENING HOURS. GUSTY WINDS AND SMALL HAIL WILL BE
POSSIBLE WITH ANY STORM THAT DEVELOPS. A COUPLE OF THESE STORMS
COULD BECOME SEVERE. HEAVY RAIN WILL BE POSSIBLE WITH SOME STORMS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

TEMPERATURES WILL REMAIN WELL ABOVE NORMAL. BREEZY WINDS IN THE
AFTERNOON MAY CREATE AREAS OF SMOKE THROUGH THE PERIOD ESPECIALLY
OVER THE CAMAS PRAIRIE AND OTHER VALLEY LOCATIONS.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

In the hours before

Local storm report, Jul 18, 3:21 PM MDT, 5 hours 19 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
321 PM MDT WED JUL 18 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0800 PM     TSTM WND DMG     RAVALLI                 47.28N 114.18W
07/17/2007                   LAKE               MT   NWS EMPLOYEE

            REPORT OF ONE LARGE TREE BLOWN DOWN...SEVERAL LARGE
            BRANCHES BROKEN AND IN ROAD.

&&

DICKERSON

Local storm report, Jul 18, 3:23 PM MDT, 5 hours 17 minutes before

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE MISSOULA MT
323 PM MDT WED JUL 18 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0800 PM     TSTM WND DMG     RAVALLI                 47.28N 114.18W
07/17/2007                   LAKE               MT   NWS EMPLOYEE

            REPORT OF ONE LARGE TREE BLOWN DOWN...SEVERAL LARGE
            BRANCHES BROKEN AND IN ROAD.

&&

DICKERSON

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.

Spokane, WA (KOTX), 00:00Z

2.7 hours before the tornado, 175 km from the path. July 19, 2007.

Skew-T log-p

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.

Hodograph

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: 114 J/kg
Mixed-layer CIN: -269 J/kg
Surface CAPE: 936 J/kg
Mixed-layer LCL: 1909 m above ground
0-6 km bulk shear: 58 kt
0-1 km bulk shear: 8 kt
0-1 km storm-relative helicity: 51 m²/s²
0-3 km storm-relative helicity: 130 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1
0-3 km lapse rate: 7.9 K/km

Open this sounding in Storm Lab

Spokane, WA (KOTX), 12:00Z

9.3 hours after it, 175 km from the path. July 19, 2007.

Skew-T log-p

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.

Hodograph

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: -55871 J/kg
Surface CAPE: 229 J/kg
Mixed-layer LCL: 1026 m above ground
0-6 km bulk shear: 73 kt
0-1 km bulk shear: 23 kt
0-1 km storm-relative helicity: -159 m²/s²
0-3 km storm-relative helicity: -377 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3
0-3 km lapse rate: 5.8 K/km

Open this sounding in Storm Lab

The surface observations

Kalispell (GPI), 34 km from the path, in the two hours either side.

Time (UTC)	Temp (°F)	Dew point (°F)	Wind	Gust (kt)	Pressure (mb)	Weather
00:55 UTC	96	53	340° 4 kt		1005.8
01:55 UTC	88	56	340° 4 kt		1005.4
02:02 UTC	87.8	57.2	350° 6 kt		1005.1	TS
02:58 UTC	91.4	53.6	150° 42 kt		1004.7	-TSRA
03:14 UTC	71.6	64.4	180° 15 kt	35	1008.1
03:21 UTC			180° 15 kt	35		TSRA
03:31 UTC
03:55 UTC	71.6		330° 10 kt		1008.8	-TSRA
04:13 UTC

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

The radar

The Missoula radar (KMSX), 109 km away, was scanning. The volume nearest the touchdown began at 02:42 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.

