194
FXUS65 KMSO 130920
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
220 AM MST SAT DEC 13 2025
DISCUSSION
KEY MESSAGES:
- DENSE FOG AND LOW CLOUDS IN VALLEYS EACH MORNING FROM TODAY
THROUGH MONDAY
- A WEAK TO MODERATE ATMOSPHERIC RIVER ARRIVING MONDAY THROUGH
WEDNESDAY
- COLD FRONT ON WEDNESDAY WILL DROP SNOW LEVELS TO VALLEY FLOORS
RADAR RETURNS EARLY THIS MORNING INDICATE LIGHT SHOWERS ALONG THE
CONTINENTAL DIVIDE IN NORTHWEST MONTANA. VERY COLD AIR EAST OF
THE DIVIDE COULD SPILL OVER IN THE MARIAS PASS AREA, RESULTING IN
LIGHT ACCUMULATING SNOW ON THE ROAD THROUGH ABOUT MID-MORNING.
OTHERWISE, THE COLDEST TEMPERATURES WILL REMAIN EAST OF THE DIVIDE
TODAY, AND HIGH PRESSURE WILL BUILD OVER THE NORTHERN ROCKIES.
DRY CONDITIONS TODAY AND ON SUNDAY WILL BRING A MUCH NEEDED BREAK
IN WET WEATHER, ESPECIALLY FOR NORTHWEST MONTANA. VALLEY FOG AND
LOW STRATUS CLOUDS WILL DEVELOP EACH MORNING THROUGH MONDAY.
VALLEYS ACROSS THE NORTHERN ROCKIES COULD SEE DENSE FOG AT TIMES.
ON SUNDAY NIGHT INTO MONDAY, LOW PRESSURE OVER THE GULF OF ALASKA
AND HIGH PRESSURE OFF THE COAST OF CALIFORNIA WILL WORK TOGETHER
TO SEND A PLUME OF PACIFIC MOISTURE ONSHORE AND INTO THE NORTHERN
ROCKIES. THIS PROLONGED ATMOSPHERIC RIVER EVENT WILL BRING MORE
RAIN/SNOW TO THE REGION THROUGHOUT THE WEEK. MULTI-DAY
PRECIPITATION TOTALS ARE NOT AS IMPRESSIVE AS THE MOST RECENT
EVENT, HOWEVER THE FOCUS FOR HEAVIEST PRECIPITATION WILL AGAIN BE
NORTHWEST MONTANA. FOUR DAY TOTALS ENDING ON FRIDAY MORNING WILL
BE ONE TO TWO INCHES OF LIQUID FOR LIBBY AND TROY, WITH THREE TO
FOUR INCHES IN THE CABINETS AND HIGHER TERRAIN ALONG THE IDAHO-
MONTANA BORDER. TUESDAY AND TUESDAY NIGHT WILL BE THE PERIOD OF
HEAVIEST PRECIPITATION. OTHER AREAS THAT SHOULD EXPECT HEAVY
PRECIPITATION ARE THE CLEARWATER, SWAN, MISSION, AND FLATHEAD
RANGES, ALL OF WHICH COULD SEE 1.5 TO 3 INCHES WITH HIGH END
POTENTIAL OF ABOUT 4 INCHES. SNOW LEVELS WILL START OUT QUITE
HIGH, AROUND 7000 FEET ON MONDAY. A SHORTWAVE DISTURBANCE ARRIVING
ON WEDNESDAY WILL BRING AN ASSOCIATED COLD FRONT, DROPPING SNOW
LEVELS TO THE VALLEY FLOORS THROUGH ABOUT THURSDAY. THIS FRONT
WILL BRING STRONG WESTERLY WINDS ON WEDNESDAY.
DUE TO ALREADY SATURATED GROUND, PARTICULARLY IN NORTHWEST MONTANA,
THIS RAINFALL INCREASES THE RISK OF ROCKSLIDES, LANDSLIDES, SHARP
RISES ON STREAMS AND RIVERS, AND MINOR FLOODING. PLEASE CONTINUE
TO MONITOR FORECAST UPDATES AND ACTIVE FLOOD WATCHES AS THIS
SYSTEM APPROACHES.
AVIATION
HIGH PRESSURE WILL BUILD OVER THE NORTHERN ROCKIES
TODAY AND ON SUNDAY, LEADING TO THE DEVELOPMENT OF VALLEY FOG AND
STRATUS EACH MORNING. FOG MAY BECOME DENSE AT TIMES, DECREASING
VISIBILITY DURING MORNING HOURS AT KGPI (KALISPELL) AND POSSIBLY
KMSO (MISSOULA). EXPECT DECREASING CLOUDS AND LIGHT WINDS FOR THE
REMAINDER OF TODAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY UNTIL 5 AM MST EARLY THIS MORNING FOR
WEST GLACIER REGION.
ID...NONE.
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