393
FXUS65 KMSO 301925
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
125 PM MDT TUE SEP 30 2025
DISCUSSION
KEY MESSAGES:
- BREEZY CONDITIONS TOMORROW.
- COOLER, SHOWERY PATTERN CONTINUES THROUGH THE WEEK.
- A CUTOFF LOW THIS WEEKEND BRINGS MOUNTAIN SNOW POTENTIAL.
A JET OVERHEAD AND SOUTHWEST WINDS WELL ALIGNED FROM THE SURFACE
TO 30,000 FT WILL CAUSE BREEZY CONDITIONS TOMORROW. WIND GUSTS
OVER 20 MPH WILL BE COMMON AT HIGHER ELEVATIONS, THOUGH GUSTS IN
SOME SHELTERED VALLEYS MAY ONLY REACH THE TEENS. GUSTS WILL BE
STRONGER IN LEMHI AND SOUTHERN IDAHO COUNTIES IN IDAHO WHERE GUSTS
25-30 MPH WILL BE COMMON. THE CAMAS PRAIRIE AROUND GRANGEVILLE,
IDAHO AND SOUTHERN LEMHI COUNTY AROUND GILMORE SUMMIT, WILL
LIKELY SEE FREQUENT GUSTS OVER 30 MPH.
A BROAD TROUGH ACROSS THE U.S. WEST COAST WILL KEEP SOUTHWEST FLOW
AND A COOLER AIR MASS OVER THE REGION. A CLOSED LOW IN THE MIDDLE
OF THE TROUGH WILL EJECT SHORTWAVES MOVING THROUGH THE SOUTHWEST
FLOW EVERY DAY OR SO, AND THOSE SHORTWAVES WILL BE THE MAIN
DRIVERS OF SHOWERS. SO WE DO EXPECT INTERMITTENT SHOWERS AND TO
CONTINUE THROUGH THE REST OF THE WEEK.
THIS WEEKEND THAT BROAD TROUGH OFF THE WEST COAST CLOSES OFF AS A
CUTOFF LOW AND MOVES INTO THE WESTERN U.S. CUTOFF LOWS LIKE THIS
ARE TYPICALLY A CHALLENGE FOR MODELS TO FORECAST THEIR TRACK, AND
THIS ONE IS NO DIFFERENT. THERE IS QUITE A LOT OF UNCERTAINTY
ABOUT HOW FAR NORTH OR SOUTH THE LOW WILL TRACK, BUT THAT WILL
HAVE A BIG IMPACT ON THE WEATHER ACROSS THE NORTHERN ROCKIES.
A MORE SOUTHERLY TRACK FOR THE LOW, WHICH THE ENSEMBLES ARE
LEANING TOWARDS, MEANS THIS AREA WOULD BE UNDER A SPLIT FLOW
PATTERN. IN THAT PATTERN THE PRECIPITATION IS PRETTY LIGHT BUT THE
WINDS ARE STRONGER, AND SNOW ACCUMULATIONS WOULD BE LIGHT AND
LOCATED AT HIGHER ELEVATIONS. BECAUSE OF LESS CLOUD COVER, THIS
TRACK WOULD ALSO PROMOTE COLDER TEMPERATURES ON MONDAY MORNING.
THERE IS ALREADY A HIGH CHANCE (70-90 PERCENT) OF TEMPERATURES
AROUND OR BELOW 28F IN THE TYPICAL COLD SPOTS LIKE STEVENSVILLE,
HIGHWAY 98 NORTH OF WHITEFISH, OVANDO, GEORGETOWN LAKE, AND BUTTE
IN MONTANA AND ELK CITY AND RED RIVER IN CENTRAL IDAHO. WITH THE
MORE SOUTHERLY TRACK, IT WOULD LIKELY DROP INTO THE LOW 20S IN
MANY OF THESE LOCATIONS.
IF THE LOW TAKES A MORE NORTHERLY TRACK, THEN LOCATIONS LIKE
BUTTE AND ANACONDA, COULD PICK UP A COUPLE INCHES OF SNOW NEXT
WEEK. CURRENT ENSEMBLE FORECASTS HAVE A LESS THAN 10 PERCENT
CHANCE FOR AN INCH OR MORE OF SNOW DOWN TO PASS LEVELS. IN ANY
CASE, THOSE IN THE BACK COUNTRY EARLY NEXT WEEK NEED TO BE
PREPARED FOR COLD, BLUSTERY, RAW CONDITIONS WITH A POSSIBILITY FOR
SNOW.
AVIATION
A SHORTWAVE MOVING OVER THE REGION TODAY EMBEDDED IN A
BROADER TROUGH PATTERN, IS CAUSING CEILINGS AND OCCASIONAL
SHOWERS THIS AFTERNOON. ANOTHER SHORTWAVE TONIGHT WILL CAUSE
ANOTHER ROUND OF SHOWERS AS THE BROADER TROUGH SLOWLY EXPANDS
EASTWARD TONIGHT. SOME FOG OR MIST MAY FORM INTERMITTENTLY WHEN
THERE ARE CLOUD BREAKS OVERNIGHT, BUT THE CONTINUED SOUTHWEST
WINDS ALOFT WILL CAUSE ENOUGH MIXING TO LIMIT ANY IMPACTS TO
AVIATION OVERNIGHT. ONLY MINOR IMPACTS TO COMMERCIAL AVIATION ARE
EXPECTED.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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