077
FXUS65 KMSO 091023
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
423 AM MDT WED SEP 9 2026
DISCUSSION
KEY MESSAGES:
- TODAY AND THURSDAY WILL BE THE WARMEST DAYS BEFORE THE CHANGE
BACK TO FALL-LIKE WEATHER.
- CHOPPY LAKE CONDITIONS THURSDAY DUE TO WESTERLY WINDS BETWEEN
15 AND 25 MPH, AND LOCALLY HIGHER SPEEDS EXPECTED OVER THE
DIVIDE.
- STIFF NORTHEAST WINDS ARE POSSIBLE FRIDAY NIGHT THROUGH
SATURDAY...CHOPPY LAKES EXPECTED.
- CUTOFF LOW BRINGS WIDESPREAD RAIN, WITH SNOW ABOVE 7000 FEET
SATURDAY NIGHT INTO SUNDAY.
THE SATELLITE IMAGERY THIS MORNING REVEALS FOG THAT HAS DEVELOPED
IN SEVERAL VALLEYS FROM THE US-12 CORRIDOR WEST OF LOLO PASS, TO
NORTHWEST MONTANA. EXPECT ANY FOG TO BURN OFF BY MID-MORNING
TODAY. IT'S GOING TO FEEL LIKE SUMMER AGAIN AS HIGHS WILL RISE
INTO THE 70S MOST OF OUR FORECAST AREA WITH THE EXCEPTION OF THE
LOWER VALLEYS OF CENTRAL IDAHO WHERE 80S ARE EXPECTED.
A WEAKENING MOISTURE PLUME WILL SHIFT SOUTH OUT OF CANADA LATER
TONIGHT AND WILL BE OVER NORTHWEST MONTANA BY THURSDAY MORNING.
THE FORCING IS RELATIVE WEAK, BUT COULDN'T RULE OUT A FEW LIGHT
SHOWERS IN THE MOUNTAINS FROM YAAK TO GLACIER NATIONAL PARK AROUND
DAYBREAK. OTHER THAN THE INCREASE IN CLOUDS, THURSDAY WILL
GENERALLY BE A WARM, DRY AND BREEZY DAY ACROSS THE REGION.
WESTERLY WINDS WILL PICK UP IN THE AFTERNOON, GENERALLY 10 TO 15
MPH WITH GUSTS TO 25 MPH, HIGHER GUSTS OVER THE DIVIDE.
BY THURSDAY NIGHT, A WEAK FRONT WILL BECOME THE IMPETUS FOR
SHOWERS THAT CONTINUE THROUGHOUT THE DAY FRIDAY. A NORTHEAST WIND
GRADIENT DEVELOPS BY FRIDAY EVENING WHICH WILL ENHANCE SHOWER
ACTIVITY OVER THE GLACIER REGION, AND ALSO COULD CAUSE LAKE
MACDONALD TO BECOME CHOPPY.
AN IMPRESSIVE 15 MILLIBAR EASTERLY WIND/PRESSURE GRADIENT SETS UP
ON SATURDAY IN RESPONSE TO THE INCOMING LOW PRESSURE SYSTEM MOVING
ONSHORE OVER OREGON. THERE IS A 50% CHANCE THAT SUSTAINED WINDS
COULD EXCEED 15 MPH AND GUSTS EXCEED 25 MPH OVER FLATHEAD LAKE.
OTHER AREAS, ESPECIALLY CHANNELED LOCATIONS COULD ALSO EXPERIENCE
ELEVATED WINDS.
A CUT-OFF LOW PRESSURE SYSTEM WILL TRACK FROM SOUTHWEST IDAHO
SATURDAY NIGHT TO EAST OF GREAT FALLS BY SUNDAY EVENING. AS THIS
SYSTEM DOES THIS, IT WILL BRING WIDESPREAD LIGHT TO MODERATE
PRECIPITATION TO CENTRAL IDAHO AND WESTERN MONTANA. RIGHT NOW, THE
HEAVIEST PRECIPITATION BEING FORECAST BY THE NBM EXTENDS ROUGHLY
100 MILES NORTH AND SOUTH FROM A LINE FROM GRANGEVILLE, IDAHO TO
MISSOULA TO GREAT FALLS WITH A RANGE FROM 0.60" TO 1.60" OF TOTAL
PRECIPITATION. THE MOUNTAINS WITHIN THIS LINE COULD RECEIVE 1 TO 2
INCHES. THIS UPPER TROUGH IS A BIT COLDER THAN THE RECENT SYSTEM,
SO SNOW LEVELS COULD FALL TO AROUND 7000 FEET BY DAYBREAK SUNDAY
MORNING. IT COULD FEEL VERY WINTRY IN THE BACKCOUNTRY WHICH COULD
BE DANGEROUS FOR THE UNPREPARED.
A MODERATING AND DRYING TREND IS EXPECTED BY EARLY NEXT WEEK.
AVIATION
FOG HAS FILLED A FEW VALLEYS ACROSS CENTRAL IDAHO AND
NORTHWEST MONTANA THIS MORNING. EXPECT IT TO DISSIPATE BY MID-
MORNING. GPI HAD DENSE FOG EARLIER THIS MORNING, BUT INCOMING
CLOUDS ALOFT HAVE HELPED TO PREVENT IT FROM RE-DEVELOPING. EXPECT
GENERALLY WEAK WINDS AND VFR CONDITIONS TODAY. PATCHY FOG IS
POSSIBLE TONIGHT. INCOMING CLOUDS WITH A FEW LIGHT SHOWERS ARE
POSSIBLE ACROSS NORTHWEST MONTANA AROUND DAYBREAK THURSDAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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