297
FXUS65 KMSO 302009
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
109 PM MST SUN NOV 30 2025
DISCUSSION
KEY MESSAGES:
- WIDESPREAD WINTER TRAVEL IMPACTS (MON–TUE): SNOW IS EXPECTED TO
COVER ROADS, CREATING SLICK CONDITIONS.
- ACTIVE PATTERN CONTINUES (LATE WEEK): A MIX OF MOISTURE AND
COLD GROUND TEMPERATURES COULD BRING ADDITIONAL ROUNDS OF SLICK
TRAVEL.
LOW CLOUDS HAVE DEVELOPED IN THE LAST 24 HOURS ACROSS THE REGION.
THIS IS POSSIBLY DUE TO THE RELEASE OF MOISTURE FROM LAKES AND
RIVERS WITHIN THE MODIFIED ARCTIC AIR MASS IN PLACE. FORECAST
SOUNDINGS DEPICT THIS CONTINUING THROUGH MONDAY MORNING. IN THE
FLATHEAD VALLEY, EXTENDING NORTHWARDS, THE SOUNDINGS SHOW THE
CLOUD LAYER THICKENING ENOUGH THAT THERE COULD BE CONCERN THAT
FINE SNOW CRYSTALS OR EVEN FREEZING DRIZZLE COULD START TO FALL.
THIS IS VERY TOUGH TO PREDICT, BUT JUST WANTED TO THROW THAT OUT
THERE THAT THERE IS A LOW PROBABILITY BUT IMPACTFUL IF IT OCCURS.
CONFIDENCE CONTINUES TO GROW THAT A WIDESPREAD SNOW EVENT WILL
DEVELOP ON MONDAY AND LAST THROUGH TUESDAY. ACROSS NORTHWEST
MONTANA, THE SNOW COULD DEVELOP AS EARLY AS MONDAY MORNING, BUT
MORE LIKELY IN THE AFTERNOON. A KEY IMPACT TO THIS WILL BE THE
FACT THAT ANY MELTING SNOW DURING THE AFTERNOON COULD FREEZE-UP
AFTER NIGHTFALL MONDAY EVENING. YOU ADD RELATIVELY DRY SNOW ON TOP
OF THAT, IT COULD BECOME VERY SLICK. WITH THAT IN MIND, WE WANTED
TO GET THE MESSAGE OUT EARLY ENOUGH FOR NORTHWEST MONTANA, SO WE
ISSUED ADVISORIES. SNOW AMOUNTS COULD VARY WIDELY DURING THIS
EVENT, AS SEEN IN THE WEATHER MODELS. MUCH OF THE VARIANCE IS
LIKELY DUE TO RESOLUTION DIFFERENCES IN BEING ABLE TO ACCURATELY
DESCRIBE THE ARCTIC AIRMASS IN PLACE (A KNOWN BIAS). THERE ARE
INDICATIONS THAT FLATHEAD LAKE COULD HELP TO ENHANCED SNOWFALL
FROM BIGFORK TO POINTS NORTH AND EAST (I.E. MANY LAKES REGION,
FOOTHILLS OF THE NORTHERN SWAN RANGE). OTHER REGIONS MAY NEED
ADVISORIES ISSUED IN SUCCESSIVE SHIFTS. THE MISSOULA AND
BITTERROOT VALLEYS WILL BE A CHALLENGING FORECAST AS TOTAL
PRECIPITATION AMOUNTS RANGE FROM SEVERAL HUNDREDTHS UP TO A COUPLE
OF TENTHS. THIS COULD EASILY BRING A DUSTING TO SEVERAL INCHES OF
SNOW. THE GFS MODEL SEEMS TO BE HANDLING THE COLD AIR IN PLACE
BETTER THAN SOME OTHERS, AND SHOWS SNOW DEVELOPING IN MISSOULA BY
MID-AFTERNOON MONDAY, BUT THEN SHOWS SOME DRYING MONDAY EVENING
BEFORE ANOTHER ROUND OF SNOW DEVELOPS MONDAY NIGHT.
