640
FXUS65 KMSO 151918
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
118 PM MDT SUN MAR 15 2026
DISCUSSION
KEY MESSAGES:
- A WARM FRONT WILL BRING ACCUMULATING SNOW TONIGHT THROUGH
MONDAY MORNING. EXPECT GENERALLY ONE HALF TO 3 INCHES IN THE
VALLEYS, BUT IT IS COMMON FOR THESE TYPES OF WEATHER SYSTEMS TO
PRODUCE HIGHER AMOUNTS IN FAVORED LOCATIONS. A WINTRY MIX IS
ALSO POSSIBLE.
- A STRONG RIDGE OF HIGH PRESSURE WILL BUILD LATER THIS WEEK,
SENDING TEMPERATURES SOARING 15 TO 20 DEGREES ABOVE NORMAL BY
FRIDAY.
- THE RAPID LATE-WEEK WARMING WILL QUICKLY MELT THE FRESH VALLEY
SNOW, WHICH MAY LEAD TO URBAN RUNOFF ISSUES AND PONDING OF
WATER IN LOW-LYING AREAS AND POORLY DRAINED STREETS.
COLDER AIR IS CURRENTLY IN PLACE ACROSS THE REGION. WHILE SOME
MODELS SUGGEST TEMPERATURES WILL WARM UP QUICKLY, FRESH SNOW COVER
MEANS THAT WARMING WILL LIKELY BE REDUCED IN MOST PLACES
AS A WARM FRONT PUSHES INTO THE REGION LATE THIS EVENING, IT WILL
LIFT ABUNDANT MOISTURE UP AND OVER OUR EXISTING COLD, DRY
AIRMASS. AS PRECIPITATION BEGINS, EVAPORATIONAL COOLING WILL
QUICKLY LOCK IN FREEZING TEMPERATURES FOR THE VALLEYS. COMBINED
WITH NORTHWESTERLY FLOW ALOFT, THIS CREATES A CLASSIC SETUP FOR
ACCUMULATING SNOW IN THE NARROW VALLEYS OF NORTH-CENTRAL IDAHO AND
WEST-CENTRAL MONTANA, INCLUDING MISSOULA.
STANDARD MODEL GUIDANCE TENDS TO UNDER-FORECAST SNOW AMOUNTS IN
THESE SETUPS, GENERALLY SHOWING LESS THAN AN INCH. HOWEVER, GIVEN
THE ENVIRONMENT, HIGHER AMOUNTS OF 2 TO 4 INCHES ARE ENTIRELY
POSSIBLE. COMMUTERS SHOULD PLAN FOR WINTER DRIVING CONDITIONS AND
EXTRA TRAVEL TIME MONDAY MORNING, AS ROADS WILL LIKELY BE SNOW-
COVERED AND SLICK. ADDITIONALLY, AS SNOW LEVELS RAPIDLY RISE ON
MONDAY, POCKETS OF FREEZING RAIN ARE POSSIBLE, WHICH WOULD FURTHER
COMPLICATE TRAVEL.
FURTHER NORTH TOWARD KALISPELL, THE FORECAST IS TRICKIER. THE
DEEPEST MOISTURE IS EXPECTED TO REMAIN FURTHER SOUTH. WHILE THE
FLATHEAD VALLEY WILL LIKELY SEE SOME SNOW, AMOUNTS SHOULD BE
LIGHT, GENERALLY AN INCH OR LESS, UNLESS THE MOISTURE SHIELD
DRIFTS FURTHER NORTH THAN ANTICIPATED.
BEHIND MONDAY'S SYSTEM, A SIGNIFICANT PATTERN CHANGE TAKES HOLD
AS A STRONG RIDGE OF HIGH PRESSURE BUILDS ACROSS THE WESTERN US.
WHILE THE NORTHERN ROCKIES WILL SIT ON THE NORTHERN PERIPHERY OF
THIS RIDGE, ATMOSPHERIC HEIGHTS WILL CLIMB WELL ABOVE AVERAGE,
DRIVING A MAJOR WARMING TREND.
BY THURSDAY AND FRIDAY, TEMPERATURES WILL RUN 15 TO 20 DEGREES
ABOVE NORMAL, PUSHING AFTERNOON HIGHS INTO THE UPPER 50S TO UPPER
60S FOR MANY VALLEY LOCATIONS. DESPITE THE WARMTH, PACIFIC
MOISTURE WILL CONTINUE TO STREAM INTO NORTHWEST MONTANA. THIS WILL
KEEP SHOWERS IN THE FORECAST FOR THE ENTIRE WEEK, PRIMARILY IN
THE MOUNTAINS, WITH SNOW LEVELS RISING REMARKABLY HIGH TO BETWEEN
7,000 AND 8,000 FEET.
URBAN RUNOFF POTENTIAL: WITH THIS RAPID TRANSITION FROM FREEZING
TEMPERATURES AND FRESH SNOW TO WELL- ABOVE-AVERAGE WARMTH, THE
NEWLY DEPOSITED VALLEY SNOWPACK WILL MELT RAPIDLY. EXPECT
LOCALIZED PONDING OF WATER IN LOW-LYING AREAS, POOR DRAINAGE
ZONES, AND URBAN ROADWAYS FROM TUESDAY INTO THE WEEKEND.
NEXT WEEKEND:
THE RIDGE AXIS IS EXPECTED TO SHIFT EASTWARD BY SUNDAY, OPENING
THE DOOR FOR THE NEXT PACIFIC TROUGH TO APPROACH FROM THE
NORTHWEST. THIS WILL LIKELY BRING OUR NEXT CHANCE FOR WIDESPREAD
PRECIPITATION AND COOLER TEMPERATURES, THOUGH THE EXACT TIMING
REMAINS UNCERTAIN.
AVIATION
MID AND UPPER-LEVEL CLOUDS WILL BE ON THE INCREASE
THROUGH THE REST OF TODAY AS THE NEXT WEATHER SYSTEM MOVES IN
OVERNIGHT TONIGHT. ALL ELEVATIONS WILL BE COLD ENOUGH FOR LIGHT
SNOW STARTING AFTER 16/0300Z THIS EVENING. LIGHT TO MODERATE SNOW
WILL CONTINUE THROUGH THE NIGHT AND INTO MONDAY MORNING FOR ALL
AVIATION SITES IN WESTERN MONTANA. MID-LEVEL WARMING MAY BE JUST
ENOUGH TO WHERE LIGHT SNOW WILL TRANSITION TO A LIGHT FREEZING
RAIN FOR THE VALLEYS ALONG I-90, ENCOMPASSING KMSO. WHILE THE
CONFIDENCE IS LOW, AT AROUND A 15% PROBABILITY, IT IS STILL WORTH
MENTIONING. VISIBILITY DOWN TO 1SM AND LOW CEILINGS CAN BE
EXPECTED AT LEAST THROUGH 16/1500Z TOMORROW MORNING FOR KMSO, KHRF
AND KBTM. WIDESPREAD MOUNTAIN OBSCURATIONS WILL BE PRESENT MOST
OF THE MONDAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO NOON MDT
MONDAY FOR BITTERROOT/SAPPHIRE MOUNTAINS...LOWER CLARK FORK
REGION.
WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON MDT MONDAY
FOR MISSOULA/BITTERROOT VALLEYS...POTOMAC/SEELEY LAKE
REGION.
ID...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 11 AM PDT
MONDAY FOR SOUTHERN CLEARWATER MOUNTAINS.
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