775
FXUS65 KMSO 242004
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
104 PM MST WED DEC 24 2025
DISCUSSION
KEY MESSAGES:
- CHRISTMAS EVE TRAVEL: STUBBORN VALLEY FOG LIFTS THIS AFTERNOON,
TRANSITIONING TO WIDESPREAD VALLEY RAIN AND MOUNTAIN SNOW BY
EVENING.
- FRIDAY IMPACT (WIND): A POTENT COLD FRONT ARRIVES LATE FRIDAY.
THE RISK OF DOWNED TREES AND POWER OUTAGES IS HIGH DUE TO
SATURATED SOILS, DESPITE ONLY MODERATE WIND SPEEDS (GUSTS 35-45
MPH).
- SATURDAY IMPACT (COLD): AN ARCTIC AIRMASS SPILLS OVER THE
DIVIDE SATURDAY. FLASH/RAPID FREEZE CONDITIONS ARE POSSIBLE ON
WET ROADWAYS AS TEMPERATURES PLUMMET, PARTICULARLY IN
NORTHWEST MONTANA.
THROUGH CHRISTMAS DAY: EXTENSIVE CLOUD COVER CONTINUES TO STREAM
IN FROM THE SOUTH AND WEST THIS AFTERNOON, MARKING THE LEADING
EDGE OF AN ATMOSPHERIC RIVER AFFECTING CENTRAL CALIFORNIA AND THE
GREAT BASIN. VALLEY FOG HAS BEEN PERSISTENT AND STUBBORN TO
MECHANICAL MIXING THIS MORNING DUE TO A NEARLY ISOTHERMAL VERTICAL
PROFILE (WITH TEMPERATURES EVEN SLIGHTLY WARMING WITH HEIGHT UP
TO 8,000 FT MSL). WE ANTICIPATE THE FOG WILL SLOWLY MIX OUT WITH
THE ONSET OF INCREASING SOUTHERLY SURFACE WINDS AND PRECIPITATION
LATER THIS AFTERNOON.
WITH 700MB TEMPERATURES RISING NEAR, OR SLIGHTLY ABOVE
FREEZING, MIXED PRECIPITATION TYPES ARE LIKELY (LEANING TOWARD
RAIN) AHEAD OF A WEAK COLD FRONT EXPECTED NEAR/AFTER MIDNIGHT.
• FREEZING RAIN NOTE: WHILE NOT WIDESPREAD, THE MOST SHELTERED
VALLEYS (ESPECIALLY NEAR AND EAST OF THE CONTINENTAL DIVIDE WHERE
COLD POOLS ARE STUBBORN TO ERODE) MAY EXPERIENCE A BRIEF PERIOD
OF FREEZING RAIN AT ONSET.
• TRANSITION: COOLING ALOFT, ALONG AND BEHIND THE FRONT, MAY
ALLOW FOR A BRIEF CHANGEOVER TO SNOW CLOSER TO VALLEY FLOORS,
ESPECIALLY UNDER POCKETS OF HEAVIER PRECIPITATION RATES.
CHRISTMAS MORNING – FRIDAY MORNING: THE AXIS OF MAXIMUM MOISTURE
WILL LIKELY STAY TO OUR SOUTH, GUIDING THE HEAVIEST PRECIPITATION
EAST BEFORE HYDROLOGICAL CONCERNING LEVELS REACH OUR AREA. DRIER
AIR MOVES IN FROM THE WEST CHRISTMAS MORNING, THOUGH VALLEY FOG
AND LOW STRATUS MAY RELOAD AND PERSIST THROUGH MIDDAY. BY THURSDAY
NIGHT, MOISTURE STREAMING AHEAD OF A LOW APPROACHING THE OREGON
COAST WILL INTRODUCE NEW CHANCES FOR SHOWERS AND PASS-LEVEL SNOW.
