947
FXUS65 KMSO 301006
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
406 AM MDT THU OCT 30 2025
DISCUSSION
KEY MESSAGES:
- HIGH PRESSURE, WEAK DAYTIME TEMPERATURE INVERSIONS THURS-FRI
- BREEZY AND PERIODIC SHOWERS, LIGHT MOUNTAIN SNOW, SAT-SUN
- ACTIVE JET STREAM, SHOWERY AND SEASONALLY MILD NEXT WEEK
HIGH PRESSURE WILL BE THE DOMINANT WEATHER FEATURE OVER THE NORTHERN
ROCKIES THROUGH FRIDAY (HALLOWEEN). THE GRADUAL SEASONAL LOWERING
OF THE SUN ANGLE, COMBINED WITH PASSING CLOUDS, WILL CREATE WEAK
DAYTIME VALLEY TEMPERATURE INVERSIONS (MAYBE MORE LIKE ISOTHERMAL
TO RIDGETOPS) DURING THIS TIME. AS THE HIGH PRESSURE RIDGE AXIS
MOVES OVERHEAD FRIDAY MORNING, PATCHY FOG WILL SHOW UP,
PARTICULARLY ACROSS NORTHWEST MONTANA VALLEYS AND ALONG RIVER
BOTTOMS.
A SURGE OF PACIFIC MOISTURE (AKA, BRIEF ATMOSPHERIC RIVER),
ACCOMPANIED BY A STRONG JET STREAM ALOFT, WILL ARRIVE ACROSS THE
NORTHERN ROCKIES ON SATURDAY AND CONTINUE INTO SUNDAY. WINDS OVER
THE RIDGETOPS NEAR AND ALONG THE CONTINENTAL DIVIDE ARE ANTICIPATED
TO EXCEED 40 MPH AT TIMES, PARTICULARLY OVERNIGHT SATURDAY INTO
SUNDAY MORNING. TEMPERATURES WILL BE RELATIVELY MILD FOR LATE
OCTOBER, HOWEVER A BRIEF REDUCTION IN SNOW LEVELS PROVIDES A LOW
PROBABILITY ICE/SNOW IMPACT FOR AREA MOUNTAIN PASSES DURING SUNDAY
EVENING.
A STRONG JET STREAM IS ANTICIPATED TO CONTINUE BEING PRESENT OVER
THE NORTHERN ROCKIES FOR MUCH OF NEXT WEEK, WITH OCCASIONAL GUSTY
WINDS AND SHOWER ACTIVITY. THE PERSISTENCE OF HIGH PRESSURE OVER THE
WESTERN US MEANS THAT ANY SNOW/ICE IMPACTS WILL BE CONFINED TO ABOVE
MOUNTAIN PASSES FOR MOST OF THIS TIME (AND MAINLY OUTSIDE OF
DAYLIGHT PERIODS).
AVIATION
LOW PROBABILITY OF SIGNIFICANT AVIATION RELATED IMPACTS
ACROSS NORTHERN ROCKIES AIR SPACE THROUGH 31/1800Z, AS HIGH PRESSURE
MOVES OVERHEAD. SURFACE WINDS WILL GENERALLY BE UNDER 15 KTS DURING
THIS TIME, WITH VARIABLE MID-LEVEL CLOUDS/CEILINGS. THERE IS A LOW
PROBABILITY OF BRIEF VALLEY FOG/STRATUS FOR NORTHWEST MONTANA
TERMINALS AROUND 31/1200Z, INCLUDING KGPI AND KMSO.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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