Flash Flood and Hail in Montana, July 22, 2008

Name: Flash Flood and Hail in Montana, July 22, 2008
Start: 2008-07-22T14:11
End: 2008-07-22T19:30
Location: Montana

July 22, 2008 · NWS TFX · 16 events in 3 counties and zones

A very unstable airmass allowed severe thunderstorms to develop over portions of Southwest Montana. Gallatin and Madison counties.

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 16

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS TFX wrote it up.

A very unstable airmass allowed severe thunderstorms to develop over portions of Southwest Montana. Hail the size of golf balls and wind gusts in excess of 60 mph were reported in Beaverhead...Gallatin and Madison counties. Heavy rain also caused flash flooding in Beaverhead County.

What forecasters said that day

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

NWS Great Falls, MT wrote its last area forecast discussion before the first event at Jul 22, 8:25 AM MST, 5 hours 46 minutes earlier.

Area forecast discussion, Jul 22, 8:25 AM MST, 5 hours 46 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
925 AM MDT TUE JUL 22 2008

.DISCUSSION...

UPDATE FORTHCOMING. HAVE MADE SOME ADJUSTMENTS TO THE POP GRIDS TO
BEETER ALIGN WITH NEIGHBORING OFFICES. ACTIVE WEATHER DAY STILL
ANTICIPATED ACROSS THE AREA. SPC HAS SOUTHWEST MONTANA AND EASTERN
PORTIONS OF THE COUNTY WARNING AREA UNDER A SLIGHT RISK TODAY. RADAR
RETURNS INDICATE LARGE AREA OF SHOWERS AND ISOLATED THUNDERSTORMS
WEST OF THE DIVIDE AND MOVING NORTHEAST ALREADY. REMAINDER OF
FORECAST LOOKS ON TRACK. EMANUEL

&&

.AVIATION...
UPDATED 1200Z.
EXPECT GENERALLY VFR CONDITIONS THROUGH TONIGHT. MOST AREAS WILL
EXPERIENCE SHOWERS/THUNDERSTORMS DURING THE PERIOD FROM 12Z TODAY
TO 12Z WEDNESDAY. IT IS HARD TO SAY EXACTLY HOW THE SHOWERS AND
THUNDERSTORMS WILL PLAY OUT DURING THE PERIOD...BUT HAVE A GENERAL
IDEA THAT SCATTERED SHOWERS AND THUNDERSTORMS WILL MOVE INTO SW
MONTANA THIS MORNING THEN SPREAD SLOWLY NORTHEAST THIS AFTERNOON
AND EVENING AND BECOME MORE NUMEROUS AS THEY DO SO. THERE WILL BE
A RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING...MAINLY
SOUTHEAST OF A LINE FROM HAVRE TO GREAT FALLS TO MISSOULA. SOME OF
THE SHOWERS AND THUNDERSTORMS WILL PRODUCE HEAVY RAIN WITH MVFR
AND IFR CONDITIONS THIS AFTERNOON THROUGH TONIGHT. ALSO AM FAIRLY
CONFIDENT THAT THERE WILL BE AN AREA OF RAIN/SHOWERS/THUNDERSTORMS
AFFECTING KGTF AND KCTB TO THE CONTINENTAL DIVIDE NEAR AND AFTER
MIDNIGHT WITH AGAIN THE POSSIBILITY OF MVFR/IFR CONDITIONS.
CONFIDENCE IN FORECAST WIND DIRECTIONS IS LOW BUT AT LEAST MOST WINDS
UNAFFECTED BY SHOWERS/THUNDERSTORMS WILL BE NEAR OR LESS THAN 10
KNOTS. BLANK

&&

.PREV DISCUSSION...ISSUED 339 AM MDT TUE JUL 22 2008

SEVERE THUNDERSTORMS WILL BE POSSIBLE THIS AFTERNOON AND
EVENING...AS A VERY MOIST AND VIGOROUS UPPER LEVEL TROUGH APPROACHES
THE REGION.

