026
FXUS65 KMSO 262024
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
124 PM MST FRI DEC 26 2025
DISCUSSION
KEY MESSAGES:
- SNOW IMPACTS TRAVEL: TODAY THROUGH SATURDAY, STARTING ON PASSES
BUT TRANSITIONING INTO VALLEYS THIS EVENING. ISOLATED SNOW
SQUALLS POSSIBLE OVERNIGHT.
- HIGH WIND/OUTAGE RISK (TODAY): SOUTHWESTERLY GUSTS OF 30-45 MPH
(VALLEYS) AND 60+ MPH (MOUNTAINS) THROUGH THIS EVENING.
SATURATED SOILS WILL MAKE TREES MORE PRONE TO FALLING,
INCREASING THE RISK OF POWER OUTAGES.
- SATURDAY ARCTIC PUSH: FLASH FREEZE POTENTIAL AS BITTERLY COLD
AIR MOVES WEST OF THE DIVIDE SATURDAY MORNING. STRONG NORTHEAST
WINDS WILL DEVELOP IN PRONE CANYONS AND GAP AREAS (E.G., BAD
ROCK CANYON).
- BUILDING RIDGE (EARLY NEXT WEEK): COLD AND MUCH DRIER CONDITIONS
STARTING SUNDAY.
WATER VAPOR IMAGERY THIS AFTERNOON DEPICTS A BROAD LONGWAVE TROUGH
ESTABLISHED ALONG THE PACIFIC NORTHWEST COAST. AN EMBEDDED SHORTWAVE IS
CURRENTLY PIVOTING THROUGH THE TROUGH INTO NORTHWEST MONTANA, PROVIDING
SUFFICIENT LIFT FOR WIDESPREAD PRECIPITATION NORTH OF THE I-90 CORRIDOR.
THERMAL PROFILES REMAIN MARGINAL SOUTH OF THE HIGHWAY 2 CORRIDOR,
MAINTAINING A RAIN/SNOW MIX; HOWEVER, DYNAMIC COOLING AND HIGHER
PRECIPITATION RATES NORTH OF HIGHWAY 2 HAVE TRANSITIONED PRECIPITATION TYPE
TO ALL SNOW, LEADING TO VALLEY FLOOR ACCUMULATIONS. CONSEQUENTLY, THE
WINTER WEATHER ADVISORY FOR THE FLATHEAD VALLEY WAS ACCELERATED TO A
CURRENT START TIME.
SOUTH OF INTERSTATE 90, DEEPENING MIXING LAYERS ARE SUPPORTING
SOUTHWESTERLY GUSTS UP TO 45 MPH THROUGH THIS AFTERNOON. AS A COLD FRONT
TRAVERSES THE REGION THIS AFTERNOON, EXPECT A SHARP INCREASE IN SHOWER
COVERAGE AND A TRANSITION TO SNOW ABOVE 3,500 FEET, LIKELY IMPACTING TRAVEL
OVER MOUNTAIN PASSES.
A SECONDARY, MORE POTENT COLD FRONT WILL CROSS THE REGION TONIGHT INTO
SATURDAY MORNING, LOWERING SNOW LEVELS TO ALL VALLEY FLOORS ACROSS WESTERN
MONTANA AND NORTH-CENTRAL IDAHO. WHILE GUSTS ALONG THIS BOUNDARY WILL BE
SLIGHTLY WEAKER THAN TODAY'S WINDS, SATURATED SOILS INCREASE THE RISK FOR
ISOLATED TREE DAMAGE AND POWER OUTAGES. OF HIGHER CONCERN IS THE
POTENTIAL FOR CONVECTIVE SNOW SQUALLS ASSOCIATED WITH THE FRONTAL
PASSAGE AND STEEPENING LOW-LEVEL LAPSE RATES BEHIND IT. FORECAST
CONFIDENCE FOR REGIONAL SQUALL DEVELOPMENT IS MODERATE (30-50%),
THOUGH CONFIDENCE IN EXACT PLACEMENT REMAINS LOW. THESE FEATURES
WILL POSE A SIGNIFICANT RISK FOR FLASH FREEZE CONDITIONS AND RAPID
VISIBILITY REDUCTIONS TO NEAR ZERO WHERE SQUALLS DO DEVELOP. IF
YOU HAVE TRAVEL PLANS TONIGHT INTO EARLY SATURDAY, BE PREPARED FOR
WINTER DRIVING AND CHANGEABLE CONDITIONS!
BY SATURDAY MORNING, AN ARCTIC BOUNDARY WILL SPILL SOUTH ALONG THE
CONTINENTAL DIVIDE, BLEEDING WESTWARD THROUGH TERRAIN GAPS LIKE MARIAS PASS
INTO THE FLATHEAD VALLEY. THIS AIRMASS WILL PROVIDE A SECONDARY ROUND OF
FORCING, ENHANCING SNOWFALL AND ENSURING A FREEZE OF ANY LINGERING WET
SURFACES. PRESSURE GRADIENTS WILL SUPPORT GUSTS OF 40-50 MPH THROUGH THE
NORTHERN FLATHEAD VALLEY AND BAD ROCK CANYON.
