A large and complex weather system from the Pacific moved across north central Idaho to end the year. This system had 3 major impacts on the region.
Every event with a place to put it; 7 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 3 major impacts on the region. First, a tight surface pressure gradient, along with strong upper level winds produced high 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 rain and snow mix or just rain. Third, the warm, moist air mass pruduced areas of heavy rain which produced rock slides and released 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 28, 9:35 AM MST, 1 hour 25 minutes earlier.
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MISSOULA MT
935 AM MST WED DEC 28 2011
.DISCUSSION...SNOW LEVELS ARE CURRENTLY RISING ABOVE MANY OF THE
MOUNTAIN PASSES ALONG THE MONTANA/IDAHO BORDER THIS MORNING AND
SNOW ACCUMULATIONS WILL THUS HOLD OFF UNTIL LATE THIS EVENING.
LOST TRAIL PASS IS THE EXCEPTION SINCE THE ELEVATION IS HIGH
ENOUGH FOR SNOW TO CONTINUE. A WINTER WEATHER ADVISORY HAS BEEN
ISSUED FOR LOST TRAIL PASS TO ACCOUNT FOR THE SNOW AND WIND THAT
IS EXPECTED FROM NOW THROUGH THURSDAY MORNING. LOLO AND LOOKOUT
PASSES WINTER WEATHER ADVISORIES HAVE BEEN CANCELLED.
&&
.AVIATION...THE MAIN AVIATION IMPACTS FOR THE NEXT 24 HOURS WILL BE
MOUNTAIN OBSCURATIONS...STRONG MOUNTAIN TOP WINDS...AND INCREASED
WINDS AT LOW ELEVATIONS MAINLY THIS AFTERNOON THROUGH TONIGHT. A
FEW GUSTS COULD APPROACH 40 MPH AT TIMES. EXPECT LOWERING
CEILINGS AT TIMES AS WELL. WARMER TEMPERATURES WILL KEEP ANY
PRECIPITATION THAT FALLS TO BE RAIN BELOW AROUND 5500 FEET.
&&
.PREV DISCUSSION... /ISSUED 509 AM MST WED DEC 28 2011/
UPDATE...ADDED LEMHI COUNTY TO THE WIND ADVISORY
DISCUSSION...WINDS IN SOME AREAS OF LEMHI COUNTY ARE GUSTING TO
35 MPH. WINDS ARE EXPECTED TO INCREASE AND PEAK LATER THIS MORNING
THUS THE WIND ADVISORY ISSUANCE.
AVIATION...2 MAJOR AVIATION IMPACTS THE NEXT 24 HOURS WILL BE THE INCREASE
OF MOUNTAIN OBSCURATIONS AND STRONG GUSTY WINDS AT TIMES. GUSTS OF 20-30
MPH ARE POSSIBLE AT ALL TERMINALS WEDNESDAY AND WEDNESDAY NIGHT. A FEW
GUSTS COULD APPROACH 40 MPH AT TIMES. EXPECT THESE LOWERING CEILINGS
AND PERSISTENT STRONG WEST WINDS AT ALL TERMINALS. TEMPERATURES WILL
WARM UP SIGNIFICANTLY SO ANY PRECIPITATION THAT FALLS WILL BE IN
THE FORM OF RAIN.
PREV DISCUSSION... /ISSUED 356 AM MST WED DEC 28 2011/
.STRONG WINDS...MOUNTAIN SNOW...AND VALLEY RAIN THROUGH
THURSDAY...
DISCUSSION...STRONG WEATHER SYSTEM HAS NOW MOVED INTO THE REGION
AND WILL PERSIST THROUGH THURSDAY. LITTLE CHANGE IN THE OVERALL
FORECAST OF THE STRONG WESTERLY FLOW ALOFT. THIS WILL CONTINUE TO
PUMP MOIST PACIFIC AIR INTO THE REGION. A SOUTHWESTERLY FLOW
ALOFT COMBINED WITH A TIGHT SURFACE PRESSURE GRADIENT WILL SUPPORT
STRONG SURFACE WINDS WITH MORE WIND HIGHLIGHTS POSSIBLE. HIGH
CONFIDENCE FOR WIDESPREAD GUSTY WINDS AS ADVERTISED THE LAST
SEVERAL DAYS, THIS WILL BRING 3 SIGNIFICANT WEATHER IMPACTS OVER
THE NORTHERN ROCKIES THROUGH THURSDAY...