SCATTERED SHOWERS CONTINUE TO DEVELOP WEST OF THE CONTINENTAL DIVIDE
THIS MORNING IN CONJUNCTION WITH A LEAD SHORTWAVE TROUGH...AS CLOUD
COVERAGE INCREASES ACROSS THE ENTIRE AREA. AS THE DAY
PROGRESSES...LIFT ASSOCIATED WITH THE PRIMARY TROUGH WILL SPREAD
ACROSS THE REGION FROM SOUTHWEST TO NORTHEAST. SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO FORM BY LATE MORNING OVER SOUTHWEST
MONTANA...AND MOVE NORTHEASTWARD ACROSS THE REMAINDER OF THE REGION
THIS AFTERNOON AND EVENING. WITH COPIOUS AMOUNTS OF PACIFIC AND
MONSOONAL MOISTURE POOLING INTO THE REGION...IT WON/T TAKE MUCH OF A
KICKER TO GET STORMS GOING EARLY IN THE DAY...WHICH HAS THE
POTENTIAL TO LIMIT OVERALL SOLAR HEATING AND INSTABILITY. WIND
DIRECTIONS WILL BE FAIRLY UNIFORM WITH HEIGHT OVER SOUTHWEST
MONTANA...WHERE THE STRONGEST FLOW ALOFT AND THREAT FOR ORGANIZED
STRONG/SEVERE STORMS IS EXPECTED TO BE. THE MAIN THREAT INITIALLY
WILL BE LARGE HAIL AS COOLER AIR ALOFT WITH THE TROUGH APPROACHES
THE REGION...THOUGH THE DAMAGING WIND THREAT WILL INCREASE WITH TIME
AS CONVECTION BECOMES MORE ORGANIZED. THE SEVERE THREAT WILL EXTEND
NORTHEASTWARD TOWARD GREAT FALLS AND LEWISTOWN BY LATE AFTERNOON.
ALSO OF CONCERN IS THE HEAVY RAIN POTENTIAL...AS THE ATMOSPHERE WILL
BE VERY MOIST. WHILE A FLASH FLOOD WATCH WAS CONSIDERED...ESPECIALLY
FOR BURN AREAS...A MAJOR MITIGATING FACTOR FOR THE FLASH FLOOD
POTENTIAL WILL BE STRONG WINDS ALOFT AND FAST STORM MOTION...WITH
STORMS FORECAST TO MOVE TO THE NORTHEAST AT 15 TO 25 KNOTS.
HOWEVER...ANY CASES OF STORMS TRAINING OVER THE SAME LOCATIONS WILL
NEED TO BE CAREFULLY MONITORED FOR A FLASH FLOOD THREAT. AS
INSTABILITY DIMINISHES THIS EVENING...THE MAIN THREAT WILL
TRANSITION TO A HEAVY RAIN POTENTIAL...AS SHOWERS AND THUNDERSTORMS
DIMINISH FROM SOUTHWEST TO NORTHEAST...WITH ONLY ISOLATED ACTIVITY
EXPECTED BY DAWN ON WEDNESDAY. COOLER TEMPERATURES ARE EXPECTED
TODAY WITH INCREASED CLOUDINESS...AND TONIGHT AS WELL ONCE THE COLD
FRONT WILL HAVE CROSSED THE REGION. ANOTHER...ALBEIT
WEAKER...SHORTWAVE TROUGH WILL MOVE ACROSS THE FORECAST AREA
WEDNESDAY AFTERNOON/EVENING...RESULTING IN ISOLATED SHOWERS AND
THUNDERSTORMS...MAINLY OVER THE NORTHWEST HALF OF THE FORECAST AREA.
SOME OF THE STORMS COULD BE STRONG...GIVEN THE INCREASED
INSTABILITY...ESPECIALLY WITH LINGERING LOW LEVEL MOISTURE FROM THE
PRECEDING PRECIPITATION EVENT AND STRONG FLOW ALOFT MOVING THROUGH
THE REGION ONCE AGAIN. OTHERWISE...TEMPERATURES WILL BE NEAR
SEASONAL AVERAGE WITH PARTLY CLOUDY SKIES ON WEDNESDAY. FOR
THURSDAY...SINKING AIR DOWNSTREAM OF AN UPPER LEVEL RIDGE BUILDING
OVER THE WESTERN CONUS WILL LIMIT THE CHANCE FOR THUNDERSTORMS TO
FAR EASTERN PORTIONS OF THE FORECAST AREA...WITH TEMPERATURES NEAR
SEASONAL AVERAGES UNDER PARTLY CLOUDY SKIES. COHEN