AS THE ARCTIC AIRMASS SETTLES, A FRIGID SUNDAY MORNING IS EXPECTED.
SINGLE-DIGIT LOWS ARE FORECAST FOR MOST WESTERN MONTANA VALLEYS, WITH TEENS
ACROSS NORTH-CENTRAL IDAHO. ENSEMBLE CLUSTERS ARE IN HIGH AGREEMENT
REGARDING A BUILDING RIDGE OVER THE PACIFIC NORTHWEST FOR THE EARLY WORK
WEEK, LEADING TO A PERIOD OF STABILIZATION. HOWEVER, PERSISTENT NORTHWEST
FLOW ALOFT MAY ALLOW WEAK CLIPPER-LIKE DISTURBANCES TO MAINTAIN
LOW-PROBABILITY PRECIPITATION AND MORNING STRATUS/FOG.
CONFIDENCE IS HIGH (NEAR 80%) THAT THE RIDGE BREAKS DOWN BY NEXT THURSDAY
OR FRIDAY AS A DEEP PACIFIC TROUGH RE-ESTABLISHES ITSELF OVER THE
NORTHWEST, SIGNALING A RETURN TO A MORE ACTIVE, UNSETTLED PATTERN.
AVIATION
SEVERE TURBULENCE AND LLWS ARE THE PRIMARY CONCERNS
THIS AFTERNOON AS THE FIRST OF TWO FRONTAL FEATURES MOVES THROUGH
THE REGION. PIREPS CONFIRM SEVERE TURBULENCE (REPORTED BY A PC12
AT FL160 SE OF MSO) AND CONTINUOUS MODERATE TURBULENCE/LLWS ON
APPROACH INTO KMSO.
EXPECT SURFACE GUSTS TO 40 KNOTS AND POTENTIAL
MOUNTAIN WAVE ACTIVITY TO PERSIST THROUGH THE EVENING. CONVECTIVE
ELEMENTS EMBEDDED WITHIN THIS INITIAL WAVE MAY PRODUCE GRAUPEL,
HAIL, AND EVEN ISOLATED INTRACLOUD LIGHTNING (~10% PROBABILITY),
PARTICULARLY NEAR KMSO AND KBTM.
KGPI HAS TRANSITIONED TO SNOW EARLIER THAN ANTICIPATED; EXPECT
IFR/LIFR CONDITIONS WITH CEILINGS NEAR 1,000FT AND VISIBILITY
NEAR OR BELOW 3SM TO PERSIST IN SNOW AND FOG THROUGH THE EVENING.
A STRONGER COLD FRONT ARRIVES OVERNIGHT (ROUGHLY 04Z–09Z),
CRASHING FREEZING LEVELS TO VALLEY FLOORS REGION-WIDE. THIS
PASSAGE WILL LIKELY TRIGGER SNOW SQUALLS AND ORGANIZED BANDS,
BRINGING WIDESPREAD IFR CONDITIONS, REDUCED VISIBILITY, AND
CONTINUED STRONG GUSTS. BEHIND THIS FRONT, ATTENTION TURNS TO KGPI
LATE IN THE PERIOD (~19Z) WHERE WINDS WILL SHIFT NORTH/EAST,
MARKING THE ARRIVAL OF THE ARCTIC BOUNDARY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY UNTIL 2 PM MST SATURDAY FOR LOWER CLARK
FORK REGION.
WINTER WEATHER ADVISORY UNTIL 8 PM MST SATURDAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS...FLATHEAD/MISSION VALLEYS...
POTOMAC/SEELEY LAKE REGION.
WINTER WEATHER ADVISORY UNTIL 5 PM MST SATURDAY FOR
KOOTENAI/CABINET REGION...WEST GLACIER REGION.
WIND ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR
MISSOULA/BITTERROOT VALLEYS.
WINTER WEATHER ADVISORY FROM 2 AM TO 5 PM MST SATURDAY FOR
MISSOULA/BITTERROOT VALLEYS.
WIND ADVISORY UNTIL 5 AM MST SATURDAY FOR BUTTE/BLACKFOOT REGION.
WINTER WEATHER ADVISORY FROM 5 AM TO 8 PM MST SATURDAY FOR
BUTTE/BLACKFOOT REGION.
WIND ADVISORY UNTIL MIDNIGHT MST TONIGHT FOR POTOMAC/SEELEY LAKE
REGION.
ID...WINTER WEATHER ADVISORY UNTIL 1 PM PST SATURDAY FOR NORTHERN
CLEARWATER MOUNTAINS.
WINTER WEATHER ADVISORY UNTIL 8 PM MST /7 PM PST/ SATURDAY FOR
EASTERN LEMHI COUNTY...SOUTHERN CLEARWATER MOUNTAINS...
WESTERN LEMHI COUNTY.
WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 10 AM PST
SATURDAY FOR OROFINO/GRANGEVILLE REGION.
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