685
FXUS65 KMSO 231739
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1039 AM MST TUE DEC 23 2025
UPDATE
WINTER WEATHER ADVISORY ISSUED FOR THE SEELEY LAKE AND
POTOMAC REGION THROUGH 2:00PM MST FOR SNOW AND FREEZING RAIN
IMPACTS.
DISCUSSION
LIGHT MOUNTAIN SNOW AND VALLEY SNOW/FREEZING RAIN THIS MORNING
REMAINS THE PRIMARY FORECAST CONCERN AS A SOUTH-TO-NORTH MOISTURE
SURGE OVERRUNS A SHALLOW, COLD AIR MASS TRAPPED WITHIN MOUNTAIN
VALLEYS OF WESTERN MONTANA. SURFACE OBSERVATIONS CURRENTLY SHOW A
STUBBORN LAYER OF AIR IN THE UPPER 20S TO LOW 30S ACROSS THE
MISSOULA AND BITTERROOT VALLEYS, WHICH IS FACILITATING FREEZING
RAIN AND LIGHT SNOW. WHILE THE BITTERROOT VALLEY IS SEEING THE
MOST CONSISTENT ICE GLAZE, RADAR AND SATELLITE TRENDS INDICATE
PRECIPITATION WILL SPREAD TOWARDS THE I-90 AND HIGHWAY 200
CORRIDORS WITHIN THE SEELEY LAKE AND POTOMAC AREAS. GIVEN THAT
CURRENT TEMPERATURES IN THESE AREAS ARE HOLDING IN THE MID-20S,
THE POTENTIAL FOR ICE ACCUMULATION AND SNOW-COVERED ROADS HAS
NECESSITATED THE EXPANSION OF THE WINTER WEATHER ADVISORY FOR
THESE ZONES THROUGH 2:00 PM MST. LOOKING AHEAD THROUGH THE
AFTERNOON, A GRADUAL RISE IN SURFACE TEMPERATURES INTO THE MID TO
UPPER 30S SHOULD EVENTUALLY TRANSITION MOST VALLEY PRECIPITATION
TO RAIN OR A WET RAIN/SNOW MIX.
AVIATION
FREEZING RAIN WILL CONTINUE TO IMPACT KMSO AND KHRF
THROUGH LATE MORNING/EARLY AFTERNOON AS TEMPERATURES HOLD NEAR
30-32F AND LIGHT PRECIPITATION SPREADS FROM SOUTH TO NORTH. THIS
AREA OF PRECIPITATION WILL SHIFT NORTHWARDS DURING THE DAY AND
GENERALLY BE OVER NORTHWEST MONTANA BY EVENING.
PREV DISCUSSION
/ISSUED 212 AM MST TUE DEC 23 2025/
DISCUSSION...
KEY MESSAGES:
- WINTRY MIX TODAY: A PULSE OF MOISTURE MOVING FROM SOUTH TO
NORTH WILL CREATE SLICK TRAVEL CONDITIONS TODAY. EXPECT A MESSY
TRANSITION OF SNOW AND FREEZING RAIN IN THE VALLEYS THROUGH
THE AFTERNOON.
- CHRISTMAS ARCTIC WEDGE: FORECASTERS ARE CLOSELY WATCHING FOR A
SHALLOW PUSH OF ARCTIC AIR INTO NORTHWEST MONTANA ON CHRISTMAS
EVE. THIS COULD LEAD TO A SHARP TEMPERATURE DROP AND LOCALIZED
HEAVY SNOW NEAR THE DIVIDE.
- COLD FRONT FRIDAY: A ROBUST COLD FRONT REMAINS ON TRACK FOR
FRIDAY, WHICH WILL BRING A DEFINITIVE CHANGEOVER FROM RAIN TO
SNOW FOR ALL VALLEY FLOORS AND GUSTY WINDS.
A COMPLEX AND ACTIVE WEATHER PATTERN CONTINUES AS MOIST PACIFIC
AIR OVERRIDES STUBBORN COOL AIR TRAPPED IN OUR MOUNTAIN VALLEYS.
THIS SETUP REMAINS THE PRIMARY CHALLENGE FOR THE EARLY PART OF THE
WEEK, WITH A BROADER SHIFT TOWARD A COLDER, MORE WINTRY REGIME
ARRIVING JUST IN TIME FOR THE HOLIDAY WEEKEND.