What was reported nearby

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

Time (UTC)	Report	Where	County	Remark
01:50 UTC	TSTM WND DMG	10 Wnw Pablo	Lake, MT	NUMEROUS LARGE TREES AND BRANCHES SNAPPED IN HALF OR UP ROOTED FROM MICROBURST WINDS ESTIMATED UP TO 90 MPH. ONE FENCE SEVERELY DAMAGED FROM TREES BLOWN DOWN. ONE POWER POLE SNAPPED IN HALF.
01:50 UTC	HAIL 1.5	10 Wnw Pablo	Lake, MT	HOME OWNERS REPORTED 1 TO 1 1/2 INCH DIAMETER HAIL WITH MICROBURST WINDS.
01:55 UTC	TSTM WND DMG	4 W Pablo	Lake, MT	THREE BARNS WITH WOOD AND TIN ROOFS BLOWN OFF FROM MICROBURST WINDS. WIND SPEEDS ESTIMATED UP TO 90 MPH. ONE BARN ALSO HAD WALL STRUCTURE DAMAGE. TIN DEBRIS BLOWN TO THREE TENTHS OF MILE AWAY FROM BARN. TRUCK WINDOWS SHA
01:58 UTC	TORNADO	6 S Polson	Lake, MT	POLICE REPORT FROM THE PUBLIC OF A TORNADO TOUCHDOWN SOUTH OF POLSON. ALSO MANY TREES DOWN SOUTH OF POLSON WITH ONE TREE FALLEN THROUGH HOME OWNERS ROOF.
02:00 UTC	TSTM WND DMG	2 Sw Polson	Lake, MT	NWS STORM SURVEY TEAM FOUND FLAG POLE BENT OVER. MEDIUM SIZED TREES AND BRANCHES OBSERVED DOWN. ESTIMATED 80 TO 90 MPH WINDS.
02:01 UTC	HAIL 1	Polson	Lake, MT	UNSPECIFIED WIND DAMAGE AS WELL.
02:05 UTC	TSTM WND DMG	2 N Polson	Lake, MT	LARGE TREES AND LIMBS BLOWN DOWN ON ROCKY POINT ROAD...POSSIBLY TORNADO DAMAGE. ALSO PENNY SIZE HAIL COVERING THE GROUND 4 INCHES DEEP.
02:05 UTC	TSTM WND GST 60	Ronan	Lake, MT	100FT TALL TREES LEANING OVER.
02:05 UTC	TORNADO	6 S Polson	Lake, MT	MANY TREES DOWN. ON TREE FELL THROUGH A HOME ROOF.
02:06 UTC	TSTM WND DMG	2 W Polson	Lake, MT	16 INCH TREE DIAMETER SNAPPED, 3/4 INCH HAIL AS WELL.
02:06 UTC	NON-TSTM WND DMG	2 W Polson	Lake, MT	16 INCH TREE DIAMETER SNAPPED, 3/4 INCH HAIL AS WELL.
02:07 UTC	TORNADO	5 N Polson	Lake, MT	PUBLIC NOTIFIED EMERGENCY MANAGEMENT OF AN OBSERVED WATERSPOUT OVER FLATHEAD LAKE.
02:10 UTC	TSTM WND GST 60	Ronan	Lake, MT
02:15 UTC	FUNNEL CLOUD	Polson	Lake, MT	OVER FLATHEAD LAKE.
02:15 UTC	TSTM WND GST 67	Big Arm	Lake, MT
02:22 UTC	TSTM WND GST 60	Big Arm	Lake, MT	TREES BLOWN OVER...UNSPECIFED SIZE.
02:22 UTC	TSTM WND GST 60	Ronan	Lake, MT	EVERGREEN TREES BLOWN DOWN.
02:30 UTC	TSTM WND DMG	Rollins	Lake, MT	SEVERAL LARGE PINE TREES 18 INCHES IN DIAMETER UPROOTED AND BLOWN OVER. ONE PINE TREE FELL ON CABIN AND DAMAGED ROOF. 6 MILES NORTH OF ROLLINS AT LUTHERN BIBLE CAMP, NUMEROUS TREES DOWNED ALONG AND OVER ACCESS ROAD.
02:40 UTC	TORNADO	5 Sw Woods Bay	Flathead, MT	POSSIBLE WATERSPOUT OVER FLATHEAD LAKE ON THE COUNTY LINE SPUN A 26 FOOT SAIL BOAD AROUND 360 DEGREES AT LEAST ONCE IN COUNTER CLOCKWISE MOTION AND THEN SANK IT. 2 ON BOARD WERE IN WATER OVER TWO HOURS BEFORE BEING RESCU
