509
FXUS65 KMSO 162114
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
214 PM MST SUN FEB 16 2025
DISCUSSION
KEY MESSAGES:
- STEADY SNOW HAS BEGUN TO FALL ACROSS MUCH OF THE NORTHERN
ROCKIES.
- HEAVIER SNOWFALL IS EXPECTED LATER TONIGHT AND CONTINUING
THROUGH MONDAY NIGHT, SIGNIFICANTLY IMPACTING TRAVEL ACROSS THE
REGION.
OVERALL THE FORECAST IS PLAYING OUT VERY MUCH AS EXPECTED AND
PERHAPS OVER PERFORMING IN SOME LOCATIONS. IN PARTICULAR, THE
MISSOULA VALLEY HAS RECEIVED MORE EFFICIENT SNOWFALL OVERNIGHT AND
THROUGH TODAY DUE TO AROUND A 25 TO 1 SNOW TO WATER RATIO. THIS
LIGHT, POWDERY SNOW HAS STACKED UP IN A HURRY AND THUS CAUSED
PERIODIC TRAVEL ISSUES THROUGHOUT THE MISSOULA AND NORTHERN
BITTERROOT VALLEYS. SINCE STEADY SNOWFALL IS EXPECTED TO RESUME
AGAIN SHORTLY AND WILL LIKELY BECOME MODERATE AT TIMES THIS
EVENING WE DECIDED TO UPGRADE THE EXISTING ADVISORY/WATCH
COMBINATION STRAIGHT TO A WINTER STORM WARNING IN EFFECT UNTIL
TUESDAY MORNING. WHILE IMPACTS TODAY WILL EBB A BIT WITH THE
PASSING WARM FRONTAL BOUNDARY, HEAVIER SNOW TONIGHT AND ESPECIALLY
ON MONDAY IN ASSOCIATION WITH AN APPROACHING ARCTIC COLD FRONT.
SIMILAR LOGIC (OVER PERFORMANCE THUS FAR COMBINED WITH ANTICIPATED
MODERATE SNOW TONIGHT) WAS USED TO UPGRADE THE BUTTE/BLACKFOOT
REGION STRAIGHT TO A WARNING.
ALL THE OTHER PREVIOUSLY ISSUED WINTER STORM WARNINGS LOOK TO BE IN
GOOD SHAPE WITH POWDERY SNOW STILL EXPECTED TO BE MEASURED IN FEET
ACROSS THE CLEARWATER/BITTERROOT AND MISSION/SWAN MOUNTAINS.
NO SIGNIFICANT CHANGES WERE MADE TO THE FORECAST IN THESE AREAS AS
ALL MODELS CONTINUE TO HAMMER THE REGION WITH AN EXTREMELY FAVORABLE
COMBINATION OF MOISTURE AND LIFT THROUGH A PERSISTENTLY DEEP SNOW
GROWTH REGION. FURTHERMORE, THE WINTER WEATHER ADVISORY FOR THE
KOOTENAI/CABINET REGION APPEARS TO BE APPROPRIATE WITH NO
SIGNIFICANT CHANGES TO THE FORECAST EXPECTED.
NEW TO THE AFTERNOON FORECAST UPDATE ARE AS FOLLOWS:
WE HAVE DECIDED TO ISSUE A WINTER WEATHER ADVISORY FOR LEMHI COUNTY
IN ANTICIPATION OF IMPACTS RELATED TO LIGHT TO MODERATE SNOWFALL.
ACCUMULATION DIFFERENCES WILL BE DRAMATICALLY DIFFERENT FROM NORTH
TO SOUTH WITH LOST TRAIL AND GIBBONSVILLE RECEIVING UPWARDS OF A
FOOT OF SNOW WHILE LEADORE PICKS UP ONLY A FEW INCHES. SALMON IN THE
MIDDLE HAS ABOUT A 90 PERCENT PROBABILITY OF 4 INCHES OF SNOW BUT A
30 PERCENT PROBABILITY OF RECEIVING UP TO 6 INCHES OF SNOW BY
TUESDAY MORNING. WE FELT THAT THE IMPACTS TYPICALLY ASSOCIATED WITH
THIS AMOUNT AND RATE OF SNOWFALL JUSTIFY AN ADVISORY.
A WINTER STORM WARNING WILL REPLACE THE ADVISORY/WATCH COMBINATION
IN THE FLATHEAD/MISSION VALLEY AS WELL AS THE WEST GLACIER REGION.
OVERALL, THE FORECAST LOGIC HAS NOT CHANGED AND GENERALLY AROUND A
FOOT OF NEW SNOW IS EXPECTED TO FALL BETWEEN NOW AND TUESDAY
MORNING. MODELS SUGGEST THE FIRST PUSH OF ARCTIC AIR MAY REACH THE
VALLEY AS EARLY AS THIS EVENING WITH A SLOW SEEPAGE OF ARCTIC AIR
CONTINUING THROUGHOUT THE DAY MONDAY. MODELS BRING THE MAIN PUSH OF
ARCTIC AIR ACROSS THE CONTINENTAL DIVIDE AND INTO THE FLATHEAD
VALLEY LATE MONDAY AFTERNOON/EARLY EVENING, JUST IN TIME FOR THE
EVENING COMMUTE. EXPECT A MARKED INCREASE IN SNOWFALL INTENSITY
JUST AHEAD AND ALONG THE FRONT ALONG WITH A PERIOD OF BLOWING AND
DRIFTING SNOW.
