768
FXUS65 KMSO 272054
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
154 PM MST SAT DEC 27 2025
DISCUSSION
KEY MESSAGES:
-LINGERING SNOW BANDS AND GUSTY NORTHEAST WINDS THROUGH THIS
EVENING AS AN ARCTIC COLD FRONT CROSSES THE CONTINENTAL DIVIDE,
IN NORTHWEST MONTANA
-MUCH COLDER TEMPERATURES SUNDAY MORNING, WITH MANY VALLEY
LOCATIONS DROPPING INTO THE SINGLE DIGITS TO LOW TEENS.
-BUILDING RIDGE (EARLY NEXT WEEK): COLD AND MUCH DRIER CONDITIONS
STARTING SUNDAY. POTENTIAL FOR FOG AND LOW STRATUS TO DEVELOP.
THE ARCTIC AIRMASS CONTINUES ITS WESTWARD PROGRESSION ACROSS THE
CONTINENTAL DIVIDE THIS AFTERNOON. SURFACE OBSERVATIONS AS OF NOON
PLACE THE FRONT GENERALLY ALONG THE HIGHWAY 93 CORRIDOR FROM
EUREKA THROUGH KALISPELL. STRONG POST-FRONTAL NORTHEAST WINDS WILL
GUST UP TO 40 MPH IN GAP-FLOW PRONE AREAS SUCH AS BADROCK CANYON.
RAPIDLY FALLING TEMPERATURES BEHIND THE FRONT WILL LEAD TO A HIGH
PROBABILITY OF "FLASH FREEZE" CONDITIONS ON PREVIOUSLY TREATED OR
WET SURFACES ACROSS NORTHWEST MONTANA.
FRONTAL FORCING AND MODEST INSTABILITY ARE CURRENTLY SUPPORTING THE
DEVELOPMENT OF MESOSCALE SNOW BANDS OVER WESTERN MONTANA. WHILE
RESIDENCE TIME FOR THESE BANDS WILL BE LIMITED, HIGH-RESOLUTION
ENSEMBLES SUGGEST SNOWFALL RATES COULD BRIEFLY EXCEED 0.5"/HR
WITHIN THE MOST INTENSE FEATURES.
ATTENTION SHIFTS TONIGHT TO LAKE EFFECT SNOW POTENTIAL OFF FLATHEAD
LAKE, PARTICULARLY ON SOUTHERN AND EASTERN SHORES. HIGH RESOLUTION
MODELS SHOW A ROUGHLY 30 PERCENT CHANCE OF THIS OCCURRING BY
SUNDAY MORNING, WHICH MAY LEAD TO SOME LOCALIZED SNOWFALL ALONG
HIGHWAY 35.
BY SUNDAY MORNING, SOME OF THE COLDEST TEMPERATURES OF THIS WINTER
ARE ANTICIPATED, DROPPING INTO THE SINGLE DIGITS TO BELOW ZERO IN
MANY WESTERN MONTANA VALLEYS AND LOWER 20S TO TEENS FOR EVEN THE
LOWEST VALLEYS OF NORTH CENTRAL IDAHO. LOCATIONS ALONG THE
CONTINENTAL DIVIDE, SUCH AS BUTTE AND SEELEY LAKE HAVE A ROUGHLY
50 PERCENT CHANCE OF SEEING SUBZERO TEMPERATURES.
BY MONDAY, AN UPPER-LEVEL RIDGE BEGINS TO MIGRATE INLAND, TRANSITIONING
THE REGION FROM CYCLONIC NORTHWEST FLOW TO A HIGH-AMPLITUDE RIDGE
AXIS BY MIDWEEK. THIS SYNOPTIC SETUP IS A CLASSIC SIGNAL FOR
STRONG SUBSIDENCE INVERSIONS AND THE DEVELOPMENT OF VALLEY COLD
POOLS.
