Montana, 2004

Debris Flow in Montana, August 20 to 21, 2004

August 20 to 21, 2004 · NWS MSO · 1 event in 1 county or zone

Heavy rain from thunderstorms caused a large rock and debris slide to occur near Haystack Creek from The Loop to Logan Pass in Glacier National Park. The large slide deposited about 2,000 cubic feet of rock and debris 150 feet wide and up to 12 feet deep onto the road.

Where it happened

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The toll

Deaths
0
Injuries
0
Property damage
None recorded
Crop damage
None recorded
Events
1

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 MSO wrote it up.

Heavy rain from thunderstorms caused a large rock and debris slide to occur near Haystack Creek from The Loop to Logan Pass in Glacier National Park. The large slide deposited about 2,000 cubic feet of rock and debris 150 feet wide and up to 12 feet deep onto the road. A passing motorist, whose car was damaged by falling rock, reported the rock side to park officials. Portions of the Going to the Sun road were closed for several days due to the slide.

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 Missoula, MT wrote its last area forecast discussion before the first event at Aug 20, 2:00 AM MST, 30 minutes earlier.

Area forecast discussion, Aug 20, 2:00 AM MST, 30 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
300 AM MDT FRI AUG 20 2004

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT...AN UPPER LEVEL
DISTURBANCE CROSSING IN A NORTHWEST FLOW ALOFT IS CURRENTLY
TRIGGERING AN AREA OF THUNDERSTORMS ACROSS PORTIONS OF NORTHWEST
MONTANA. EXPECT THIS WAVE TO CONTINUE TO PUSH SOUTHWARD AND
SERVE AS A TRIGGER FOR THIS AFTERNOON AND EVENINGS CONVECTION AS THE
ATMOSPHERE FURTHER DESTABILIZES. THE UPPER LEVEL RIDGE TO THE WEST
THAT HAS DOMINATED THE WEATHER PATTERN OVER THE LAST SEVERAL DAYS
WILL CONTINUE TO WEAKEN TODAY. SATURDAY A WEAK UPPER LEVEL TROUGH
WILL PUSH THROUGH THE INTERMOUNTAIN WEST...WITH THE FLOW BECOMING
SOUTHWESTERLY BY EARLY EVENING. THIS WILL ALLOW FOR SHOWER AND
THUNDERSTORM DEVELOPMENT...MAINLY OVER NORTHWEST MONTANA. SATURDAY
NIGHT AN APPROACHING LOW PRESSURE SYSTEM WILL MAKE FOR INCREASING
CHANCES FOR SHOWERS AND THUNDERSTORMS ACROSS MUCH OF THE
INTERMOUNTAIN WEST.

.LONG TERM...SUNDAY THROUGH FRIDAY...IT APPEARS A SIGNIFICANT SHIFT
IN THE UPPER FLOW PATTERN AND PLACEMENT OF RIDGES AND TROUGHS WILL
TAKE PLACE SUNDAY INTO MONDAY.  THE TROUGH OF LOW PRESSURE AND
ASSOCIATED COOL WEATHER MAY PERSIST MUCH OF NEXT WEEK. HAVE LOWERED
TEMPERATURES A FEW MORE DEGREES AND RAISED THE POPS A LITTLE TROUGH
THE EXTENDED PERIOD.
&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...NONE.
ID...NONE.
&&

SHORT TERM/GILCHRIST
LONG TERM/KOLATA

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

1 debris flow. Local standard time, as filed.

Debris Flow, West Glacier Region

When
August 20, 2:30 AM MST to August 21, 6:00 AM MST
Where
West Glacier Region forecast zone
Reported by
PARK/FOREST SERVICE
Coordinates
47.971, -114.069 (the zone’s center; the record gives no point)

What these are

Debris Flow
A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.

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

The same day elsewhere

More

Every storm in Montana in 2004Every state in 2004This day in weather historyWarnings in Montana, August 2004

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: 5420031.