TODAY THROUGH WEDNESDAY: THE NEXT WAVE OF PRECIPITATION IS
ADVANCING INTO THE REGION THIS MORNING. WE ARE SEEING THERMAL
PROFILES THAT FAVOR SNOW AND FREEZING RAIN RATHER THAN A CLEAN
SWITCH TO RAIN THIS MORNING. WINTER WEATHER ADVISORIES ARE IN
EFFECT FOR PARTS OF LEMHI COUNTY, THE CLEARWATER MOUNTAINS, THE
BITTERROOT/SAPPHIRE RANGE, AND MISSOULA/BITTERROOT VALLEYS THROUGH
MIDDAY FOR LOW ELEVATION MIXED PRECIPITATION AND MOUNTAIN PASS
LEVEL SNOW. ELSEWHERE, ISOLATED SLICK SPOTS ARE EXPECTED WITH A
WINTRY MIX. THE DIFFERENCE BETWEEN WET AND ICY ROAD SURFACES WILL
BE NARROW.
BY TONIGHT, PRECIPITATION BECOMES FOCUSED TO NORTHWEST MONTANA.
WHILE MOST VALLEYS MAY SEE A BRIEF PERIOD OF RAIN OR A RAIN/SNOW
MIX AS THE AIRMASS MODIFIES, THE FAR NORTHERN TIER NEAR MARIAS
PASS AND ESSEX NEEDS TO BE MONITORED. THERE IS A PERSISTENT SIGNAL
THAT A "WEDGE" OF ARCTIC AIR COULD SPILL OVER THE CONTINENTAL
DIVIDE, WHICH WOULD LEAD TO MUCH COLDER TEMPERATURES WITH EITHER
INCREASE POTENTIAL FOR SNOW OR FREEZING RAIN FOR THOSE SPECIFIC
AREAS WHILE THE REST OF THE REGION REMAINS RELATIVELY MILD.
THURSDAY THROUGH SUNDAY: THE WEATHER REMAINS UNSETTLED THROUGH
CHRISTMAS DAY WITH SCATTERED MOUNTAIN SNOW AND VALLEY RAIN/SNOW
SHOWERS. HOPES FOR A WHITE CHRISTMAS ARE SLIM FOR THE VALLEYS,
WITH ONLY A 5% CHANCE FOR A HALF-INCH OF SNOW. THIS WOULD MARK A
RARE THIRD SNOW-FREE CHRISTMAS ON RECORD FOR LOCATIONS LIKE
KALISPELL AND MISSOULA.
CHANGES OCCURS ON FRIDAY. A STRONG PACIFIC COLD FRONT IS FORECAST
TO SWEEP THROUGH THE NORTHERN ROCKIES. THIS WILL:
CRASH SNOW LEVELS TO THE VALLEY FLOORS, ENDING THE RAIN/SNOW MIX
AND TRANSITIONING EVERYTHING TO SNOW.
INCREASE WINDS, WITH GUSTY CONDITIONS LIKELY ALONG THE FRONT.
COOLDOWN: TEMPERATURES WILL TREND BACK TOWARD SEASONAL NORMALS
FOR THE WEEKEND.
LOOKING AHEAD TOWARD THE NEW YEAR, ENSEMBLE GUIDANCE IS ALREADY
HINTING AT A POTENTIAL ATMOSPHERIC RIVER EVENT. THIS COULD BRING
ANOTHER ROUND OF SIGNIFICANT MOISTURE AND WINDIER CONDITIONS TO
END THE YEAR, THOUGH DETAILS ON THE EXACT TRACK REMAIN UNCERTAIN.
AVIATION...BRIEF SHOWERS IS NORTH-CENTRAL IDAHO INTO WEST-CENTRAL
MONTANA WILL CONTINUE TO LOWER CEILINGS AND REDUCE VISIBILITY AT
TIMES THROUGH AROUND SUNRISE. THE NEXT SYSTEM ARRIVES FROM THE
SOUTH THIS MORNING. EXPECT CONDITIONS TO DETERIORATE TO MVFR/IFR
THIS MORNING AS PRECIPITATION OVERSPREADS THE REGION, AND MOUNTAIN
OBSCURATION WILL BE WIDESPREAD. THE PRIMARY CONCERN FOR TERMINALS
LIKE KMSO, KHRF, AND KSMN WILL BE A WINTRY MIX OF SNOW AND
FREEZING RAIN THROUGH 18Z. THIS AREA OF PRECIPITATION WILL SHIFT
NORTHWARDS DURING THE DAY AND GENERALLY BE OVER NORTHWEST MONTANA
BY EVENING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY UNTIL NOON MST TODAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS...MISSOULA/BITTERROOT VALLEYS.
WINTER WEATHER ADVISORY UNTIL 2 PM MST THIS AFTERNOON FOR
POTOMAC/SEELEY LAKE REGION.
ID...WINTER WEATHER ADVISORY UNTIL NOON MST /11 AM PST/ TODAY FOR
EASTERN LEMHI COUNTY...SOUTHERN CLEARWATER MOUNTAINS...
WESTERN LEMHI COUNTY.
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