634
FXUS65 KTFX 110954
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
354 AM MDT SAT OCT 11 2025
KEY MESSAGES
- A SIGNIFICANT PATTERN CHANGE BEGINS TODAY, TRANSITIONING TO
BREEZY TO WINDY CONDITIONS WITH SCATTERED SHOWERS AND
THUNDERSTORMS.
- WIDESPREAD PRECIPITATION, ACCUMULATING SNOW, AND MUCH
COOLER TEMPERATURES ARE EXPECTED TONIGHT THROUGH MONDAY.
- TEMPERATURES WARM SLIGHTLY NEXT WEEK, BUT THERE WILL BE DAY TO
DAY OPPORTUNITIES FOR SCATTERED SHOWER ACTIVITY AND MOUNTAIN
SNOW.
DISCUSSION
- METEOROLOGICAL OVERVIEW:
SOUTHWESTERLY FLOW ALOFT CONTINUES TODAY WHILE A PACIFIC TROUGH
APPROACHES FROM THE WEST. THIS WILL ADVECT MOISTURE NORTHWARD INTO
THE REGION AND BRING SCATTERED SHOWER ACTIVITY AND ISOLATED
THUNDERSTORMS. PRECIPITABLE WATER VALUES APPROACHING THE 0.75 INCH
MARK COMBINED WITH CAPE VALUES IN THE 100 TO 400 J/KG LEVEL MAY
RESULT IN A FEW STORMS PRODUCING LOCALIZED HEAVY DOWNPOURS IN
ADDITION TO ISOLATED INSTANCES GUSTY WINDS, AND PERHAPS SOME HAIL,
MOSTLY FOR AREAS ALONG AND SOUTHEAST OF A DILLON TO HAVRE LINE.
SOUTH TO SOUTHWESTERLY H700 WINDS ON THE ORDER OF 25 TO 35 KTS
WILL BRING BREEZY TO WINDY CONDITIONS TODAY, MOST NOTABLY TO THE
SOUTHWEST MOUNTAIN PEAKS, THE SOUTH TO NORTH ORIENTED SOUTHWEST
VALLEYS, AND AREAS ALONG THE ALONG THE ROCKY MOUNTAIN FRONT.
THE MAIN TROUGH SWINGS INTO THE NORTHERN ROCKIES AND BRINGS
PERIODS WIDESPREAD PRECIPITATION TONIGHT THROUGH MONDAY WITH H700
TEMPERATURES FALLING TO AROUND -10C OVER CENTRAL/NORTH-CENTRAL MT
FOLLOWING A CANADIAN COLD FRONTAL PASSAGE. THESE MIDDLE AND LOW
LEVEL TEMPERATURES WILL BE SUFFICIENT TO SUPPORT HEAVY SNOW IN THE
MOUNTAINS AND AT LEAST SOME LOWER ELEVATION ACCUMULATIONS. THERE
WILL BE TWO DISTINCT PERIODS OF SNOW TO FOCUS ON, WITH THE FIRST
BEING DRIVEN BY FORCING FROM THE TROUGH/COLD FRONT TONIGHT THROUGH
SUNDAY MORNING. THERE WILL BE A GENERAL LULL IN ACTIVITY DURING
THE DAY ON SUNDAY BEFORE WARM AIR ADVECTION/ISENTROPIC LIFT AND
LOW LEVEL EASTERLY FLOW INITIATE THE SECOND ROUND SUNDAY NIGHT
INTO EARLY MONDAY. THIS SECOND ROUND WILL BE MOSTLY FOCUSED ALONG
THE ROCKY MOUNTAIN FRONT AND THE PLAINS.
THE SOUTHERN PORTION OF THE MAIN TROUGH SHEARS OFF AND QUICKLY
WEAKENS AS IT HEADS OFF TO THE EAST EARLY NEXT WEEK WHILE THE
STRONGER NORTHERN PORTION OF THE CIRCULATION STRENGTHENS AND
RETROGRADES SOUTHWEST TOWARDS THE PACIFIC COAST. MOST ENSEMBLES
FAVOR WEAK DIFLUENT FLOW ALOFT OVER THE NORTHERN ROCKIES FOR
CONTINUED BELOW AVERAGE TEMPERATURES AND DAY TO DAY LOWER GRADE
SHOWER AND MOUNTAIN SNOW ACTIVITY FOR THE FIRST HALF OF THE WEEK.
