180
FXUS65 KMSO 152119 CCA
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
254 PM MDT TUE SEP 15 2026
DISCUSSION
KEY MESSAGES:
- COOL AND SHOWERY CONDITIONS ARE EXPECTED FROM YAAK TO GLACIER
NATIONAL PARK THROUGH THIS EVENING.
- WARMING AND DRYING TREND EXPECTED THROUGH WEDNESDAY.
- SHOWER AND THUNDERSTORM PATTERN DEVELOPS THURSDAY AND CONTINUES
INTO SATURDAY.
- ANOTHER WARMING AND DRYING TREND SUNDAY THROUGH EARLY NEXT
WEEK.
SATELLITE IMAGERY THIS AFTERNOON SHOWS A LARGE UPPER LEVEL LOW
DIGGING SOUTHWARDS FROM VANCOUVER ISLAND TOWARDS NORTHERN
CALIFORNIA. TO THE EAST OF THIS FEATURE, A STEADY STREAM OF CLOUDS
CAN BE SEEN TRACKING OVER NORTHERN IDAHO INTO NORTHWEST MONTANA. A
SHORTWAVE TROUGH WILL SLOWLY TRACK EASTWARDS ALONG THE CANADIAN
BORDER AND CONTINUE TO PRODUCE SHOWERS THROUGH THIS EVENING. SO
IF YOU'RE PLANNING ON BEING OUTSIDE FROM YAAK TO EUREKA TO GLACIER,
YOU MAY WANT TO BRING A JACKET. DESPITE THE CLOUD COVER,
TEMPERATURES ARE GENERALLY 5 TO 10 DEGREES WARMER THAN THEY WERE
AT THIS TIME YESTERDAY. HIGHS WILL WARM INTO THE LOW 60S ACROSS
NORTHWEST MONTANA. FURTHER SOUTH THE CLOUDS ARE THINNER OR
NONEXISTENT, SO EXPECT WARMER TEMPERATURES RISING INTO THE 60S
AND 70S, ESPECIALLY OVER CENTRAL IDAHO AND LEMHI COUNTY.
ON WEDNESDAY, THE TROUGH WILL MOVE EASTWARDS TOWARDS CENTRAL MONTANA
AND INDUCE A 1026 MILLIBAR HIGH NEAR CUT BANK. THIS FEATURE COMBINED
WITH LOWER PRESSURE OVER SOUTHERN IDAHO WILL PRODUCE A NORTHEAST
WIND GRADIENT ACROSS THE REGION. WINDS OF 10 TO 20 MPH ARE EXPECTED
DURING THE DAY. BY THE EVENING TIME, THE GRADIENT WILL TIGHTEN A BIT
AND EASTERLY GUSTS EXCEEDING 25 MPH COULD BE FOUND (70-80% CHANCE)
IN THE CHANNELED AREAS ALONG AND WEST OF THE CONTINENTAL DIVIDE.
THERE IS A 82% CHANCE THAT WINDS COULD EXCEED 30 MPH BETWEEN SALMON
AND TENDOY ALONG HIGHWAY 28 DURING THE EVENING HOURS. OTHER THAN THE
WINDS, HIGHS WILL BE NEAR SEASONABLE LEVELS...70S ACROSS WESTERN
MONTANA, AND 80S IN IDAHO.
ON THURSDAY THE UPPER LOW THAT WE MENTIONED IN THE BEGINNING WILL
START TO WOBBLE NORTHEASTWARDS TOWARDS SOUTHERN IDAHO.
IT WILL DRAW UP MONSOON MOISTURE OVER 200 PERCENT OF NORMAL FROM THE
FOUR CORNERS REGION. WIND SHEAR HAS TRENDED TO BE STRONGER AS THIS
SYSTEM COULD BRING A 45 KNOT MID-LEVEL JET STREAK BY THURSDAY NIGHT.
