317
FXUS65 KMSO 122116
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
316 PM MDT THU MAR 12 2026
DISCUSSION
KEY MESSAGES:
- SNOW LEVELS LOWERING INTO THE VALLEYS TONIGHT CAUSING WINTRY
TRAVEL, ESPECIALLY ALONG AND NORTH OF INTERSTATE 90.
- VALLEYS IN NORTH CENTRAL IDAHO (GRANGEVILLE TO ELK CITY) WILL
REMAIN IN MODERATE TO HEAVY RAIN, ELEVATING THE RISK FOR
ROCKFALLS, SNOW SLOUGHING, AND MINOR RIVER RISES.
- AN ARCTIC BOUNDARY MOVING INTO WESTERN MONTANA(70% CHANCE)
SATURDAY EVENING WILL TAP INTO INSTABILITY TO TRIGGER INTENSE
BANDS OF SNOW BETWEEN KALISPELL TO MISSOULA/ALONG I-90/HWY200.
WITH WET ROADS FROM DAYTIME MELTING, A RAPID FREEZE-UP AND SLICK
ROADS ARE POSSIBLE.
THE COLD FRONT RESPONSIBLE FOR THIS MORNING'S DAMAGING WINDS HAS
EXITED THE REGION, THOUGH STRONG FLOW ALOFT CONTINUES TO PRODUCE
MOUNTAIN RIDGE GUSTS OF 40 TO 60 MPH. WHILE LINGERING SHOWERS MAY
BRIEFLY TRANSPORT HIGHER MOMENTUM TO VALLEY FLOORS, THE THREAT OF
WIDESPREAD DAMAGING WINDS HAS DIMINISHED, EXCEPT FOR LEMHI COUNTY
WHERE STRONG WINDS WILL PERSIST THROUGH EARLY EVENING.
ATTENTION SHIFTS TO AN ANOMALOUS ATMOSPHERIC RIVER STALLED FROM
THE WA/OR BORDER INTO WEST-CENTRAL MONTANA. THE PRIMARY FORECAST
CHALLENGE REMAINS SNOW LEVELS; HEAVY PRECIPITATION RATES ARE
EXPECTED TO DRIVE SNOW LEVELS BELOW MODEL GUIDANCE VIA TOP-DOWN
COOLING. VALLEYS IN NORTHWEST MONTANA ARE LIKELY TO SEE SEVERAL
INCHES OF ACCUMULATION BY MORNING. ALONG THE INTERSTATE 90
CORRIDOR, INCLUDING MISSOULA, THE FORECAST IS MORE NUANCED. A
SLIGHT LOWERING OF SNOW LEVELS TONIGHT COULD RESULT IN 1 TO 4
INCHES OF HEAVY, WET SNOW FOR SANDERS, MINERAL, MISSOULA, GRANITE,
AND POWELL COUNTIES. GIVEN THE POTENTIAL FOR SLUSHY
ACCUMULATIONS, WINTER WEATHER ADVISORIES MAY BE REQUIRED.
CONVERSELY, FURTHER SOUTH NEAR GRANGEVILLE AND ELK CITY,
PRECIPITATION WILL REMAIN PREDOMINANTLY RAIN, MAINTAINING AN
ELEVATED RISK FOR ROCKFALLS AND SNOW SLOUGHING.
A SHORTWAVE TROUGH WILL TRANSIT THE REGION ON SATURDAY MORNING,
ERODING THE SUBTROPICAL MOISTURE PLUME AND INTRODUCING GUSTY
POST- FRONTAL WINDS UP TO 35 MPH. AS THE ATMOSPHERE BECOMES HIGHLY
UNSTABLE BY SATURDAY AFTERNOON, SNOW AND GRAUPEL SHOWERS WILL
DEVELOP. OF SIGNIFICANT CONCERN IS AN ARCTIC BOUNDARY PROJECTED TO
PLUNGE SOUTH FROM ALBERTA SATURDAY EVENING (70% PROBABILITY).
THIS FRONT WILL LIKELY TRIGGER INTENSE SNOW BANDS BETWEEN
KALISPELL AND MISSOULA AND EASTWARD TOWARD THE CONTINENTAL DIVIDE.
RAPIDLY FALLING TEMPERATURES ON WET ROADS MAY CREATE A HIGH RISK
FOR FLASH FREEZE CONDITIONS AND DANGEROUS TRAVEL BEFORE ACTIVITY
WANES BY MIDNIGHT.
SUNDAY PROVIDES A BRIEF, COLD REPRIEVE BEFORE OVERRUNNING MOISTURE
FROM A BRITISH COLUMBIA-BOUND ATMOSPHERIC RIVER REACHES THE
REGION SUNDAY NIGHT. THIS WARM-FRONTAL PASSAGE WILL LIKELY
REINTRODUCE WINTRY TRAVEL IMPACTS TO THE MOUNTAINS AND NORTHERN
VALLEYS. LOOKING AHEAD TO NEXT WEEK, ENSEMBLE GUIDANCE STRONGLY
FAVORS THE BUILDING OF A HIGH-AMPLITUDE RIDGE. DESPITE OCCASIONAL
"DIRTY" RIDGE CLOUD COVER, A SIGNIFICANT WARMING TREND IS
EXPECTED, WITH TEMPERATURES REBOUNDING INTO THE 50S AND 60S.
AVIATION
GUSTY WESTERLY WINDS WILL PERSIST ACROSS THE NORTHERN
ROCKIES THIS AFTERNOON INTO THE EVENING, BUT THE THREAT OF
DAMAGING WINDS HAS SUBSIDED. THE ATMOSPHERIC RIVER WILL CONTINUE
TO PERSIST OVER THE NORTHERN ROCKIES THROUGH SATURDAY. THE BULK OF
THE MOISTURE WILL BE STREAMING OVER NORTH CENTRAL IDAHO INTO WEST
CENTRAL MONTANA KEEPING KMSO AND KHRF WITH LOW CLOUDS AND LIGHT
PRECIPITATION. SNOW LEVELS ARE GOING TO CONTINUE TO BE THE BIGGEST
ISSUE. KGPI WILL MOST LIKELY REMAIN ALL SNOW FOR ANY PERIODS OF
PRECIPITATION, CAUSING IFR CONDITIONS WHEN A SHOWER GOES OVER. THE
PRECIPITATION TYPE FOR KMSO AND KHRF WILL BE TRANSITIONING FROM
RAIN TO SNOW OVER THE NEXT 24 HOURS. THE THREAT OF PRECIPITATION
AT KSMN AND KBTM WILL BE LESS, BUT ANY PRECIPITATION THAT DOES
OCCUR IS EXPECTED TO BE SNOW.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER STORM WARNING UNTIL NOON MDT SATURDAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS...BUTTE/BLACKFOOT REGION...
LOWER CLARK FORK REGION...WEST GLACIER REGION.
WINTER STORM WARNING FROM 6 PM THIS EVENING TO NOON MDT SATURDAY
FOR POTOMAC/SEELEY LAKE REGION.
ID...WINTER STORM WARNING UNTIL 11 AM PDT SATURDAY FOR NORTHERN
CLEARWATER MOUNTAINS...SOUTHERN CLEARWATER MOUNTAINS.
HIGH WIND WARNING UNTIL MIDNIGHT MDT TONIGHT FOR EASTERN LEMHI
COUNTY...WESTERN LEMHI COUNTY.
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