625
FXUS65 KMSO 222137
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
237 PM MST MON DEC 22 2025
DISCUSSION
KEY MESSAGES:
- UNSETTLED HOLIDAY WEEK: A SERIES OF DISTURBANCES WILL KEEP THE REGION
WET AND UNSETTLED THROUGH CHRISTMAS. A STRONGER COLD FRONT ON
FRIDAY WILL LIKELY TRANSITION ALL VALLEY PRECIPITATION BACK TO
SNOW.
- NEW YEAR`S EVE OUTLOOK: A POTENTIAL ATMOSPHERIC RIVER COULD
BRING MILDER, WETTER, AND WINDIER CONDITIONS TO END THE YEAR.
A COMPLEX WEATHER PATTERN CONTINUES ACROSS THE NORTHERN ROCKIES AS MOIST
PACIFIC AIR OVERRIDES STUBBORN COLD AIR TRAPPED IN THE VALLEYS.
THIS SETUP WILL CREATE A VARIETY OF PRECIPITATION TYPES AND TRAVEL
HAZARDS THROUGH THE EARLY PART OF THE WEEK, FOLLOWED BY A SERIES
OF STORMS LEADING INTO THE CHRISTMAS HOLIDAY.
TONIGHT THROUGH TUESDAY: VALLEYS ACROSS LEMHI COUNTY, NORTH CENTRAL IDAHO,
AND SOUTHWEST MONTANA ARE EXPECTED TO COOL TO JUST BELOW FREEZING TONIGHT.
AS THE NEXT WAVE OF PRECIPITATION ADVANCES FROM SOUTH TO NORTH TUESDAY
MORNING, THERMAL PROFILES SUPPORT A WINTRY MIX OF SNOW AND FREEZING RAIN.
THIS WILL LIKELY CREATE SLICK TRAVEL CONDITIONS FOR LOWER ELEVATIONS,
INCLUDING THE SALMON AREA. WINTER WEATHER ADVISORIES HAVE BEEN ISSUED FOR
THESE LOCATIONS TO ADDRESS POTENTIAL TRAVEL IMPACTS. BY TUESDAY EVENING,
THE PULSE OF MOISTURE ARRIVES INTO NORTHWEST MONTANA, BRINGING LIGHT SNOW
TO MOUNTAIN PASSES AND MAINTAINING A WINTRY MIX FOR THE VALLEYS.
TEMPERATURES REMAIN MARGINAL. THE DIFFERENCE BETWEEN WET AND ICY
ROAD SURFACES WILL BE NARROW.
WEDNESDAY THROUGH SUNDAY: THE PATTERN REMAINS HIGHLY ACTIVE THROUGH THE
CHRISTMAS HOLIDAY. AN AMPLIFIED TROUGH ALONG THE WEST COAST WILL EJECT
SEVERAL SHORTWAVES INTO THE REGION. FOR CHRISTMAS EVE/DAY, THE
FOCUS REMAINS ON A POTENTIAL ARCTIC BOUNDARY SPILLING OVER THE
CONTINENTAL DIVIDE. IF THIS "WEDGE" OF ARCTIC AIR MATERIALIZES,
AREAS NEAR MARIAS PASS AND ESSEX COULD EXPERIENCE A SHARP DROP IN
TEMPERATURES AND AN INCREASE IN SNOWFALL RATES. IN ADDITION,
FORECAST MODELS ARE SHOWING ANOTHER SLUG OF MOISTURE WHICH COULD
BRING IMPACTS THE HIGHER ELEVATIONS OF LEMHI COUNTY DURING THE DAY
WEDNESDAY. FOR THE REMAINDER OF WESTERN MONTANA AND NORTH CENTRAL
IDAHO, EXPECT PERIODIC RAIN AND SNOW SHOWERS TO PERSIST THROUGH
THE HOLIDAY.
ON FRIDAY, A ROBUST COLD FRONT IS FORECAST TO SWEEP THROUGH THE REGION.
THIS WILL PROVIDE A MORE DEFINED TRANSITION TO SNOW FOR VALLEY
FLOORS AS SNOW LEVELS LOWER SIGNIFICANTLY BEHIND THE FRONT. BREEZY
CONDITIONS WILL DEVELOP, THOUGH THERE IS STILL SOME MODEL
DIFFERENCE IN HOW STRONG THE WINDS WILL BE. CURRENT MODEL GUIDANCE
SHOWS A 30 TO 50 PERCENT CHANCE OF WINDS EXCEEDING 40 MPH IN THE
VALLEYS OF WESTERN MONTANA, WITH STRONGER SPEEDS POSSIBLE IN THE
TERRAIN.
NEXT WEEKEND: CONDITIONS TREND COOLER WITH PERSISTENT MOUNTAIN SNOW
SHOWERS. WHILE ORGANIZED, HEAVY PRECIPITATION MAY BRIEFLY DIMINISH,
ENSEMBLE GUIDANCE SUGGESTS A POTENTIAL ATMOSPHERIC RIVER EVENT MAY TARGET
THE REGION TOWARD NEW YEAR'S EVE.
AVIATION
VFR CONDITIONS ARE EXPECTED THIS AFTERNOON AS THE
REGION IS GENERALLY IN A LULL IN ORGANIZED PRECIPITATION. PATCHY
FOG AND/OR LOW CLOUDS MAY DEVELOP AT A FEW OF THE TERMINALS THIS
EVENING BEFORE THE NEXT SYSTEM ARRIVES LATE TONIGHT. SNOW AND
FREEZING RAIN WILL BE POSSIBLE ACROSS LEMHI COUNTY AFTER 0800Z
(0100 MST TUESDAY). MOUNTAIN OBSCURATION AND LOWER VISIBILITY IS
EXPECTED THROUGH THE MORNING HOURS. THIS AREA OF PRECIPITATION
WILL SHIFT NORTHWARDS DURING THE DAY TUESDAY AND GENERALLY BE
OVER NORTHWEST MONTANA BY EVENING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY FROM 5 AM TO NOON MST TUESDAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS.
ID...WINTER WEATHER ADVISORY FROM 4 AM TO 11 AM PST TUESDAY FOR
SOUTHERN CLEARWATER MOUNTAINS.
WINTER WEATHER ADVISORY FROM 3 AM TO NOON MST TUESDAY FOR
EASTERN LEMHI COUNTY...WESTERN LEMHI COUNTY.
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