THURSDAY NIGHT THROUGH SUNDAY NIGHT...MODELS FORECAST AN UPPER RIDGE
TO DEVELOP OVER THE AREA THURSDAY NIGHT AND CONTINUE OVER THE AREA
INTO FRIDAY. WITH THE UPPER RIDGE APPROACHING THE FORECAST AREA
THURSDAY NIGHT MODELS DO NOT FORECAST PRECIPITATION AND FEELING
CONFIDENT ENOUGH TO REMOVE ITS MENTION FROM THE FORECAST. LATEST
MODEL RUNS ARE ALSO DRY ON FRIDAY BUT PREVIOUS RUNS OF SOME OF THE
MODELS HAD PRECIPITATION SO WILL LEAVE THE SLIGHT CHANCE OF
PRECIPITATION FORECAST FOR SW MT AND THE NW MOUNTAINS. THEREAFTER
MODELS FORECAST SW FLOW ALOFT BUT DIFFER ON DETAILS OF WEAK EMBEDDED
SHORTWAVES. ALTHOUGH LATEST MODEL RUNS ARE MOSTLY DRY AM RELUCTANT
TO DROP THE MENTION OF PRECIPITATION AS IT DOES NOT TAKE MUCH
MOISTURE/LIFT THIS TIME OF YEAR TO GENERATE A FEW THUNDERSTORMS.
ENDED UP MAKING ONLY SOME MINOR CHANGES TO INHERITED CHANCE OF
PRECIPITATION FORECASTS. BLANK

MONDAY AND TUESDAY...LATEST MODELS CONTINUE TO DEPICT A WEST TO
SOUTHWEST FLOW OVER WEST AND CENTRAL MONTANA DURING THIS PERIOD.
MONSOONAL MOISTURE IS EXPECTED TO MOVE IN FROM THE SOUTH AND PROVIDE
A CHANCE FOR SHOWERS AND THUNDERSTORMS FOR THE SOUTHWEST MOUNTAINS
AND POSSIBLY THE NORTH CENTRAL PLAINS. USED CLIMO POPS THROUGH THE
PERIOD AND KEPT TEMPERATURES NEAR SEASONAL. SAUCIER

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  88  57  81  53 /  60  60  20  20
CTB  83  53  76  48 /  40  60  20  20
HLN  85  60  86  57 /  60  50  20  20
BZN  85  55  87  52 /  70  60  20  20
WEY  70  46  75  45 /  50  40  20  20
DLN  77  51  81  50 /  70  30  20  20
HVR  90  60  79  53 /  30  50  20  20
LWT  87  57  79  52 /  50  50  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...EMANUEL/COHEN
LONG TERM...BLANK/SAUCIER
AVIATION...BLANK

WEATHER.GOV/GREATFALLS

Hazardous weather outlook, Jul 22, 1:49 PM MST, 22 minutes before

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
249 PM MDT TUE JUL 22 2008

MTZ008-015-055-231230-
BEAVERHEAD-MADISON-GALLATIN-
249 PM MDT TUE JUL 22 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST
MONTANA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A SEVERE THUNDERSTORM WATCH IS IN EFFECT FOR
BEAVERHEAD...MADISON...AND GALLATIN COUNTIES UNTIL 9 PM MDT.

SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS SOUTHWEST MONTANA
IN ADVANCE OF A VERY MOIST PACIFIC STORM SYSTEM. SOME OF THE
THUNDERSTORMS MAY BECOME SEVERE...WHICH MEANS THEY MAY PRODUCE
HAIL GREATER THAN THE SIZE OF DIMES AND DAMAGING WINDS GREATER
THAN 55 MPH. ALL THUNDERSTORMS WILL BE CAPABLE OF PRODUCING HEAVY
RAINFALL. SHOWERS AND THUNDERSTORMS ARE EXPECTED TO CONTINUE INTO
THE EVENING...BEFORE DIMINISHING AFTER MIDNIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

ISOLATED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY
AFTERNOON AND EVENING. SOME OF THESE STORMS WILL HAVE THE
POTENTIAL TO PRODUCE WIND GUSTS TO 50 MPH AND HAIL TO THE SIZE OF
DIMES.

.SPOTTER INFORMATION STATEMENT...

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

MTZ009>014-044>054-231230-
NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-CASCADE-
CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-TOOLE-LIBERTY-
EASTERN PONDERA-BLAINE-SOUTHERN ROCKY MOUNTAIN FRONT-
EASTERN TETON-JUDITH BASIN-FERGUS-JEFFERSON-BROADWATER-MEAGHER-
249 PM MDT TUE JUL 22 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON
IN ADVANCE OF A VERY MOIST PACIFIC STORM SYSTEM. SOME OF THE
THUNDERSTORMS WILL BE CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING
WINDS...ESPECIALLY ALONG AND SOUTH OF A LINE FROM HELENA TO GREAT
FALLS TO LEWISTOWN. ALL THUNDERSTORMS WILL BE CAPABLE OF PRODUCING
HEAVY RAINFALL. SHOWERS AND THUNDERSTORMS ARE EXPECTED TO CONTINUE
INTO THE EVENING...BEFORE DIMINISHING AFTER MIDNIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

ISOLATED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE WEDNESDAY
AFTERNOON AND EVENING. SOME OF THESE STORMS WILL HAVE THE
POTENTIAL TO PRODUCE WIND GUSTS TO 50 MPH AND HAIL TO THE SIZE OF
DIMES.

.SPOTTER INFORMATION STATEMENT...

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

The radar

The Billings radar (KBLX), 187 km away, was scanning. The volume nearest the first event began at 21:11 UTC.

Open the radar archive at this moment

Event by event

10 hail, 5 thunderstorm wind, 1 flash flood. Local standard time, as filed.

Hail, Gallatin

When: July 22, 2:11 PM MST
Where: Gallatin County, 1 mi E of Bozeman
Measured: 0.75 in hail
Reported by: Public
Coordinates: 45.680, -111.009

A severe thunderstorm dropped .75 inch diameter hail at Bozeman 1E.

Hail, Beaverhead

When: July 22, 3:10 PM MST
Where: Beaverhead County, 4 mi W of Dillon
Measured: 1 in hail
Reported by: Trained Spotter
Coordinates: 45.220, -112.732

A severe thunderstorm dropped 1 inch diameter hail at Dillon 4W.

Thunderstorm Wind, Beaverhead

When: July 22, 3:13 PM MST
Where: Beaverhead County, Dillon
Measured: 56 kt (64 mph) estimated gust
Reported by: Trained Spotter
Coordinates: 45.220, -112.650

A severe thunderstorm produced a wind gust to 65 mph at Dillon.

Hail, Gallatin

When: July 22, 3:15 PM MST
Where: Gallatin County, 6 mi S of Bozeman
Measured: 1 in hail
Reported by: Trained Spotter
Coordinates: 45.593, -111.030

A severe thunderstorm dropped 1 inch diameter hail at Bozeman 6S.

Hail, Madison

When: July 22, 3:30 PM MST
Where: Madison County, Sheridan
Measured: 1.75 in hail
Reported by: Public
Coordinates: 45.450, -112.200

A severe thunderstorm dropped 1.75 inch diameter hail at Sheridan. Hail broke nearly every window on the south and west facing sides of the Sheridan high school and elementary school. Many homes suffered substantial hail damage as did vehicles and crops.

