406
FXUS65 KMSO 212128
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
228 PM MST WED JAN 21 2026
DISCUSSION
KEY MESSAGES:
- STRONG VALLEY INVERSIONS AND FOG/STRATUS LINGER INTO THURSDAY,
ESPECIALLY IN NORTH CENTRAL IDAHO.
- COLDEST AIR OF THE WINTER THUS FAR BEGINS TO FILTER INTO THE
REGION THURSDAY THROUGH FRIDAY. COLD WIND CHILLS AROUND 10 BELOW
ZERO IN NORTHWEST MONTANA AND ALONG THE CONTINENTAL DIVIDE
FRIDAY MORNING.
FOG AND LOW CLOUDS REMAIN TRAPPED IN THE VALLEYS OF NORTHWEST
MONTANA AND NORTH CENTRAL IDAHO TODAY. OVERALL WE ANTICIPATE THIS
CLOUD COVER WILL BEGIN TO LIFT OVERNIGHT TONIGHT INTO THURSDAY
MORNING AS A COLDER AIRMASS FROM CANADA BEGINS TO SPILL OVER THE
CONTINENTAL DIVIDE. NORTH CENTRAL IDAHO WILL BE THE LAST TO SEE
CLEARING, MOST LIKELY NOT UNTIL LATER IN THE DAY THURSDAY.
BREEZY NORTHEAST TO EAST WINDS WILL DEVELOP THURSDAY WITH THE
BEGINNING OF THE ARCTIC SPILLOVER, THOUGH NOT OVERLY STRONG WITH
EXPOSED AREAS GENERALLY SEEING WINDS BETWEEN 20 TO 30 MPH THROUGH
THURSDAY. DUE TO THE AIRMASS DROPPING OUT OF CONTINENTAL AREAS IN
CANADA, THERE IS LITTLE MOISTURE FOR THIS FRONT TO WORK WITH, THUS
CONDITIONS WILL BE MAINLY DRY.
MUCH COLDER AIR, THE COLDEST WE HAVE SEEN SO FAR THIS WINTER, WILL
FILTER INTO WESTERN MONTANA AND NORTH CENTRAL IDAHO FRIDAY INTO
SATURDAY. WHILE NOT RECORD-BREAKING COLD BY JANUARY STANDARDS, THE
MILD WINTER WE HAVE HAD OF LATE WILL MAKE THIS FEEL LIKE A
SIGNIFICANT CHANGE. THE COLDEST AIR IS ANTICIPATED ACROSS
NORTHWEST MONTANA AND ALONG THE CONTINENTAL DIVIDE WHERE SINGLE
DIGITS TO EVEN BELOW ZERO TEMPERATURES WILL BE OBSERVED. FALLING
TEMPERATURES WILL OVERLAP WITH WIND LATE THURSDAY NIGHT INTO
FRIDAY MORNING TO PRODUCE WIND CHILLS AS LOW AS -5 TO -15 DEGREES
BELOW ZERO. WINDS WILL RELAX DURING THE DAY FRIDAY, WITH MANY
VALLEYS LIKELY SEEING THE COLDEST TEMPERATURES SATURDAY MORNING,
DEPENDING ON CLOUD COVER.
TEMPERATURES WILL SLOWLY MODERATE SUNDAY INTO EARLY NEXT WEEK.
FORECAST MODELS CONTINUE TO SHOW A WEAK DISTURBANCE OVERRUNNING
THE COLDER AIR IN PLACE IN THE MONDAY/TUESDAY TIMEFRAME. SEVENTY-
FIVE PERCENT OF MODELS SHOW THIS AS A VERY LIGHT PRECIPITATION
EVENT WITH MINIMAL ACCUMULATIONS. HOWEVER, AROUND 25 PERCENT SHOW
SOMEWHAT HIGHER AMOUNTS (2 TO 4 INCHES SNOWFALL), WHICH COULD
LEAD TO SOME MINOR IMPACTS DUE TO ACCUMULATING SNOW, ESPECIALLY
OVER MOUNTAIN PASSES ALONG THE IDAHO/WESTERN MONTANA BORDER.
EIGHTY PERCENT OF FORECAST MODELS SHOW THE RIDGE OF HIGH PRESSURE
BUILDING BACK OVER THE REGION BY WEDNESDAY NEXT WEEK, ALLOWING
STRONG INVERSIONS TO REDEVELOP WITH THE THREAT OF FOG AND/OR LOW
STRATUS.
AVIATION
LOW STRATUS AND POCKETS OF FOG REMAIN LOCKED IN
ACROSS NORTHWEST MONTANA AND THE LOWER VALLEYS OF NORTH CENTRAL
IDAHO. OBSCURED TERRAIN WILL BE THE MAIN CONCERN WITH THE LOWER
CLOUD DECK. AS AN ARCTIC AIRMASS DROPS SOUTH OUT OF CANADA, IT
WILL BEGIN TO INCREASE A NORTHEASTERLY PRESSURE GRADIENT, FIRST
ACROSS NORTHWEST MONTANA AFTER 22/1200Z AND THEN INTO THE REST OF
WESTERN MONTANA BETWEEN 22/1500Z TO 22/1800Z. WIND GUSTING UP TO
25KTS IN EXPOSED LOCATIONS WILL BE POSSIBLE, INCLUDING AT KGPI.
THIS INCREASED WIND SHOULD HELP RAISE THE CLOUD DECK, OTHER THAN
PERHAPS THROUGH NORTH CENTRAL IDAHO, WHERE THE EASTERLY GRADIENT
WON'T REALLY MATERIALIZE UNTIL AFTER 23/0000Z. THIS AIR MASS IS
RELATIVELY DRY AND THUS WIDESPREAD PRECIPITATION IS NOT
ANTICIPATED.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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