A large and complex weather system from the Pacific moved across north central Idaho to end the year. This system had three major impacts on the region.
Every event with a place to put it; 3 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 large and complex weather system from the Pacific moved across north central Idaho to end the year. This system had three major impacts on the region. First, a tight surface pressure gradient, along with strong upper level winds produced high surface winds. Second, abundant moisture with this system produced some heavy snowfall over the mountains, but since the air mass was warm, the lower elevations received a mix of rain and snow. Third, the warm, moist air mass produced areas of heavy rain which produced rock slides and the release of ice jams.
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 27, 1:46 PM PST, 13 hours 4 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
246 PM MST TUE DEC 27 2011
...A VERY WINDY PERIOD EXPECTED THROUGH THE REMAINDER OF THE
WEEK...
.DISCUSSION...
LITTLE CHANGE IN THE FORECAST FOR RAIN OR SNOW AMOUNTS FROM
YESTERDAY...CONFIDENCE IS HIGH IN A VERY WET WEEK FOR THE HIGH
COUNTRY WITH SOME RAIN SHOWERS IN THE VALLEYS. THE BIG CHANGE IN
THE FORECAST IS FOR WINDS ACROSS THE REGION. A JET STREAM
SUPPORTED BY VERY STRONG WINDS JUST ABOVE THE MOUNTAIN TOPS WILL
CAUSE WINDY CONDITIONS FROM CAMAS PRAIRIE AND GRANGEVILLE IN IDAHO
TO LOOKOUT...MARIAS...LOLO...AND MCDONALD PASSES. A WIND ADVISORY
WAS ISSUED FOR MOUNTAIN WAVE WINDS IN GRANGEVILLE TONIGHT THROUGH
THURSDAY MORNING. THE BITTERROOT VALLEY MAY ALSO SEE STRONG CROSS
WINDS ON HIGHWAY 93. STRONG WINDS ARE ALSO POSSIBLE ALONG THE I-90
CORRIDOR FROM GARRISON JUNCTION TO DEERLODGE. CONFIDENCE OF WINDS
GUSTING OVER 40 MPH IS NOT HIGH ENOUGH TO ISSUE AN ADVISORY
YET FOR THE I-90 CORRIDOR OR THE BITTERROOT VALLEY...BUT ONE MAY
BE ISSUED LATER. WINDS WILL PEAK WEDNESDAY MORNING THEN DECREASE
DURING THE DAY TO PEAK AGAIN THURSDAY MORNING.
TRAVELERS...ESPECIALLY THOSE IN HIGH PROFILE VEHICLES SHOULD USE
CAUTION WHEN TRAVELING IN THE BITTERROOT VALLEY OR ALONG I-90 ON
WEDNESDAY AND THURSDAY.
THURSDAY NIGHT AND FRIDAY...THE STRONG WESTERLY FLOW ALOFT WILL
CONTINUE TO PUMP MOIST PACIFIC AIR INTO THE NORTHERN ROCKIES
REGION. A SOUTHWESTERLY FLOW ALOFT COMBINED WITH A TIGHT SURFACE
PRESSURE GRADIENT WILL SUPPORT STRONG SURFACE WINDS WITH MORE WIND
HIGHLIGHTS POSSIBLE. A COLD FRONT IS EXPECTED TO PASS THROUGH THE
REGION FRIDAY...USHERING IN COLDER UNSTABLE AIR.
SATURDAY THROUGH TUESDAY...MEDIUM RANGE MODELS CONTINUE TO SHOW
SIGNIFICANT DIFFERENCES IN TIMING AND LOCATION OF LARGE SCALE
TROUGH/RIDGE FEATURES. THE OVERALL FORECAST CONSENSUS DOES TREND
TOWARDS MORE RIDGING NEXT WEEK AND DRIER MORE STABLE CONDITIONS.
&&
.AVIATION...THE MAJOR AVIATION IMPACT THE NEXT 24 HOURS WILL BE
THE INCREASE OF MOUNTAIN OBSCURATIONS AND WINDS OVERNIGHT INTO
WEDNESDAY. EXPECT LOWERING CEILINGS AT TIMES AT KGPI AND KMSO
TONIGHT. THESE IMPACTS WILL OCCUR AT ALL TERMINALS. A STRONG
WEATHER SYSTEM WILL MOVE THROUGH THE REGION TONIGHT THROUGH
WEDNESDAY AND PRODUCE SIGNIFICANT MOUNTAIN SNOW. HOWEVER VALLEY
LOCATIONS WILL REMAIN MAINLY DRY UNDER THE SHADOWING EFFECT FROM
STRONG WEST WINDS. WINDS WILL BEGIN TO INCREASE OVERNIGHT INTO
WEDNESDAY. GUSTS OF 20-30 MPH ARE POSSIBLE AT ALL TERMINALS AFTER
28/0900Z.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY UNTIL 5 PM MST WEDNESDAY FOR LOLO PASS.
WINTER WEATHER ADVISORY UNTIL 5 PM MST WEDNESDAY FOR MARIAS PASS.
WINTER WEATHER ADVISORY UNTIL 5 PM MST WEDNESDAY FOR I-90
LOOKOUT PASS TO HAUGAN.
ID...WIND ADVISORY FROM 7 PM THIS EVENING TO 7 AM PST THURSDAY FOR
THE CAMAS PRAIRIE AND HIGHWAY 95 BETWEEN WHITE BIRD AND
RIGGINS.
WINTER WEATHER ADVISORY UNTIL 4 PM PST WEDNESDAY FOR LOLO PASS.
&&
SHORT TERM...LEACH
LONG TERM....MSJ
AVIATION...KOLATAThe national radar mosaic for the moment the first event began.
3 high wind. Local standard time, as filed.
A wind gust of 58 mph was recorded at the Grangeville airport. Also Grangeville 1 n reported a south wind of 39 mph with a gust to 58 mph.
A wind gust of 58 mph was reported at the Grangeville airport with sustained winds out of the southwest at 47 mph.
The Skull Gulch RAWS, 11 miles west-southwest of Shoup, reported a gust of 81 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2011Every state in 2011This day in weather historyWarnings in Idaho, December 2011
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: 356604, 356623, 356626.