Flash Flood, Beaverhead

When: July 22, 3:32 PM MST to 7:30 PM MST
Where: Beaverhead County, 1 mi NE of Dillon to 0.5 mi E of Dillon
Cause: Heavy Rain
Reported by: Trained Spotter
Coordinates: 45.230, -112.635

Thunderstorms produced over six-tenths of an inch of rain in less than 20 minutes in Dillon. The resulting runoff caused water that was bumper deep on many streets in the city of Dillon.

Hail, Madison

When: July 22, 4:00 PM MST
Where: Madison County, 2 mi W of Sheridan
Measured: 0.88 in hail
Reported by: Trained Spotter
Coordinates: 45.450, -112.241

A severe thunderstorm dropped .88 inch diameter hail at Sheridan 2W.

Thunderstorm Wind, Madison

When: July 22, 4:05 PM MST
Where: Madison County, 2 mi W of Sheridan
Measured: 61 kt (70 mph) measured gust
Reported by: Trained Spotter
Coordinates: 45.450, -112.241

A severe thunderstorm produced a wind gust to 70 mph at Sheridan 2W.

Thunderstorm Wind, Madison

When: July 22, 4:09 PM MST
Where: Madison County, 1 mi W of Ennis
Measured: 74 kt (85 mph) measured gust
Reported by: COOP Observer
Coordinates: 45.350, -111.751

A severe thunderstorm produced a wind gust to 85 mph at Ennis 1W. Many trees and power lines were reported downed in Ennis. A roof was also blown off a building in Ennis.

Hail, Gallatin

When: July 22, 5:05 PM MST
Where: Gallatin County, 5 mi W of Bozeman
Measured: 1 in hail
Reported by: Trained Spotter
Coordinates: 45.680, -111.134

A severe thunderstorm dropped 1 inch diameter hail at Bozeman 5W.

Hail, Gallatin

When: July 22, 5:15 PM MST
Where: Gallatin County, Bozeman
Measured: 1.75 in hail
Reported by: Trained Spotter
Coordinates: 45.680, -111.030

A severe thunderstorm dropped 1.75 inch diameter hail at Bozeman, just south of the Montana state University campus.

Hail, Gallatin

When: July 22, 5:20 PM MST
Where: Gallatin County, Bozeman
Measured: 0.75 in hail
Reported by: Trained Spotter
Coordinates: 45.680, -111.030

A severe thunderstorm dropped .75 inch diameter hail at Bozeman.

Thunderstorm Wind, Gallatin

When: July 22, 5:20 PM MST
Where: Gallatin County, 20 mi N of Bozeman
Measured: 58 kt (67 mph) measured gust
Reported by: Trained Spotter
Coordinates: 45.969, -111.030

A severe thunderstorm produced a wind gust to 67 mph at Bozeman 20N. The anemometer broke at 67 mph.

Thunderstorm Wind, Gallatin

When: July 22, 5:22 PM MST
Where: Gallatin County, Belgrade
Measured: 50 kt (58 mph) measured gust
Reported by: ASOS
Coordinates: 45.780, -111.180

A severe thunderstorm produced a wind gust to 58 mph at the Bozeman ASOS site.

Hail, Gallatin

When: July 22, 5:25 PM MST
Where: Gallatin County, Bozeman
Measured: 0.75 in hail
Reported by: NWS Employee
Coordinates: 45.680, -111.030

A severe thunderstorm dropped .75 inch diameter hail at Bozeman, near the downtown area. Power was reported out throughout the city.

Hail, Gallatin

When: July 22, 5:25 PM MST
Where: Gallatin County, Bozeman
Measured: 1.75 in hail
Reported by: Trained Spotter
Coordinates: 45.680, -111.030

A severe thunderstorm dropped 1.75 inch diameter hail at Bozeman. Numerous homes on the south side of the city had broken windows.

What these are

Hail: Hail three-quarters of an inch or larger, or smaller hail that caused damage, filed with the largest stone measured.
Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Montana in 2008 Every state in 2008 This day in weather history Warnings in Montana, July 2008

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 123682, 123684, 123687, 123709, 123690, 124060, 123696, 123701, 123693, 123705, 123707, 123716, 123725, 123720, 123721, 123722.