902
FXUS65 KMSO 022000
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
100 PM MST TUE DEC 2 2025
DISCUSSION
KEY MESSAGES:
- SLICK TRAVEL CONTINUES: LINGERING LIGHT SNOW AND FOG WILL
CAUSE PERIODS OF SLOW DRIVING CONDITIONS.
- MID-WEEK LULL: A BRIEF BREAK IN WIDESPREAD PRECIPITATION IS
EXPECTED WEDNESDAY, THOUGH STABLE AIR MAY TRAP LOW CLOUDS AND
FREEZING FOG IN THE VALLEYS.
- COMPLEX LATE WEEK STORM: AN ACTIVE PATTERN RESUMES THURSDAY
INTO FRIDAY WITH A POTENT MOISTURE SURGE. THERE IS SIGNIFICANT
UNCERTAINTY REGARDING VALLEY SNOW LEVELS, WHICH WILL DETERMINE
WHETHER IMPACTFUL SNOW OR WINTRY MIX OCCURS IN LOWER
ELEVATIONS.
CURRENT SATELLITE AND RADAR IMAGERY SHOW THE BACK EDGE OF THE
TROUGH SLOWLY MOVING THROUGH NORTH-CENTRAL IDAHO AND WESTERN
MONTANA. WHILE THE HEAVIEST SNOWFALL RATES HAVE DIMINISHED, LIGHT
SNOW SHOWERS AND AREAS OF FREEZING FOG ARE CREATING LINGERING
SLICK SURFACES. AS THE UPPER-LEVEL SUPPORT SHIFTS EAST, WE EXPECT
PRECIPITATION TO TAPER OFF FROM WEST TO EAST BY THIS EVENING.
TONIGHT INTO WEDNESDAY, THE PRIMARY CONCERN SHIFTS TO LOW CLOUD
COVER AND FOG. WITH PARTIAL CLEARING ALOFT AND ABUNDANT MOISTURE
REMAINING IN THE BOUNDARY LAYER, PATCHY TO WIDESPREAD FREEZING FOG
IS LIKELY TO DEVELOP IN THE VALLEYS. THIS COULD LEAD TO RIME ICE
ACCRETION ON BRIDGES AND OVERPASSES FOR THE WEDNESDAY MORNING
COMMUTE. A TRANSIENT RIDGE WILL PROVIDE A BRIEF BREAK IN ACTIVE
WEATHER FOR MOST OF WEDNESDAY, KEEPING TEMPERATURES SEASONABLY
COOL BUT GENERALLY DRY.
PRECIPITATION WILL SPREAD INTO THE REGION DURING THURSDAY. THE
CRITICAL FORECAST CHALLENGE WILL BE THE "BATTLEGROUND" BETWEEN THE
COOL AIR CURRENTLY IN OUR VALLEYS AND THE INCOMING MILDER AIR
ALOFT. MODEL GUIDANCE SUGGESTS WELL ABOVE NORMAL MOISTURE
TRANSPORT, BUT THERMAL PROFILES ARE MARGINAL. WE EXPECT A PERIOD
OF OVERRUNNING SNOW AT ONSET FOR MOST LOCATIONS. HOWEVER, AS THE
MILDER AIR ALOFT STRENGTHENS FRIDAY, SNOW LEVELS ARE EXPECTED TO
RISE. THIS MAY TRANSITION VALLEY SNOW TO RAIN OR A WINTRY MIX,
PARTICULARLY FOR AREAS SOUTH OF I-90. NORTHWEST MONTANA VALLEYS
APPEAR MORE LIKELY TO HOLD ONTO THE COLD AIR LONGER, MAINTAINING
MOSTLY SNOW THROUGH MIDDAY FRIDAY.
CURRENT FORECASTS SHOW SNOW LEVELS PEAKING AROUND 5,000 FEET ON
SATURDAY. SATURDAY MORNING IS LOOKING PARTICULARLY CONCERNING
REGARDING THE POTENTIAL FOR VALLEY FREEZING RAIN. THIS RISK IS DUE
TO A HIGH LIKELIHOOD OF SHOWERS, UNCERTAINTY REGARDING THE EXACT
PRECIPITATION TYPE, AND SURFACE TEMPERATURES HOVERING NEAR
FREEZING. TRAVELERS PLANNING TRIPS FOR THE END OF THE WEEK AND
SATURDAY ARE ADVISED TO KEEP A CLOSE EYE ON THE FORECAST, AS SNOW
ACROSS MOUNTAIN PASSES AND A WINTRY MIX IN THE VALLEYS ARE
EXPECTED TO IMPACT TRAVEL CONDITIONS.
AVIATION
SNOW SHOWERS ARE MOVING SOUTH THIS AFTERNOON, AND WILL
CONTINUE TO IMPACT VISIBILITY AT KBTM AND KSMN THROUGH THE
AFTERNOON. A CLEARING AND DRYING TREND GOING INTO WEDNESDAY WILL
BRING THE THREAT FOR LOW STRATUS AND FOG TONIGHT AND ON WEDNESDAY
MORNING. EXPECT LOW CEILINGS DOWN TO ABOUT 1000 FT AT ALL NORTHERN
ROCKIES TERMINALS WEDNESDAY MORNING. RESIDUAL MOISTURE IN THE
LOWER ATMOSPHERE AND CALM TO LIGHT WINDS WILL PUT FOG IN THE TAFS
FOR KGPI AND KMSO.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR
BITTERROOT/SAPPHIRE MOUNTAINS...BUTTE/BLACKFOOT REGION...
POTOMAC/SEELEY LAKE REGION...WEST GLACIER REGION.
WINTER WEATHER ADVISORY UNTIL 2 PM MST THIS AFTERNOON FOR
MISSOULA/BITTERROOT VALLEYS.
ID...WINTER WEATHER ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR
NORTHERN CLEARWATER MOUNTAINS...SOUTHERN CLEARWATER
MOUNTAINS.
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