FINALLY, A WINTER STORM WARNING WILL REPLACE THE ADVISORY PREVIOUSLY
ISSUED FOR THE CAMAS PRAIRIE IN IDAHO. COLD AIR HAS STUBBORNLY
REMAINED IN PLACE WITH READINGS TODAY RUNNING 3 TO 5 DEGREES COOLER
THAN THE MODEL CONSENSUS. HOWEVER, IT DOES SEEM THAT SOUTHERLY WINDS
UPSTREAM WILL GRADUALLY ERODE AND MODERATE THE COLD AIR THIS
EVENING, BRIEFLY RAISING THE SNOW LEVEL. BUT THESE WINDS ARE
FORECAST TO SUBSIDE OVERNIGHT AND COOLER TEMPERATURES ALONG WITH A
LOWERING OF THE SNOW LEVEL IS EXPECTED AND SNOW WILL RETURN BY
MORNING. THE SURFACE FLOW OVER THIS AREA GRADUALLY SHIFTS TO
NORTHWESTERLY THROUGHOUT THE DAY WHICH IS CLIMATOLOGICALLY FAVORED
FOR UPSLOPE TERRAIN ENHANCED PRECIPITATION. THUS WE EXPECT THE
HEAVIEST SNOW IN PLACES LIKE GRANGEVILLE TO OCCUR MONDAY AFTERNOON
AND CONTINUE INTO TUESDAY MORNING. SOME MODELS KEEP PERSISTENT LIGHT
SNOW GOING UNTIL TUESDAY NIGHT!
ONCE AGAIN LITTLE ATTENTION WAS PLACED ON THE FORECAST BEYOND
TUESDAY. THERE REMAINS A CHANCE FOR VERY COLD TEMPERATURES WEDNESDAY
MORNING. BUT THIS WILL BE HIGHLY DEPENDENT UPON CLOUD COVER. THE
MODELS ARE STARTING TO COALESCE AROUND OUR NEXT CHANCE FOR SNOW
COMING LATE WEDNESDAY INTO THURSDAY. A FLAT RIDGE OF HIGH PRESSURE
STILL LOOKS LIKELY FOR THE WEEKEND. THOUGH HOW TEMPERATURES WARM AND
THE PRESENCE OF INVERSIONS WILL BE SOMETHING TO LOOK AT IN THE DAYS
TO COME.
AVIATION
A PROLONGED WINTER STORM REMAINS ON TRACK TO PERSIST THROUGH
TUESDAY. MODEL CROSS- SECTIONS AND FORECAST SOUNDINGS INDICATE AN
EXTENDED PERIOD OF MODERATE SNOW DEVELOPING TONIGHT, WITH
FREQUENTLY TO 1/2SM. WIDESPREAD LOW CEILINGS AND REDUCED
VISIBILITY ARE EXPECTED TO CONTINUE THROUGH MONDAY NIGHT.
EASTERLY ARCTIC WINDS HAVE FORMED JUST WEST OF THE DIVIDE, WITH
THE FRONT ANTICIPATED TO ADVANCE ACROSS WESTERN MONTANA FROM
MIDDAY MONDAY THROUGH MONDAY NIGHT. THIS WILL BRING STRONGER WINDS
AND INCREASED SNOWFALL AS THE SYSTEM MOVES IN.
MSO WATCHES/WARNINGS/ADVISORIES
MT...WINTER STORM WARNING UNTIL 9 AM MST TUESDAY FOR
BITTERROOT/SAPPHIRE MOUNTAINS...BUTTE/BLACKFOOT REGION...
LOWER CLARK FORK REGION...MISSOULA/BITTERROOT VALLEYS...
POTOMAC/SEELEY LAKE REGION.
WINTER WEATHER ADVISORY UNTIL 11 AM MST MONDAY FOR
FLATHEAD/MISSION VALLEYS...WEST GLACIER REGION.
WINTER STORM WARNING FROM 11 AM MONDAY TO 9 AM MST TUESDAY FOR
FLATHEAD/MISSION VALLEYS...WEST GLACIER REGION.
WINTER WEATHER ADVISORY UNTIL 11 PM MST MONDAY FOR
KOOTENAI/CABINET REGION.
ID...WINTER STORM WARNING UNTIL 8 AM PST TUESDAY FOR NORTHERN
CLEARWATER MOUNTAINS...SOUTHERN CLEARWATER MOUNTAINS.
WINTER WEATHER ADVISORY UNTIL 10 AM PST MONDAY FOR LOWER HELLS
CANYON/SALMON RIVER REGION...OROFINO/GRANGEVILLE REGION.
WINTER STORM WARNING FROM 10 AM MONDAY TO 8 AM PST TUESDAY FOR
OROFINO/GRANGEVILLE REGION.
WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 9 AM MST
TUESDAY FOR EASTERN LEMHI COUNTY...WESTERN LEMHI COUNTY.
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