THE PACIFIC NORTHWEST TROUGH THEN MOVES INTO MONTANA LATE
WEDNESDAY THROUGH FRIDAY, THOUGH THE PRECISE DETAILS OF THE
TROUGH'S EVOLUTION IS UNCLEAR AT THIS TIME. OVERALL, THERE'S AN
EXPECTATION FOR INCREASED PRECIPITATION AND MOUNTAIN SNOW FOR THE
SECOND HALF OF THE WORKWEEK WHILE TEMPERATURES WARM SLIGHTLY.
- RCG
- FORECAST CONFIDENCE & SCENARIOS:
SHOWERS AND THUNDERSTORMS TODAY...
THERE WILL BE SUFFICIENT MOISTURE AND INSTABILITY FOR SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS TODAY, MOSTLY OVER CENTRAL AND
SOUTHWEST MT. THE SHOWERS AND STORMS WILL BE CAPABLE OF MIXING DOWN
25 TO 35 KT LOWER AND MID- LEVEL WINDS TO THE SURFACE, THOUGH
PROBABILITIES FOR CONVECTIVE WIND GUSTS OVER 35 MPH DROPS OFF TO LESS
THAN 30% THIS AFTERNOON ACCORDING TO THE LATEST HREF ENSEMBLES.
ISOLATED INSTANCES OF HEAVY DOWNPOURS MAY POSE A 5% CHANCE LOCALIZED
FLOODING RISK TO SUSCEPTIBLE BURN SCARS, NAMELY THE HORSE GULCH AND
WEST FORK BURN SCARS.
SNOW SATURDAY NIGHT THROUGH MONDAY...
SNOW LEVELS BEGIN TO FALL IN A NORTHWEST TO SOUTHEAST FASHION LATE
THIS AFTERNOON THROUGH EARLY SUNDAY. CENTRAL AND NORTHERN AREAS WILL
HAVE TWO DISTINCT PERIODS OF MORE WIDESPREAD SNOW, THE FIRST TONIGHT
INTO SUNDAY MORNING AND THEN AGAIN SUNDAY NIGHT INTO MONDAY MORNING.
THE HEAVIEST SNOW FOR NORTHERN AREAS IS STILL EXPECTED ALONG THE
ROCKY MOUNTAIN FRONT AND THE ADJACENT FOOTHILLS TO THE EAST FOLLOWED
BY THE CENTRAL ISLAND RANGES AND THEIR NORTHERLY UPSLOPE FOOTHILLS.
THESE AREAS STAND A 70 TO 90% + CHANCE FOR 6 INCHES OF SNOW OVER A
48 HOUR PERIOD ENDING 6 PM MONDAY. PLAINS LOCATIONS WEST OF I15 AND
ALONG HIGHWAY 200/87 FROM ROGERS PASS TO THE GEYSER AREA HAVE A 30
TO 40% CHANCE FOR SEEING 3 INCHES OR MORE OF SNOW FOR THE SAME
TIMEFRAME, THOUGH AT LEAST SOME OF THIS MAY BE MELTED BY WARMER
SURFACE TEMPERATURES, ESPECIALLY DURING THE FIRST PERIOD OF SNOW
TONIGHT AND SUNDAY MORNING. IMPACTS WILL BE GREATEST IN THE GLACIER
NATIONAL PARK AREA WHERE OUTDOOR RECREATION MAY BECOME DANGEROUS
WITH NEAR OR IMPASSIBLE PARK ROUTES. SNOW INDUCED INFRASTRUCTURE
FAILURES AND POWER OUTAGES CAN ALSO BE EXPECTED. CHANGES TO THE
WINTER WEATHER HIGHLIGHTS INCLUDED AN UPGRADE OF THE LITTLE BELTS
ZONE TO A WINTER WEATHER ADVISORY AND THEN ADDING THE ROCKY MOUNTAIN
FRONT HIGH PLAINS ZONES AND MACDONALD PASS AREAS TO THE ADVISORY AS
WELL. ADDITIONAL ADVISORIES WILL BE CONSIDERED BY FUTURE SHIFTS FOR
CENTRAL AND NORTH-CENTRAL AREAS SUNDAY NIGHT INTO MONDAY, INCLUDING
THE CANYON AREA BETWEEN HELENA AND GREAT FALLS.
