949
FXUS65 KMSO 281859
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
1159 AM MST SUN DEC 28 2025
DISCUSSION
KEY MESSAGES:
- VERY COLD MORNINGS WILL CONTINUE THROUGH THE FIRST HALF OF THIS
WEEK.
- DEVELOPING INVERSIONS WILL LIKELY LEAD TO FOG, STRATUS AND POOR
AIR QUALITY.
SOME OF THE COLDEST AIR SO FAR THIS WINTER HAS SETTLED OVER
WESTERN MONTANA AND NORTH-CENTRAL IDAHO. MOST AREAS SAW
TEMPERATURES DROP INTO THE SINGLE DIGITS THIS MORNING, WITH
SEVERAL MOUNTAIN VALLEYS FALLING BELOW ZERO. SOME OF THE COLDEST
SPOTS WERE IN NORTH-CENTRAL IDAHO, WHERE TEMPERATURES REACHED
-13°F AT GILMORE SUMMIT AND -11°F IN DIXIE.
AS HIGH PRESSURE STRENGTHENS OVER THE REGION, SO TOO WILL THE
VALLEY INVERSIONS. THIS "LID" ON THE ATMOSPHERE MAKES IT MORE
LIKELY THAT THICK VALLEY FOG AND LOW STRATUS WILL DEVELOP BY
MONDAY AND TUESDAY MORNINGS. THIS STAGNANT AIR WILL ALSO LEAD TO
CONCERNS ABOUT POOR AIR QUALITY THROUGH MIDWEEK. WHILE AFTERNOON
TEMPERATURES WILL RISE SLIGHTLY EACH DAY, THIS MORNING AND MONDAY
MORNING ARE EXPECTED TO BE THE TWO COLDEST DAYS OF THE WEEK.
WE EXPECT THIS STABLE PATTERN TO REMAIN UNTIL AT LEAST FRIDAY,
WHEN A PACIFIC TROUGH MOVES ASHORE. CONFIDENCE IN THE EXACT TIMING
IS CURRENTLY LOW, AS WEATHER MODELS DISAGREE ON WHEN THE HIGH
PRESSURE WILL BREAK DOWN. ABOUT 10% OF MODELS SHOW THE WEATHER
CHANGING AS EARLY AS FRIDAY, WHILE THE MAJORITY SUGGEST THE CHANGE
WILL HAPPEN NEXT WEEKEND OR EARLY NEXT WEEK. WHENEVER THIS SHIFT
OCCURS, THERE IS A RISK OF LIGHT FREEZING RAIN IN THE VALLEYS AS
MOISTURE MOVES OVER THE COLD AIR STILL TRAPPED AT THE SURFACE.
PLEASE STAY TUNED FOR UPDATES AS THE WEEK PROGRESSES.
AVIATION
SOME OF THE COLDEST AIR THIS SEASON HAS SETTLED OVER
THE NORTHERN ROCKIES. WIDESPREAD SINGLE DIGIT TEMPERATURES WERE
OBSERVED, WITH SEVERAL PLACES SEEING BELOW ZERO LOWS IN THE
BROADER VALLEYS ALONG THE CONTINENTAL DIVIDE IN WESTERN MONTANA.
TEMPERATURES WILL BEGIN TO MODERATE AS WE PROGRESS THROUGH THE
WEEK, WITH THIS MORNING AND MONDAY MORNING LIKELY BEING THE TWO
COLDEST MORNINGS. AS THE RIDGE STRENGTHENS, SO TOO WILL THE
VALLEY INVERSIONS. VALLEY STRATUS AND/OR FOG WILL BECOME A CONCERN
BY MONDAY OR TUESDAY MORNING.
AIR STAGNATION
A RIDGE OF HIGH PRESSURE WILL STRENGTHEN OVER
THE NORTHERN ROCKIES EARLY THIS COMING WEEK. THE RIDGE IS EXPECTED
TO REMAIN IN PLACE FOR MOST OF THE WEEK, POTENTIALLY BREAKING DOWN
AS EARLY AS FRIDAY. AIR STAGNATION CONCERNS MAY BE REALIZED BY
TUESDAY OF THIS COMING WEEK.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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