879
FXUS65 KTFX 132343
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
543 PM MDT MON OCT 13 2025
AVIATION SECTION UPDATED.
KEY MESSAGES
- REDUCED VISIBILITIES DUE TO FOG ARE POSSIBLE TONIGHT AND
TUESDAY MORNING ACROSS PORTIONS OF SOUTHWEST, CENTRAL, AND
NORTH CENTRAL MONTANA.
- ANOTHER ROUND OF MAINLY MOUNTAIN SNOW WILL RETURN TO SOUTHWEST
AND PORTIONS OF CENTRAL MONTANA FROM TUESDAY THROUGH THURSDAY.
- TEMPERATURES SLOWLY WARM TO NEAR AVERAGE BY THE END OF THE WEEK.
- PERIODS OF BREEZY TO WINDY CONDITIONS ARE EXPECTED HEADING INTO
THE WEEKEND.
DISCUSSION
/ISSUED 154 PM MDT MON OCT 13 2025/
- METEOROLOGICAL OVERVIEW:
A CLOSED LOW DIVING SOUTHWARD ALONG THE PACIFIC NORTHWEST COAST
WILL CONTINUE TO SUPPORT DIFLUENT FLOW OVER THE NORTHERN ROCKIES
FOR THE FIRST HALF THE WEEK. MOISTURE AND WEAK SHORTWAVES MOVING
IN FROM THE SOUTHWEST WILL BRING PERIODS OF RAIN SHOWERS AND
HIGHER MOUNTAIN SNOW TONIGHT INTO TUESDAY, MOSTLY FOR SOUTHWEST
MT. THE COLD AIR OVER CENTRAL AND NORTH-CENTRAL MT WILL SLOWLY
RETREAT NORTHWARD HEADING INTO MID- WEEK.
THE PACIFIC NORTHWEST CLOSED MID- LEVEL LOW IS EXPECTED TO PEAK
IN INTENSITY OVER CENTRAL CA BEFORE WEAKENING AND SWINGING
NORTHEASTWARD THROUGH THE GREAT BASIN AND EVENTUALLY REACHING
EASTERN MT BY AROUND THURSDAY. THE EVOLUTION OF THIS FEATURE WILL
BE COMPLEX AS IT APPROACHES THE REGION, SO THE PRECISE LOCATIONS
OF ITS LOW PRESSURE CENTER(S) AND RESULTANT PRECIPITATION
LOCATIONS IS STILL A BIT ON THE FUZZY SIDE. OVERALL EXPECT THE
MOST WIDESPREAD RAIN AND MOUNTAIN SNOW TO OCCUR BETWEEN TUESDAY
NIGHT AND FRIDAY. WITH MILDER PACIFIC AIR MOVING IN, SNOW IMPACTS
LOOK TO BE ON THE MINOR SIDE AND MOSTLY CONFINED TO MOUNTAIN
AREAS.
RIDGING ALOFT WITH STRONGER WESTERLY FLOW LOOKS TO AT LEAST
BRIEFLY MOVE THROUGH THE NORTHERN ROCKIES HEADING TOWARDS THE
WEEKEND FOLLOWED BY MORE PASSING TROUGHS IN AN INCREASINGLY
NORTHWESTERLY FLOW ALOFT. THIS WILL RESULT IN PERIODS OF BREEZY TO
WINDY CONDITIONS, THOUGH THE TIMING DETAILS STILL NEED TO BE
WORKED OUT DEPENDING TROUGH AND RIDGE PHASING. - RCG
- FORECAST CONFIDENCE & SCENARIOS:
FOG TONIGHT AND TUESDAY MORNING...