MID-LEVEL TEMPERATURES WILL NOT BE AS COLD IN THE SOUTHWEST, THOUGH
-5 TO -10C H700 TEMPERATURES WILL STILL BE COLD ENOUGH TO LOWER SNOW
LEVELS TO THE SURFACE AT LEAST BRIEFLY. ADDITIONALLY, THE CORE OF
HEAVIEST QPF IS EXPECTED HERE WITH MOUNTAIN AREAS SOUTHEAST OF A
DILLON TO BOZEMAN LINE SEEING PROBABILITIES OF 50 TO 70% CHANCE FOR
1 INCH OF LIQUID EQUIVALENT PRECIPITATION THIS EVENING THROUGH
SUNDAY. GIVEN THE SETUP, THE MADISON AND GALLATIN RANGES ABOVE 6,000
FEET WILL SEE THE HIGHEST SNOW TOTALS WITH PROBABILITIES FOR 6
INCHES OF SNOW OR MORE RUNNING IN THE 50 TO 70% CHANCE RANGE FOR THE
SAME TIMEFRAME. IMPACTS IN THE SOUTHWEST WILL BE GREATEST FOR
OUTDOOR INTERESTS TONIGHT THROUGH SUNDAY MORNING FOR AREAS IN THE
MOUNTAINS AND FOR THOSE TRAVELING ON SNOWY/MUDDY FOREST ROADS. THE
WINTER STORM WATCH FOR THE MADISON/GALLATIN RANGES WAS UPGRADED TO A
WINTER WEATHER ADVISORY, ALTHOUGH THE TIME WAS LIMITED TO TONIGHT
AND SUNDAY MORNING. - RCG
AVIATION
11/06Z TAF PERIOD
INITIAL CONCERN THIS TAF PERIOD WILL BE FOR SHOWERS AND A FEW
ISOLATED THUNDERSTORMS LIFTING NORTHWARD ACROSS PORTIONS OF
SOUTHWEST MONTANA. A FEW INSTANCES OF LLWS CANNOT BE RULED OUT
THROUGH THE OVERNIGHT, WITH CONFIDENCE BEING TOO LOW TO WARRANT A
PERSISTENT MENTION OF IT AT ANY TAF SITE.
ANOTHER PERIOD OF SHOWERS AND THUNDERSTORMS DEVELOPS IN THE
AFTERNOON SATURDAY, MOSTLY ACROSS SOUTHWEST MONTANA. PRECIPITATION
(PRIMARILY RAIN AT LOWER ELEVATIONS, SNOW IN THE MOUNTAINS)
TRENDS MORE STRATIFORM IN NATURE SATURDAY EVENING, WITH A COLD
FRONT MOVING SOUTH ACROSS THE CANADIAN BORDER SATURDAY NIGHT. LOW
CLOUDS WILL BECOME AN INCREASINGLY WIDESPREAD IMPACT LATE DAY
SATURDAY INTO SATURDAY NIGHT. MOUNTAIN OBSCURATION WILL INCREASE
THROUGH THE DAY SATURDAY. -AM
HYDROLOGY
AS SHOWERS AND THUNDERSTORMS PUSH INTO THE AREA TODAY, A FEW OF
THE SHOWERS AND STORMS MAY PRODUCE SOME HIGHLY LOCALIZED HEAVY
RAINFALL. WHILE WIDESPREAD FLOODING IS NOT EXPECTED AT THIS TIME,
THERE IS A LOW (5% OR SO) CHANCE THAT A BURN SCAR FLASH FLOOD
COULD OCCUR AT EITHER HORSE GULCH OR WEST FORK BURN SCARS.
PRELIMINARY POINT TEMPS/POPS
GTF 69 34 38 26 / 40 80 90 90
CTB 63 29 35 21 / 20 80 80 80
HLN 65 35 43 26 / 60 80 90 90
BZN 68 33 49 26 / 90 100 60 40
WYS 54 23 39 16 / 90 90 70 10
DLN 63 32 50 28 / 70 80 20 30
HVR 73 32 41 22 / 20 60 60 30
LWT 70 30 40 24 / 80 90 70 60
TFX WATCHES/WARNINGS/ADVISORIES
WINTER STORM WARNING FROM 6 PM THIS EVENING TO NOON MDT MONDAY
FOR EAST GLACIER PARK REGION-SOUTHERN ROCKY MOUNTAIN FRONT.
WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON MDT MONDAY
FOR LITTLE BELT AND HIGHWOOD MOUNTAINS-NORTHERN HIGH PLAINS-
SOUTHERN HIGH PLAINS-UPPER BLACKFOOT AND MACDONALD PASS.
WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO NOON MDT
SUNDAY FOR GALLATIN AND MADISON COUNTY MOUNTAINS AND CENTENNIAL
MOUNTAINS.
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