FRIDAY AFTERNOON & NIGHT (HIGHEST IMPACT WINDOW): A POTENT COLD
FRONT ARRIVES FROM THE WEST-NORTHWEST LATE FRIDAY. WE ARE WATCHING
THIS PERIOD CLOSELY FOR WIDESPREAD IMPACTS DUE TO SNOW AND WIND.
• WIND SPEEDS: VALLEYS MAY SEE SOUTHWESTERLY GUSTS
TO 35-40 MPH, WITH MOUNTAINS/RIDGES GUSTING 50-65+ MPH.
• IMPACT WARNING: DUE TO MULTIPLE RECENT WIND EVENTS, PROLONGED
SOIL SATURATION, AND WEAKENED ROOT SYSTEMS, THE RISK FOR DOWNED
TREES AND POWER OUTAGES IS UNUSUALLY HIGH FOR A WIND EVENT OF THIS
MODEST STRENGTH.
SATURDAY (ARCTIC INTRUSION): FOLLOWING THE INITIAL FRONT FROM THE
WEST, MUCH COLDER AIR (NEAR 0°F) WILL SLIDE SOUTH, EAST OF THE
DIVIDE, EVENTUALLY SEEPING WESTWARD ACROSS AREAS, SUCH AS MARIAS
PASS, INTO NORTHWESTERN MONTANA THROUGHOUT SATURDAY.
• WINDS: EXPECT A SHARP UPTICK/CHANGE IN DIRECTION TO
NORTH/NORTHEAST WINDS, ACCELERATING THROUGH PRONE CANYONS AND
DOWNSLOPE FOOTHILLS (SWAN, FLATHEAD, BAD ROCK).
• FLASH FREEZE: WITH THE ARRIVAL OF MUCH COLDER AIR OVER WET OR
SLUSHY SURFACES, FLASH/RAPID FREEZE CONDITIONS ARE POSSIBLE IN
AREAS WHERE RECENT PRECIPITATION HAS FALLEN WITH SNOW SHOWERS
PERSISTING THROUGH LATE SATURDAY.
• THE SOUTH AND WESTWARD EXTENT: OF THIS ARCTIC AIR IS STILL A
DETAIL THAT NEEDS FURTHER REFINEMENT WITH TIME AND FUTURE MODEL
GUIDANCE.
SUNDAY INTO NEXT WEEK: A DOMINANT RIDGE OF HIGH PRESSURE SETS UP
ACROSS THE PACIFIC NORTHWEST, BRINGING OVERALL CALMER AND DRIER
CONDITIONS. HOWEVER, WITH THE RIDGE AXIS POSITIONED TO OUR WEST,
THE REGION REMAINS IN COOL NORTHWESTERLY FLOW. THIS MAY ALLOW
MINOR DISTURBANCES TO SNEAK OVER THE TOP OF THE RIDGE, KEEPING
VERY SLIGHT POTENTIAL FOR SCATTERED PRECIPITATION IN THE FORECAST
AT THIS TIME THROUGH THE FIRST HALF OF THE WEEK.
AVIATION
LIFR/IFR WEATHER CONDITIONS INCLUDING VALLEY FOG AND
STRATUS WILL GRADUALLY LIFT TO MVFR/VFR THIS AFTERNOON AS
SOUTHERLY WINDS INCREASE AHEAD OF THE INCOMING SYSTEM. WIDESPREAD
MOUNTAIN OBSCURATIONS RETURN THIS EVENING (00Z-04Z) AS
PRECIPITATION (MOSTLY RAIN OR A RAIN/SNOW MIX) OVERSPREADS THE
REGION, LOWERING CEILINGS AND VISIBILITY BACK TO MVFR/IFR. BEHIND
THE FRONTAL PASSAGE TONIGHT, ABUNDANT LOW-LEVEL MOISTURE AND
CALMING WINDS WILL LIKELY CAUSE TERMINALS TO RAPIDLY DETERIORATE
BACK TO LIFR/IFR IN DENSE FOG AND LOW STRATUS, PERSISTING THROUGH
CHRISTMAS MORNING.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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