02:44 UTC	TSTM WND GST 70	Somers	Flathead, MT
02:50 UTC	TSTM WND DMG	3 Se Kalispell	Flathead, MT	CARPENTERS ARENA 60 FOOT ROOF BLOWN OFF AND THROWN 150 YARDS. ONE HORSE KILLED.
02:54 UTC	TSTM WND DMG	2 Nne Somers	Flathead, MT	THUNDERSTORM WINDS SNAPPED TREES AND UPROOTED A LARGE COTTONWOOD TREE THAT HAD A DIAMETER OF 4 FEET. SIGNIFICANT DAMAGE TO OUTBUILDINGS WAS OBSERVED. SHINGLES ON ROOF BLOWN OFF. WIND SPEED ESTIMATE OF 80 MPH.
02:54 UTC	TSTM WND DMG	Somers	Flathead, MT	LARGE TREES 8 TO 12 INCH IN DIAMETER SNAPPED IN HALF AND UPROOTED. ROOF BLOWN OFF BARN. SILO BLOWN OVER.
02:55 UTC	HAIL 1	4 W Pablo	Lake, MT
02:59 UTC	TSTM WND GST 68	Kalispell	Flathead, MT	M68 MPH WIND GUST CAUSED ROOF DAMAGE TO THE OUTLAW INN IN KALISPELL. POWER IS OUT IN MOST SECTIONS OF THE CITY.
03:00 UTC	FUNNEL CLOUD	5 N Bigfork	Flathead, MT	FUNNEL CLOUD OBSERVED IN SKY ALONG HIGHWAY 35.
03:00 UTC	TSTM WND DMG	5 N Bigfork	Flathead, MT	16-20 INCH DIAMETER TREES BLOWN DOWN.
03:00 UTC	TSTM WND DMG	Bigfork	Flathead, MT	6-8 INCH TREES BLOWN DOWN.
03:00 UTC	TSTM WND DMG	Kila	Flathead, MT	GARDEN STRUCTURE DAMAGE. 5 TO 7 INCH DIAMETER TREE BLOWN OVER.
03:00 UTC	TSTM WND DMG	W Kila	Flathead, MT	BARN ROOF BLOWN OFF FROM THUNDERSTORM WINDS.
03:32 UTC	HAIL 0.5	5 Sw Kalispell	Flathead, MT
03:50 UTC	HAIL 0.88	Kalispell	Flathead, MT	NICKEL SIZED HAIL REPORTED COVERING THE GROUND IN KALISPELL.
03:58 UTC	TSTM WND DMG	Lonepine	Sanders, MT	SEVERAL LARGE TREES BLOWN DOWN. WINDOWS BLOWN OUT ON MOBILE HOMES FROM STRAIGHT LINE WINDS.
04:00 UTC	TSTM WND DMG	Kalispell	Flathead, MT	POWER IS OUT OVER ALL OF FLATHEAD COUNTY.
04:10 UTC	TSTM WND DMG	5 N Bigfork	Flathead, MT	16-20 INCH DIAMETER TREES BLOWN DOWN.
05:00 UTC	FLOOD	Kalispell	Flathead, MT	URBAN FLOODING. MINOR STREET FLOODING REPORTED IN DOWNTOWN KALISPELL.
05:00 UTC	FLASH FLOOD	Kalispell	Flathead, MT	MINOR STREET FLOODING REPORTED IN DOWNTOWN KALISPELL.
05:30 UTC	FLOOD	Kalispell	Flathead, MT	URBAN FLOODING. SIGNIFICANT STREET FLOODING REPORTED IN KALISPELL.
05:30 UTC	FLASH FLOOD	Kalispell	Flathead, MT	SIGNIFICANT STREET FLOODING REPORTED IN KALISPELL.

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

This ground now

The live radar over the track Every 2007 tornado in Montana Every tornado in Montana since 1950 Warnings in force in Montana now The forecast where you are

The other tornadoes of July 18, 2007

3 more were confirmed in the United States that day.

Date	Time	Rating	Where	Path (mi)	Width (yd)	Damage
July 18	9:25 AM EDT	EF1	Suffolk, NY	0.7	150
July 18	7:15 PM CDT	EF1	Linn, IA	1.2	100	$50,000
July 18	7:50 PM MDT	EF0	Lake, MT	1.0	50	$8,000

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.