657
FXUS65 KMSO 172002
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
102 PM MST TUE DEC 17 2024
DISCUSSION
KEY MESSAGES:
- MIXED PRECIPITATION, INCLUDING FREEZING RAIN POSSIBLE TONIGHT
INTO WEDNESDAY MORNING ACROSS NORTHWEST MONTANA.
- STRONG GUSTY WINDS WEDNESDAY AFTERNOON IN THE MOUNTAINS AND
VALLEYS ALONG AND EAST OF HIGHWAY 93 IN WESTERN MONTANA.
- HIGH PRESSURE LATE IN THE WEEK INTRODUCES FOG AND LOW STRATUS
OUR NEXT WEATHER SYSTEM WILL BRING AN ATMOSPHERIC RIVER OVER THE
NORTHERN ROCKIES LATE THIS EVENING, THROUGH THE DAY WEDNESDAY.
SNOW-LEVELS WILL BEGIN TO RISE FROM SOUTH TO NORTH ACROSS THE
REGION THROUGH THE OVERNIGHT AS THE MOISTURE ARRIVES. SNOW LEVELS
ARE EXPECTED TO BE AS HIGH AS 6000 FEET IN AREAS SOUTH OF I-90 BY
WEDNESDAY AFTERNOON AND AROUND 4000-4500 FEET ACROSS NORTHWEST
MONTANA. THIS WILL BE A SCENARIO WHERE THE VALLEYS ALONG HIGHWAY 2
IN NORTHWEST MONTANA WILL RECEIVE ANOTHER ROUND OF LIGHT SNOW
AND/OR LIGHT FREEZING RAIN.
IN THE HIGHER ELEVATIONS, HEAVY, WET SNOW IS EXPECTED. FORECAST
MODELS SHOW A 70-80% CHANCE OF 6 INCHES OR MORE OF SNOW
ACCUMULATING ABOVE 5,000 FEET IN NORTHWEST MONTANA DURING THE 24
HOURS ENDING AT 5 PM WEDNESDAY. HIGHWAY 2 FROM WEST GLACIER TO MARIAS
PASS WILL SEE A COMBINATION OF GUSTY WINDS UP TO 50 MPH, REDUCING
VISIBILITY DUE TO HEAVY, BLOWING SNOW. A WINTER STORM WARNING HAS
BEEN ISSUED FOR THESE LOCATIONS.
ADDITIONALLY, A STRONG JET STREAM ON WEDNESDAY WILL BRING AN INCREASED RISK
OF GUSTY WESTERLY WINDS ACROSS WESTERN MONTANA. VALLEYS ALONG AND
EAST OF HIGHWAY 93 HAVE A 50-70% CHANCE OF SEEING WIDESPREAD
GUSTS OF 45 TO 55 MPH IN THE AFTERNOON AND EVENING. THERE IS A
70-75% PROBABILITY GUSTS WILL EXCEED 60 MPH ALONG I-90 FROM
DEERLODGE TO ANACONDA AND 20-30% IN THE BITTERROOT VALLEY. A
NUMBER OF HIGH WIND WARNINGS WILL GO INTO EFFECT IN THESE AREAS
FROM 11AM TO 11PM TOMORROW. SECURE ANY LOOSE OUTDOOR ITEMS AND IF
YOU ARE TRAVELING ON AREA ROADS IN A NORTH TO SOUTH ORIENTATION,
BE ADVISED THAT TRAVEL COULD BE VERY DIFFICULT FOR HIGH PROFILE
VEHICLES.
LOOKING AHEAD, A RIDGE OF HIGH PRESSURE IS EXPECTED TO BUILD OVER THE
NORTHERN ROCKIES THURSDAY AND FRIDAY, INCREASING THE POTENTIAL FOR FOG AND
LOW STRATUS CLOUDS EACH DAY. ABOUT 65% OF FORECAST MODELS SUGGEST THE RIDGE
WILL PERSIST INTO CHRISTMAS EVE, WHICH COULD DISRUPT HOLIDAY TRAVEL.
HOWEVER, SOME MODELS INDICATE A TROUGH OF LOW PRESSURE COULD MOVE IN,
BRINGING MOUNTAIN SNOW AND A RAIN/SNOW MIX TO THE VALLEYS.
AVIATION
A FIRST WAVE OF SNOW AND LOW ELEVATION RAIN WILL
BEGIN THIS AFTERNOON/EVENING BY ABOUT 18/0000Z. SNOW LEVELS WILL
BEGIN TO INCREASE OVERNIGHT TONIGHT, ALLOWING FOR A TRANSITION
FROM SNOW TO RAIN. A PERIOD OF FREEZING RAIN IS LIKELY TO OCCUR AS
THIS TRANSITION TAKES PLACE TONIGHT AND INTO WEDNESDAY MORNING,
MAINLY IMPACTING KGPI AND POSSIBLY KMSO. WEDNESDAY WILL BRING MORE
ACTIVE WEATHER. A SECOND WAVE OF PRECIPITATION WILL ARRIVE IN THE
MORNING, ABOUT 18/1200Z. INCREASING SNOW LEVELS WILL RESULT IN
RAIN AT THE TERMINALS. HIGH WINDS ARE LIKELY THROUGHOUT THE
NORTHERN ROCKIES ON WEDNESDAY. SOUTHERLY OR SOUTHWESTERLY WINDS
WILL INCREASE AND BECOME MOSTLY WESTERLY AFTER ABOUT 18/1900Z.
EXPECT GUSTS OF 40 TO 50 KNOTS IN THE AFTERNOON AT ALL TERMINALS
EXCEPT KSMN. AVIATORS SHOULD BE PREPARED FOR EVEN STRONGER WINDS
OVER THE MOUNTAIN CRESTS, OBSCURED TERRAIN, AND LOW-LEVEL
WIND SHEAR THROUGHOUT THE DAY ON WEDNESDAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 11 AM MST
WEDNESDAY FOR BITTERROOT/SAPPHIRE MOUNTAINS...
FLATHEAD/MISSION VALLEYS...KOOTENAI/CABINET REGION...LOWER
CLARK FORK REGION...POTOMAC/SEELEY LAKE REGION.
WIND ADVISORY FROM 11 AM TO 11 PM MST WEDNESDAY FOR
KOOTENAI/CABINET REGION...LOWER CLARK FORK REGION.
WINTER STORM WARNING FROM 5 PM THIS AFTERNOON TO 11 PM MST
WEDNESDAY FOR WEST GLACIER REGION.
HIGH WIND WARNING FROM 11 AM TO 11 PM MST WEDNESDAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS...BUTTE/BLACKFOOT REGION...
FLATHEAD/MISSION VALLEYS...MISSOULA/BITTERROOT VALLEYS...
POTOMAC/SEELEY LAKE REGION.
ID...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 10 AM PST
WEDNESDAY FOR NORTHERN CLEARWATER MOUNTAINS...SOUTHERN
CLEARWATER MOUNTAINS.
WIND ADVISORY FROM 11 AM MST /10 AM PST/ TO 11 PM MST /10 PM
PST/ WEDNESDAY FOR EASTERN LEMHI COUNTY...SOUTHERN
CLEARWATER MOUNTAINS...WESTERN LEMHI COUNTY.
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