BOTH NBM AND HREF GUIDANCE SUPPORT THE POTENTIAL FOR REDUCED
VISIBILITIES DUE TO FOG DEVELOPMENT FROM THE LATE EVENING HOURS
TONIGHT THROUGH THE MORNING HOURS ON TUESDAY. THIS WILL BE
ESPECIALLY TRUE WHERE WINDS BECOME LIGHT AND VARIABLE AND/OR UPSLOPE
IN NATURE, ALONG WITH WHERE SKIES PARTLY CLEAR. WHILE SURFACE WINDS
ARE EXPECTED TO DECREASE THROUGH THE OVERNIGHT HOURS TONIGHT THE
BIGGEST SOURCE OF UNCERTAINTY WITH RESPECT TO FOG DEVELOPING IS
WITH RESPECT TO CLOUD COVER, WITH LATEST HREF GUIDANCE SUPPORTING A
50-75% CHANCE FOR THE TOTAL CLOUD COVER TO FALL BELOW 37.5% (MOSTLY
CLEAR SKIES). THE ONE EXCEPTION TO THIS WILL BE ALONG AND WEST OF
THE I-15 CORRIDOR WHERE LOW LEVEL NORTHEAST TO EASTERLY FLOW WILL
HELP TO MAINTAIN CHANCES FOR LIGHT SNOW AND/OR LOW STRATUS FOR MUCH
OF THE OVERNIGHT HOURS.
MOUNTAIN SNOW FROM WEDNESDAY THROUGH THURSDAY ...
NBM PROBABILITIES FOR SNOWFALL ACCUMULATIONS OF 2" OR MORE RANGE
FROM A 25-35% CHANCE FOR MOUNTAIN PASSES LIKE KINGS HILL, RAYNOLDS,
AND TARGHEE THROUGHOUT THE TIMEFRAME; WITH THE HIGHEST PROBABILITIES
(I.E. 60+% CHANCE) BEING AT OR ABOVE 7500FT IN ELEVATION FOR ALL OF
THE MOUNTAINS IN SOUTHWEST AND CENTRAL MONTANA. NBM PROBABILITIES
FOR 8" OR MORE OF SNOW WITHIN THE MADISON/GALLATIN RANGES AND
TOBACCO ROOT AND GRAVELLY MOUNTAINS RANGE FROM A 25-50% CHANCE FOR
ELEVATIONS AT OR ABOVE 8000FT, WHICH WOULD BE IMPACTFUL FOR THOSE
OUTDOOR RECREATIONISTS. ECMWF EFIS, PARTICULARLY FROM WEDNESDAY NIGHT
THROUGH THURSDAY AFTERNOON, ACROSS SOUTHWEST MONTANA RANGE FROM 0.5
TO 0.6 AND INDICATE AN INCREASING POTENTIAL FOR A CLIMATOLOGICALLY
UNUSUAL SNOWFALL EVENT HERE. THIS TIMEFRAME BEARS WATCHING GIVEN
CONTINUED OUTDOOR RECREATION (I.E. HUNTING SEASON), ESPECIALLY FOR
THE MOUNTAINS SOUTH OF THE I-90 CORRIDOR AND EAST OF THE I-15
CORRIDOR IN SOUTHWEST MONTANA. - MOLDAN
AVIATION
13/18Z TAF PERIOD
IFR TO LIFR CONDITIONS WILL CONTINUE TO AFFECT AIRPORTS ACROSS
NORTH CENTRAL AND SOUTHWESTERN MONTANA EVEN AS SNOW WINDS DOWN
THIS EVENING. EXPECT LOW CLOUDS TO LINGER THROUGH THE OVERNIGHT,
WITH SOME FOG POSSIBLE, ESPECIALLY AT KBZN, KEKS, KGTF, AND KCTB.
LOW CLOUDS WILL ALSO BE A CONCERN OVERNIGHT TONIGHT BEFORE A
GRADUAL RETURN TO VFR CONDITIONS ARRIVES TOMORROW AS DRIER AIR
MOVES INTO THE AREA. LUDWIG
PRELIMINARY POINT TEMPS/POPS
GTF 24 40 28 40 / 20 20 30 40
CTB 23 40 21 46 / 30 20 20 20
HLN 25 41 29 41 / 20 30 30 60
BZN 24 48 30 44 / 20 30 60 70
WYS 23 50 27 42 / 50 60 80 90
DLN 25 48 33 45 / 30 50 60 60
HVR 21 48 29 47 / 10 10 20 50
LWT 23 46 29 40 / 20 20 60 60
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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