THIS PATTERN WITH NORTHERLY FLOW CAN FAVOR THE LOWER ELEVATIONS
OF IDAHO, PARTICULARLY THE CAMAS PRAIRIE. AS THE TROUGH PASSES
SOUTHWARDS ON TUESDAY, SNOW MAY DEVELOP AND LINGER FOR SEVERAL
HOURS. THIS COULD ALSO BE A BLACK ICE SCENARIO THAT NEEDS TO BE
WATCHED.
AFTER SNOW SHOWERS WANE BY WEDNESDAY MORNING, THERE WILL BE A
BRIEF LULL UNTIL THE NEXT SYSTEM STARTS TO ARRIVE BY LATER
THURSDAY! TEMPERATURES WILL BE NEAR SEASONAL LEVELS, ALTHOUGH SOME
LOCATIONS MAY HAVE PERSISTENT CLOUDS THAT COULD KEEP TEMPERATURES
COOLER.
THE FIREHOSE OF MOISTURE GETS POINTED IN OUR DIRECTION BY FRIDAY
AND SATURDAY. A DEEP TROUGH OF LOW PRESSURE SITUATED NEAR HAWAII
IS RESPONSIBLE FOR A LONG FETCH OF SUBTROPICAL MOISTURE REACHING
THE NORTHERN LATITUDES! THE DETAILS ON PRECIPITATION TYPE AND HOW
MUCH ARE A LITTLE BIT MORE FUZZY. BOTH THE ECMWF AND GFS ENSEMBLES
SHOW A HIGH PROBABILITY FOR THE COLDER AIRMASS HANGING ON OVER
MUCH OF OUR REGION, EXCEPT ACROSS SOUTHERN IDAHO COUNTY AND LEMHI
COUNTY LATER THURSDAY INTO FRIDAY. THEN THEY BOTH SHOW
OVERRUNNING PRECIPITATION DURING THE DAY WITH SOME TYPE OF EROSION
OF THE COLD AIR IN PLACE. IT COULD BE QUITE THE SLOPPY DAY AROUND
HERE WITH FREEZING RAIN, SNOW, RAIN, WIND, AND MODERATING
TEMPERATURES. THEY BOTH SHOW A LITTLE BIT OF COOLING BY SATURDAY
WHICH COULD EQUATE TO LOWER SNOW LEVELS. ALSO TO THROW INTO THE
MIX IS THE FACT THAT THIS NORTHWEST FLOW PATTERN CAN BE A
CONSIDERABLE SNOW- MAKING PATTERN FOR BOTH VALLEYS AND MOUNTAINS.
ALSO NORTHWEST FLOW CAN LEAVE THE GLACIER REGION AND/OR NORTHWEST
MONTANA VULNERABLE TO ARCTIC AIR INTRUSIONS.
AVIATION
LOW CLOUDS WILL BE STUCK IN THE VALLEYS THROUGH
MONDAY. THERE IS A LOW PROBABILITY FOR LIGHT FREEZING DRIZZLE OR
FLURRIES ACROSS NORTHWEST MONTANA EMANATING OUT OF THE STRATUS.
WIDESPREAD LIGHT TO MODERATE SNOWFALL WILL DEVELOP BY MONDAY
AFTERNOON ACROSS NORTHWEST MONTANA, THEN A SECOND SURGE OF
MOISTURE IMPACTING MUCH OF THE REGION BY MONDAY NIGHT INTO
TUESDAY. MOUNTAIN OBSCURATIONS, LOW CEILINGS AND VISIBILITY WILL
BE POSSIBLE MONDAY INTO TUESDAY AREA-WIDE.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY FROM 1 PM MONDAY TO 11 AM MST TUESDAY
FOR KOOTENAI/CABINET REGION.
WINTER WEATHER ADVISORY FROM 2 PM MONDAY TO 5 PM MST TUESDAY FOR
FLATHEAD/MISSION VALLEYS...LOWER CLARK FORK REGION...
POTOMAC/SEELEY LAKE REGION...WEST GLACIER REGION.
ID...NONE.
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