MODERATE SNOW ACCUMULATIONS OVER MOUNTAIN PASSES. WINTER WEATHER
ADVISORIES ARE IN EFFECT FOR LOLO...LOOKOUT AND MARIAS PASSES
STRONG WINDS ACROSS MANY VALLEYS AND HIGHER ELEVATIONS...ESPECIALLY
IMPACTING THE CAMAS PRAIRIE...BITTERROOT VALLEY AND THE I-90
CORRIDOR FROM GARRISON JUNCTION TO BUTTE. WINDS WILL PEAK THIS
MORNING THEN REMAIN STRONG THIS AFTERNOON AND TONIGHT THEN PEAK
ONCE AGAIN THURSDAY.
HEAVY RAINFALL AMOUNTS AND WARMER TEMPERATURES AT LOWER
ELEVATIONS MAY IMPACT CURRENT ICE JAMS. RAINFALL IN THE LIBBY
AREA COULD AMOUNT TO AS MUCH ONE INCH FROM TONIGHT THROUGH
THURSDAY NIGHT. RAINFALL THAT LEADS TO RUNOFF MAY ADD ENOUGH WATER
TO FLOWER CREEK TO BEGIN BREAKING UP ICE.
A COLD FRONT WILL PASS THROUGH THE REGION FRIDAY AND FRIDAY
NIGHT...USHERING IN COLDER UNSTABLE AIR AND GOOD CHANCE OF SNOW
SHOWERS WITH LIGHT ACCUMULATIONS DOWN TO THE VALLEY FLOORS.
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...2 MAJOR AVIATION IMPACTS THE NEXT 24 HOURS WILL BE THE INCREASE
OF MOUNTAIN OBSCURATIONS AND STRONG GUSTY WINDS AT TIMES. GUSTS OF 20-30
MPH ARE POSSIBLE AT ALL TERMINALS WEDNESDAY AND WEDNESDAY NIGHT. A FEW
GUSTS COULD APPROACH 40 MPH AT TIMES. EXPECT THESE LOWERING CEILINGS
AND PERSISTENT STRONG WEST WINDS AT ALL TERMINALS. TEMPERATURES WILL
WARM UP SIGNIFICANTLY SO ANY PRECIPITATION THAT FALLS WILL BE IN
THE FORM OF RAIN.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WIND ADVISORY UNTIL 5 PM MST THIS AFTERNOON BUTTE/BLACKFOOT
REGION.
WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR MARIAS
PASS.
ID...WIND ADVISORY UNTIL 7 AM PST THURSDAY FOR THE CAMAS PRAIRIE AND
HIGHWAY 95 BETWEEN WHITE BIRD AND RIGGINS.
WINTER WEATHER ADVISORY UNTIL 8 AM MST THURSDAY FOR LOST TRAIL
PASS.
WIND ADVISORY UNTIL 5 PM MST THIS AFTERNOON EASTERN LEMHI COUNTY.
&&
SHORT TERM...KITSMILLER/MEAD
PREV....RPN
AVIATION...KITSMILLERPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
507 AM MST WED DEC 28 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0303 AM NON-TSTM WND GST GRANGEVILLE 45.93N 116.12W
12/28/2011 M58.00 MPH IDAHO ID OFFICIAL NWS OBS
GRANGEVILLE 1 N REPORTED SOUTH WIND 39MPH WITH A GUST TO
58 MPH.
0315 AM NON-TSTM WND GST GRANGEVILLE 45.93N 116.12W
12/28/2011 M51.00 MPH IDAHO ID OFFICIAL NWS OBS
GRANGEVILLE ID AIRPORT REPORTED SOUTH WIND 35 MPH WITH A
GUST TO 51 MPH.
&&
LAKEThe national radar mosaic for the moment the first event began.
3 strong wind, 2 high wind, 1 heavy snow, 1 debris flow. Local standard time, as filed.
The Montana Department of Transportation reported a 24 hour snowfall of 11 to 14 inches at Lost Trail Pass.
A rock slide on Highway 37, mile marker 9, near Libby was caused by heavy rainfall.
A horse arena was damaged by strong winds in the town of Ramsay.
Strong winds were reported by the public near Woods Bay. Tree limbs were down and shingles blown off roofs.
Wind damage was reported in Charlos Heights when the top 60 feet of a 100 foot ponderosa pine snapped off and demolished a bedroom. Other trees and houses were damaged in the area.
A wind gust of 61 mph was reported 4 miles west-northwest of Darby.
A shed and tree were damaged 5 miles east of Florence.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Montana in 2011Every state in 2011This day in weather historyWarnings in Montana, 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: 356630, 356622, 356638, 356633, 356636, 356624, 356629.