737
FXUS65 KMSO 281943
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1243 PM MST MON NOV 28 2022
DISCUSSION
LIGHT SNOW IS EXPECTED TONIGHT ALONG THE I-90
CORRIDOR, PARTICULARLY FROM LOOKOUT PASS EASTWARD THROUGH ROUGHLY
DRUMMOND, AND POINTS SOUTH OF THIS CORRIDOR. THIS INCLUDES MOST OF
NORTH CENTRAL IDAHO AND THE MISSOULA AND BITTERROOT VALLEYS, LOLO
PASS, AND LOST TRAIL PASS. SNOW WILL PERSIST THROUGH THIS EVENING
AND INTO THE OVERNIGHT HOURS BEFORE TAPERING OFF NEAR OR ABOUT
SUNRISE TUESDAY. WHILE SNOW ACCUMULATIONS WILL GENERALLY BE ON THE
LIGHTER SIDE (ABOVE 4500 FEET: 2-6 INCHES, BELOW 4500 FEET: 1 TO
3 INCHES), TRAVEL ON TUESDAY MORNING COULD BE DIFFICULT AS A
RESULT IN THE AFOREMENTIONED LOCATIONS.
TUESDAY INTO WEDNESDAY WILL BE MOSTLY BENIGN WEATHER DAYS, SAVE
FOR MOUNTAINOUS TERRAIN ALONG THE MONTANA/IDAHO BORDER. THESE
AREAS WILL BEGIN TO SEE THE NEXT ROUND OF SNOWFALL STARTING
WEDNESDAY AFTERNOON (ABOVE 5000 FEET), PERSISTING THEREAFTER
THROUGH FRIDAY MORNING. THIS STORM WILL MAKE ITS WAY FURTHER OVER
THE NORTHERN ROCKIES, SPREADING ADDITIONAL SNOWFALL TO BOTH
MOUNTAINS AND VALLEYS ALIKE ON THURSDAY, WITH FURTHER ENHANCEMENT
OCCURRING THURSDAY NIGHT THROUGH FRIDAY MORNING AS IT SHIFTS
TOWARDS THE DIVIDE.
WHAT WE ARE CONFIDENT OF RIGHT NOW IS THAT SNOW WILL BECOME
WIDESPREAD THURSDAY INTO FRIDAY FOR ALL ELEVATIONS ACROSS WESTERN
MONTANA AND NORTH CENTRAL IDAHO. WE ALSO FEEL CONFIDENT THAT HEAVY
SNOWFALL WILL IMPACT TERRAIN ABOVE 4500 FEET, WITH THE HIGHEST
ACCUMULATIONS LIKELY ALONG THE MONTANA/IDAHO BORDER, AND ACROSS
NORTHWEST MONTANA, INCLUDING GNP, MARIAS PASS, AND SOUTH TOWARDS
MACDONALD PASS. STORM TOTAL SNOWFALL OF UP TO A FOOT OR MORE IS
EXPECTED FROM THIS SYSTEM LATE WEDNESDAY THROUGH EARLY FRIDAY,
EQUALING BETWEEN 0.75 AND 1.25 INCHES OF WATER EQUIVALENT. AS
SUCH, DIFFICULT TRAVEL WILL BE LIKELY OVER MOUNTAIN PASSES AND IN
THE BACKCOUNTRY DURING THIS TIME.
WHAT WE ARE LESS CONFIDENT ABOUT IS VALLEY SNOWFALL AMOUNTS. A
STRONG JET ALOFT WITH SOUTHWESTERLY FLOW OFTEN DECREASES THE
AMOUNT OF SNOW THAT MAKES IT DOWN TO VALLEY FLOORS, PARTICULARLY
IN VALLEYS SUCH AS THE BITTERROOT AND MISSOULA VALLEYS. WE SUSPECT
THIS WILL BE THE CASE EARLY ON IN THE STORM, BUT BY LATE
THURSDAY, CONDITIONS WILL BECOME MORE FAVORABLE FOR WIDESPREAD
VALLEY SNOWFALL TO OVERSPREAD NORTH CENTRAL IDAHO AND WESTERN
MONTANA VALLEYS (IF IT HASN’T STARTED BEFORE THEN ALREADY).
A RIDGE OF HIGH PRESSURE WILL ATTEMPT TO BUILD IN BEHIND THE
EXITING WINTER STORM ON SATURDAY, WHICH WOULD POINT TO DRY AND
COLD CONDITIONS ALONG WITH SOME LINGERING LIGHT SNOW SHOWERS FOR
NORTHWEST MONTANA MOUNTAINS.
AVIATION
SNOW SHOWERS THIS EVENING WILL INCREASE FROM NORTHWEST
TO SOUTHEAST ACROSS THE REGION WITH A SHORTWAVE MOVING THROUGH. AN
INCH OR TWO IS ALL THAT IS EXPECTED AT AREA TERMINALS WITH SOME
MVFR AND IFR CONDITIONS IN THE LATE OVERNIGHT AND EARLY MORNING
PERIODS. OVERALL CONDITIONS WILL START IMPROVE BETWEEN 29/12Z AND
29/18Z.
MSO WATCHES/WARNINGS/ADVISORIES
MT... WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 5 AM MST
TUESDAY FOR LOWER CLARK FORK REGION.
WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 5 AM MST
TUESDAY FOR BITTERROOT/SAPPHIRE MOUNTAINS...
MISSOULA/BITTERROOT VALLEYS.
ID...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 4 AM PST
TUESDAY FOR NORTHERN CLEARWATER MOUNTAINS...
OROFINO/GRANGEVILLE REGION...SOUTHERN CLEARWATER MOUNTAINS.
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