A cold Canadian system converged with a warm Pacific weather system to produced accumulating snow accross western Montana. Snow amounts ranged from eight to eighteen inches of new snow.
Every event with a place to put it; 6 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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.
The episode as NWS MSO wrote it up.
A cold Canadian system converged with a warm Pacific weather system to produced accumulating snow accross western Montana. Snow amounts ranged from eight to eighteen inches of new snow. In addition, as the strong cold front pushed through northwest Montana, northeast winds caused blowing and drifting snow and low visibilities.
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 Dec 11, 2:41 PM MST, 1 hour 19 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
241 PM MST FRI DEC 11 2009
...HEAVY SNOW EXPECTED OVER THE CLEARWATER MOUNTAINS AND THE WEST
GLACIER REGION SATURDAY INTO MONDAY...WITH WHITE-OUT CONDITIONS
POSSIBLE ALONG AND NEAR THE DIVIDE SATURDAY NIGHT AND SUNDAY...
.DISCUSSION...
TONIGHT AND SATURDAY...A CYCLONIC NORTHWEST FLOW ALOFT WILL
CONTINUE TO CIRCULATE MID/HIGH LEVEL MOISTURE INTO THE NORTHERN
ROCKIES TONIGHT. ON SATURDAY...A CANADIAN WEATHER SYSTEM WILL BE
APPROACHING NORTHWEST MONTANA...WHILE A SECOND PACIFIC LOW SYSTEM
WILL SPREAD MOISTURE INTO THE AREA FROM THE WEST. THE COMBINATION
OF THESE TWO WEATHER SYSTEMS WILL BRING HEAVY SNOWFALL TO THE
CLEARWATER MOUNTAINS OF NORTH-CENTRAL IDAHO BY AFTERNOON. FARTHER
NORTH OVER THE WEST GLACIER REGION...ARCTIC AIR PLUNGING SOUTH OUT
OF CENTRAL CANADA WILL BEGIN SPILL ACROSS THE PASSES. CONDITIONS
IN THE WEST GLACIER REGION WILL QUICKLY DETERIORATE MARKING A
PERIOD OF PROLONGED COLD...SNOWY...WINDY WEATHER.
SATURDAY NIGHT THROUGH SUNDAY NIGHT...WEATHER CONDITIONS WILL
CONTINUE TO DETERIORATE THROUGHOUT MUCH OF WESTERN MONTANA AND THE
IDAHO PANHANDLE AS WARMER MOIST AIR ORIGINATING FROM A PACIFIC
SYSTEM TO THE SOUTH INTERACTS WITH THE COLD CANADIAN WEATHER
SYSTEM. WHILE AN INTRUSION OF ARCTIC AIR IS EXPECTED INTO WESTERN
MONTANA...SOME UNCERTAINTY STILL EXISTS AS TO THE EXACT POSITION
AND MOVEMENT OF THE ARCTIC BOUNDARY ACROSS WEST-CENTRAL MONTANA.
THE LOCATION OF THIS BOUNDARY HAS HUGE IMPLICATIONS AS THE AMOUNT
OF SNOW...WIND AND COLD AIR IMPACTS WESTERN MONTANA.
WATCHES/WARNINGS HAVE BEEN ISSUED HIGHLIGHTING AREAS OF CONCERNS.
WARNED AREAS ARE EXHIBITING A GREATER SENSE OF FORECAST
CONFIDENCE IN HEAVY SNOW AND WHITE-OUT CONDITIONS. IN ADDITION...THE
WEST GLACIER REGION WILL HAVE TO DEAL WITH DANGEROUSLY COLD WIND
CHILLS ONCE THE NORTHEAST WINDS KICK IN SATURDAY NIGHT.
SOUTHWEST FLOW DEVELOPS OVER THE PACIFIC NORTHWEST BEHIND THE
EXITING TROUGH. THIS WILL BRING IN WARMER AIR ALOFT BUT GETTING THIS
WARMER AIR INTO THE TIGHTER VALLEYS WILL BE TOUGH WITH THE FRESH
SNOW COVER. THIS AIR WILL BE FAIRLY MOIST KEEPING THE POTENTIAL
FOR MORE SNOW AND POSSIBLY SOME RAIN IN CENTRAL IDAHO AND ALONG
THE MONTANA IDAHO BORDER. TEMPERATURES WILL SLOWLY MODERATE WITH
HIGHS NEARING AVERAGE BY LATE NEXT WEEK.
&&
.AVIATION...LIGHT SURFACE WINDS AND HIGH LEVEL CLOUDS CAN BE
EXPECTED THROUGH FRIDAY EVENING FOR THE NORTHERN ROCKIES. LIGHT
SNOW AND LOWERED CEILINGS WILL START TO SPREAD ACROSS NORTHWEST
MONTANA...BUT THE SIGNIFICANT ACCUMULATING SNOW...IMPACTING VIS
AND CEILINGS...IS NOT EXPECTED UNTIL AFTER THE 12/12Z-15Z WINDOW.
EXPECT SNOW TO CONTINUE AND ALSO SPREAD ACROSS WESTERN MONTANA
AND NORTH-CENTRAL IDAHO THROUGH THE WEEKEND...AS A MOIST PACIFIC
SYSTEM AND ANOTHER ARCTIC PUSH INTERACT OVER THE REGION. THE
PRESSURE GRADIENT WILL TIGHTEN WITH THE PUSH OF THE ARCTIC AIR
ALONG THE CONTINENTAL DIVIDE INCREASING SURFACE WINDS...MAINLY
IMPACTING KGPI AND SMALLER NORTHERN AIRFIELDS SATURDAY EVENING. STRONG
WINDS COUPLED WITH ANY NEW SNOW ACCUMULATION WILL INTRODUCE THE
POSSIBILITY FOR LOCAL WHITEOUT CONDITIONS ACROSS NORTHWEST MONTANA
LATER SATURDAY AFTERNOON.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY
AFTERNOON FOR LOWER CLARK FORK REGION.