-TEMPERATURE BIAS: CURRENT MAX TEMPERATURES VALUES ARE LIKELY
TOO WARM FOR VALLEY FLOORS, ESPECIALLY BY TUESDAY/WEDNESDAY
NEXT WEEK. THIS IS A TRICKY FORECAST DUE TO THE COMPLEXITY OF
COLD POOLS AND INVERSIONS AND WILL BE MONITORED BY FUTURE
SHIFTS FOR UPDATES.
-FOG/STRATUS: EXPECT INCREASING COVERAGE OF FREEZING FOG AND LOW
STRATUS WITHIN THE STAGNANT VALLEYS OF WESTERN MONTANA AND
NORTH CENTRAL IDAHO MONDAY NIGHT THROUGH THURSDAY.
MODEL CLUSTERS REMAIN IN GOOD AGREEMENT REGARDING A BREAKDOWN OF THE
RIDGE LATE FRIDAY AS A PACIFIC TROUGH APPROACHES. THERE ARE STILL
SOME TIMING AND STRENGTH DIFFERENCES IN THIS TROUGH, BUT A RETURN
TO A MORE ACTIVE PATTERN IS EXPECTED.
-PRECIPITATION TYPE: THERE IS CONCERN FOR A WINTRY MIX DURING
THE ONSET OF THIS SYSTEM. STRONG VALLEY INVERSIONS MAY PROVE
DIFFICULT TO ERODE, POTENTIALLY TRAPPING SUB-FREEZING AIR AT
THE SURFACE WHILE A WARM NOSE DEVELOPS ALOFT. THIS TRANSITION
PERIOD WILL NEED TO BE MONITORED CLOSELY FOR POTENTIAL HEADLINES
AS THE EVENT APPROACHES.
AVIATION
THE WESTWARD PUSH OF THE ARCTIC FRONT WILL CONTINUE
TO DEGRADE FLIGHT CATEGORIES ACROSS WESTERN MONTANA TERMINALS
THROUGH THIS EVENING, WITH KGPI CURRENTLY EXPERIENCING THE LEADING
EDGE OF THE AIRMASS. PRIMARY CONCERNS INCLUDE IFR/LIFR CONDITIONS
WITHIN MESOSCALE SNOW BANDS WHERE SNOWFALL RATES COULD EXCEED
0.5"/HR, LEADING TO RAPID ACCUMULATIONS ON RUNWAYS AND SIGNIFICANT
REDUCTIONS IN VISIBILITY. STRONG POST-FRONTAL NORTHEASTERLY WINDS
WILL CREATE LOW-LEVEL WIND SHEAR AND MECHANICAL TURBULENCE,
PARTICULARLY NEAR MOUNTAIN PASSES AND GAP-FLOW AREAS LIKE BADROCK
CANYON, WITH GUSTS TO 35 KT. FURTHERMORE, THE SHARP DROP IN
TEMPERATURES POSES A HIGH RISK FOR "FLASH FREEZE" ON TAXIWAYS AND
RUNWAYS THAT REMAIN WET FROM PREVIOUS PRECIPITATION. PRECIPITATION
WILL DECREASE THIS EVENING, ALONG WITH WINDS AND CLOUD COVER.
OVERNIGHT, LAKE EFFECT SNOW POTENTIAL OFF FLATHEAD LAKE MAY
INTRODUCE LOCALIZED SUB-VFR CEILINGS AND VISIBILITIES TO THE SOUTH
AND EAST OF THE LAKE.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY UNTIL 8 PM MST THIS EVENING FOR
BITTERROOT/SAPPHIRE MOUNTAINS...BUTTE/BLACKFOOT REGION...
FLATHEAD/MISSION VALLEYS...POTOMAC/SEELEY LAKE REGION.
WINTER WEATHER ADVISORY UNTIL 5 PM MST THIS AFTERNOON FOR
MISSOULA/BITTERROOT VALLEYS...WEST GLACIER REGION.
ID...WINTER WEATHER ADVISORY UNTIL 8 PM MST /7 PM PST/ THIS EVENING
FOR EASTERN LEMHI COUNTY...SOUTHERN CLEARWATER MOUNTAINS...
WESTERN LEMHI COUNTY.
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