THIS MEANS THAT NOT ONLY WILL ANY THUNDERSTORMS PRODUCE A LOT OF
RAIN, THEY COULD CONTAIN HAIL. INITIALLY GUIDANCE IS SHOWING LESS
THAN 300 J/KG CAPE/INSTABILITY IN THE HAIL GROWTH ZONE ON THURSDAY
WHICH COULD SUPPORT SMALL HAIL. ON FRIDAY, DEPENDING ON HOW MUCH
HEATING WE'RE ABLE TO GET, THE HAIL POTENTIAL SEEMS TO BE GREATER
WITH THE GFS SHOWING MUCH HIGHER INSTABILITY VALUES THAT COULD
SUPPORT HAIL TO ONE INCH OR GREATER. LIGHTNING AND GUSTY WINDS WILL
BE OTHER THREATS WITH THE STORMS. THE NBM, ENSEMBLE AND AI GUIDANCE
ARE DEPICTING THE AREA FROM CENTRAL IDAHO EAST AND NORTH INCLUDING
WEST-CENTRAL AND SOUTHWEST MONTANA AS BEING THE AREAS WITH THE
HIGHEST PROBABILITY FOR THUNDERSTORMS.
AS THE LOW PULLS AWAY FROM THE REGION ON SATURDAY, THE FOCUS FOR
SHOWERS AND THUNDERSTORMS SHIFTS EASTWARDS FROM US-93 CORRIDOR
EASTWARDS INTO CENTRAL MONTANA. WE COULD HAVE LINGERING CLOUDS OVER
CENTRAL IDAHO BUT THE LOWER VALLEYS COULD REMAIN MOSTLY DRY WITH
MODERATING TEMPERATURES.
MODEL GUIDANCE CONTINUES TO SHOW LARGE UPPER RIDGING DEVELOPING
SUNDAY INTO EARLY NEXT WEEK. WE COULD HAVE PATCHY FOG DEVELOPING
ALONG RIVER BOTTOMS EACH MORNING. IF YOU TAKE THE FULL POTENTIAL,
HIGHS COULD CRACK THE 80-DEGREE MARK IN MISSOULA, WHICH WOULD BE
AROUND 10 DEGREES ABOVE AVERAGE. THE HIGHEST PROBABILITIES FOR 80S
ARE IN THE LOWER VALLEYS OF IDAHO (80-90%). THIS RIDGE WOULD BRING
US BACK TO SUMMER-LIKE CONDITIONS FOR 2-3 DAYS. THERE ARE HINTS THAT
THERE COULD BE A FRONTAL SYSTEM THAT COULD TEMPER THINGS A BIT BY
MID- WEEK.
AVIATION
A WAVE WILL BRING A CHANCE FOR SHOWERS ACROSS FAR
NORTHWEST MONTANA THROUGH DAYBREAK WEDNESDAY. EXPECT PERIODIC
CEILING CHANGES AND MOUNTAIN OBSCURATION FROM YAAK TO GLACIER
NATIONAL PARK. THE SHOWERS ARE EXPECTED TO REMAIN MORE OVER THE
MOUNTAINS NEAR GPI, BUT COULDN'T RULE OUT OCCASIONAL SPRINKLES.
OTHER LOCATIONS WILL HAVE LESS MIDDLE CLOUD COVER. A NORTHERLY
WIND GRADIENT MAY HELP TO ENHANCE THE EARLY EVENING NORTH WINDS AT
KMSO, AND KGPI MAY EXPERIENCE MORE VARIABLE WIND RATHER THAN THE
TYPICAL SOUTHERLY LAKE BREEZE. A STRONGER NORTHEAST WIND GRADIENT
WILL DEVELOP ON WEDNESDAY, GENERALLY RANGING BETWEEN 10 TO 20
KNOTS DURING THE DAY. CHANNELED TERRAIN ALONG AND WEST OF THE
DIVIDE COULD HAVE HIGHER AMOUNTS. OTHER THAN THE WIND, VFR
CONDITIONS ARE EXPECTED.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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