WINTER STORM WARNING FROM 5 PM SATURDAY AFTERNOON THROUGH
5 PM MONDAY AFTERNOON FOR LOLO PASS.
WINTER STORM WATCH FROM SATURDAY AFTERNOON THROUGH LATE SUNDAY
NIGHT FOR FLATHEAD/MISSION VALLEYS.
WINTER STORM WARNING FROM 11 AM SATURDAY TO 5 AM MST MONDAY FOR
WEST GLACIER REGION.
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY
AFTERNOON FOR POTOMAC/SEELEY LAKE REGION.
WINTER STORM WATCH FROM SATURDAY EVENING THROUGH MONDAY
AFTERNOON FOR BUTTE/BLACKFOOT REGION.
ID...WINTER STORM WARNING FROM 10 AM SATURDAY TO 4 PM PST MONDAY FOR
NORTHERN CLEARWATER MOUNTAINS-SOUTHERN CLEARWATER MOUNTAINS.
&&
SHORT TERM...MSJ/FELSCH
LONG TERM....LOEFFELBEIN
AVIATION...NOLTEHAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE MISSOULA MT 236 PM MST FRI DEC 11 2009 MTZ005-121200- MISSOULA/BITTERROOT VALLEYS- 236 PM MST FRI DEC 11 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF WEST CENTRAL MONTANA. .DAY ONE...THIS AFTERNOON AND TONIGHT WIDESPREAD HAZARDOUS WEATHER IS NOT ANTICIPATED AT THIS TIME. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY ALTHOUGH UNCERTAINTY STILL EXISTS...MODERATE TO HEAVY SNOW IS POSSIBLE SATURDAY EVENING INTO MONDAY AS AN ARCTIC FRONT SHIFTS WESTWARD ACROSS THE CONTINENTAL DIVIDE AND STALLS NEAR WEST CENTRAL MONTANA. TRAVEL OVER AREA HIGHWAYS MAY BE DIFFICULT IN THIS TIME FRAME...AS LOCALIZED HEAVY SNOW IS POSSIBLE. GUSTY EAST WINDS MAY BE ENCOUNTERED TRAVELING EAST ALONG THE I-90 AND HIGHWAY 200 CORRIDORS...REDUCING VISIBILITY IN BLOWING SNOW. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES. MTZ001-121200- KOOTENAI/CABINET REGION- 236 PM MST FRI DEC 11 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHWEST MONTANA. .DAY ONE...THIS AFTERNOON AND TONIGHT WIDESPREAD HAZARDOUS WEATHER IS NOT ANTICIPATED AT THIS TIME. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY ALTHOUGH UNCERTAINTY STILL EXISTS...MODERATE TO HEAVY SNOW IS POSSIBLE SATURDAY AFTERNOON INTO EARLY SUNDAY MORNING...AND AGAIN SUNDAY NIGHT INTO MONDAY AS TWO WEATHER DISTURBANCES PASS THROUGH THE AREA. TRAVEL OVER AREA HIGHWAYS MAY BE DIFFICULT IN THIS TIME FRAME...AS LOCALIZED HEAVY SNOW IS POSSIBLE. GUSTY EAST WINDS MAY BE ENCOUNTERED TRAVELING EAST ALONG HIGHWAY 2 AND ALONG HIGHWAY 93...REDUCING VISIBILITY IN BLOWING SNOW. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES. IDZ007-121200- OROFINO/GRANGEVILLE REGION- 136 PM PST FRI DEC 11 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL IDAHO. .DAY ONE...THIS AFTERNOON AND TONIGHT WIDESPREAD HAZARDOUS WEATHER IS NOT ANTICIPATED AT THIS TIME. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY ALTHOUGH UNCERTAINTY STILL EXISTS...MODERATE TO HEAVY SNOW IS IS POSSIBLE SATURDAY AFTERNOON INTO SUNDAY ALONG AND NORTH OF THE HIGHWAY 12 CORRIDOR. TRAVEL ALONG HIGHWAY 12 AND THE GREER GRADE MAY BE DIFFICULT IN THIS TIME FRAME...AS LOCALIZED HEAVY SNOW MAY REDUCE VISIBILITY AND MAKE ROADS SLICK AND ICY. .SPOTTER INFORMATION STATEMENT... WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.
The national radar mosaic for the moment the first event began.
4 heavy snow, 2 winter storm. Local standard time, as filed.
A trained spotter 6 miles east of Ovando reported 18 inches of snow. A trained spotter in Avon reported 8 inches of snow.
A CoCoRaHS observer in Greenough reported 8 inches of snow. An NWS employee reported 12 inches in Clinton.
A trained spotter in Columbia Falls reported 9 inches of snow. A trained spotter 10 miles southwest of Kalispell reported 8 inches of snow. In addition, strong winds with the passing cold front caused a ground blizzard at Glacier International Airport for a period of time overnight on the 12th.
A trained spotter in Swan Lake reported 15 inches of snow. A trained spotter in Essex reported 14 inches of snow. In addition, high winds were reported by the DOT along Highway 2 from Marias Pass to Essex, making for low visibility.
A trained spotter 3 miles east of Lolo reported 8 inches of snow. A trained spotter in Miller Creek reported 8 inches of snow.
THE DOT over Lolo Pass reported 10 inches of new snow. Eight inches of new snow was reported over Lost Trail Pass.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2009Every state in 2009This day in weather historyWarnings in Montana, December 2009
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: 206695, 206696, 206692, 206691, 206693, 206694.