147
FXUS65 KMSO 111025
AFDMSO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MISSOULA MT
425 AM MDT THU SEP 11 2025
DISCUSSION
KEY MESSAGES:
- THUNDERSTORMS EXPECTED THROUGH FRIDAY FEATURING GUSTY OUTFLOW
WINDS AND HEAVY RAIN, FOCUSED IN THE AFTERNOON/EVENING HOURS
- TEMPERATURES BACK TO SEASONABLE LEVELS FRIDAY THROUGH THE
WEEKEND.
- ANOTHER WEATHER SYSTEM TO BRING COOLER TEMPERATURES AND SHOWERS
LATER SUNDAY INTO MONDAY.
RESIDUAL SHOWERS ARE POSSIBLE ACROSS PORTIONS OF NORTHWEST MONTANA
THIS MORNING. SHOWERS AND THUNDERSTORMS WILL AGAIN DEVELOP THIS
AFTERNOON AND EVENING ACROSS THE REGION. THE MAIN THREATS WILL BE
GUSTY WINDS TO 45 MPH, LOCALIZED HEAVY RAIN, AND LIGHTNING. DURING
YESTERDAY'S EVENT, THERE WERE A FEW LOCATIONS THAT RECEIVED UP TO
0.50" TO 0.75" ACCORDING TO RADAR ESTIMATES. SO A LOW PROBABILITY
DEBRIS FLOW THREAT FOR SUSCEPTIBLE BURN SCARS CONTINUES. LOOKING
JUST AT FLOOD PRONE AREAS, THE LATEST HREF ENSEMBLE DEPICTS A 20%
CHANCE FOR RAINFALL RATES GREATER THAN 0.30" AT THE DALY BURN
SCAR. AT THE SAME TIME THERE ARE PLENTY OF LOCATIONS WHERE THE
PROBABILITIES ARE AT ZERO PERCENT ACROSS THE REGION. ANOTHER
IMPACT WILL BE THE CHANCE FOR SMALL HAIL IN THE THUNDERSTORMS. THE
LATEST HRRR SHOWS A FEW STORMS OVER NORTH-CENTRAL IDAHO, SOUTHERN
BITTERROOT VALLEY, AND OVER GRANITE COUNTY, THAT COULD PRODUCE
BETWEEN HALF- INCH TO 0.75" HAIL (UP TO PENNY SIZE). THE GFS
FORECAST INSTABILITY LEVELS(CLOSE TO 500 J/KG) IN THE HAIL GROWTH
ZONE WOULD CORROBORATE THIS OVER IDAHO.
ON FRIDAY, MORE SCATTERED SHOWERS AND THUNDERSTORMS BRING GUSTY
WINDS, LIGHTNING AND LOCALIZED HEAVY RAIN. THE MODELS DEPICT THAT
MORE OF THE HEAVIER SHOWERS MAY BE IN THE MOUNTAINS OF GLACIER
NATIONAL PARK, AND ALSO IN THE SALISH MOUNTAINS, LOCATED WEST OF
US-93 IN NORTHWEST MONTANA. THERE IS A 15% CHANCE THAT HEAVY RAIN
COULD IMPACT THE GOING-TO- THE-SUN ROAD.
BY FRIDAY NIGHT(AND SATURDAY NIGHT), PARTIAL CLEARING COULD ALLOW
FOR FOG DEVELOPMENT TO OCCUR. AREAS THAT SAW APPRECIABLE RAINFALL
THIS WEEK WILL HAVE THE HIGHER CHANCE FOR THAT TO OCCUR.
THE UPPER LEVEL LOW THAT HAS BEEN VERY SLOW TO TRAVERSE THE AREA
WILL FINALLY END UP OVER EASTERN MONTANA BY SATURDAY NIGHT. OUR
REGION WILL BE UNDER SLIGHTLY UNSTABLE AND CYCLONIC FLOW, WHICH
WILL BE CONDUCIVE FOR SCATTERED SHOWERS AND A FEW ISOLATED
THUNDERSTORMS ON SATURDAY, MAINLY ACROSS WESTERN MONTANA.
THERE MAY BE A BRIEF BREAK WITH SOME SUN EARLY SUNDAY BEFORE
CLOUDS INCREASE AS THE NEXT TROUGH APPROACHES FROM THE WEST.
CONFIDENCE IS HIGH FOR ANOTHER WEATHER SYSTEM TO BRING SHOWERS AND
COOLER TEMPERATURES INTO MONDAY. BUT HOW IT WILL EVOLVE IS STILL
IN QUESTION. THERE IS A CHANCE THAT THIS SYSTEM COULD CUT OFF
BRIEFLY FROM THE POLAR JET ON MONDAY, DIG SOUTH A BIT AND SLOW
DOWN. IF IT DOES THIS, THERE COULD BE ENHANCED RAINFALL ALONG ITS
NORTHERN PERIPHERY. BUT IF NOT, IT JUST TRACKS ACROSS THE REGION
AND MAKE A B-LINE TOWARDS THE NORTHERN PLAINS, THEREBY BRINGING
LESS RAINFALL AND MORE DOWNSLOPING. LOOKING AT THE ENSEMBLE
CLUSTERS WHICH TRY TO PUT "SIMILAR" SOLUTIONS IN THE SAME BIN, 62%
OF THE MODELS DEPICT MORE OF A CUT-OFF SOLUTION(WETTER/COLDER),
WHILE THE REMAINING 38% DEPICT A MORE PROGRESSIVE TROUGH PASSAGE
(DRIER/BREEZIER). IF THE WETTER AND COLDER SOLUTION WERE TO COME
INTO FRUITION, THEN SOME VALLEY LOCATIONS COULD SEE HIGHS
STRUGGLING TO GET OUT OF THE 50S OR 60S DUE TO CLOUDS AND SHOWER
ACTIVITY!
AVIATION
SCATTERED SHOWERS ACROSS NORTHWEST MONTANA THROUGH
1500Z THIS MORNING COULD BRING SOME MOUNTAIN OBSCURATION AND LOWER
VISIBILITY. ANOTHER ROUND OF THUNDERSTORMS IS EXPECTED FROM 1800Z
TO 12/0600Z TONIGHT. THREATS INCLUDE WIND GUSTS TO 45 KNOTS, SMALL
HAIL, HEAVY RAIN, MOUNTAIN OBSCURATION AND LOWER VISIBILITY AT
TIMES. SCATTERED SHOWERS AND STORMS ARE POSSIBLE ON FRIDAY, BUT
MAY NOT BE AS WIDESPREAD AS THURSDAY.
MSO WATCHES/WARNINGS/ADVISORIES
MT...NONE.
ID...NONE.
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