052
FXUS65 KTFX 131755
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1155 AM MDT THU AUG 13 2026
AVIATION SECTION UPDATED.
KEY MESSAGES
- COOLER TEMPERATURES PERSIST ACROSS THE REGION THROUGH THE END
OF THE WEEK WITH SHOWERS AND THUNDERSTORMS AROUND AT TIMES.
- A FEW THUNDERSTORMS WILL BE CAPABLE OF PRODUCING HEAVY RAIN,
WHICH WOULD BE IMPACTFUL IF THEY WERE TO MOVE OVER A CITY OR
BURN SCAR.
- TEMPERATURES TREND CLOSER TO NORMAL BY THE END OF THE WEEKEND,
WITH CONTINUED OPPORTUNITIES FOR AFTERNOON AND EVENING SHOWERS
AND THUNDERSTORMS.
DISCUSSION
/ISSUED 331 AM MDT THU AUG 13 2026/
METEOROLOGICAL OVERVIEW:
A SOUTHWESTERLY FLOW ALOFT WILL MORE OR LESS PERSIST ACROSS THE
NORTHERN ROCKIES THROUGH THE WEEKEND INTO EARLY NEXT WEEK. THIS FLOW
IS INITIALLY MORE CYCLONIC IN NATURE, WHICH WILL FOSTER PLENTY OF
SHOWERS AND THUNDERSTORMS THROUGH FRIDAY EVENING ACROSS THE REGION.
PERSISTENT SURFACE WINDS FROM THE EAST AND NORTHEAST WILL CONTINUE
TO USHER IN COOLER TEMPERATURES. PRECIPITABLE WATER VALUES WILL TICK
A TOUCH HIGHER TODAY, RESULTING IN INCREASED PRECIPITATION
EFFICIENCY WITH SHOWERS AND THUNDERSTORMS THAT DEVELOP. THE MOST
ROBUST THUNDERSTORMS THAT DEVELOP OVER THE NEXT FEW DAYS WILL BE
CAPABLE OF PRODUCING AT LEAST BRIEFLY HEAVY RAINFALL. SHOULD ONE OF
THESE STRONGER STORMS MOVE OVER URBAN AREAS OR BURN SCARS, SOME
LOCALIZED FLASH FLOODING CANNOT BE RULED OUT. LIGHTNING AND GUSTY
WINDS WILL ALSO BE A CONCERN WITH STRONGER THUNDERSTORMS.
HEADING INTO THE WEEKEND THE NATURE OF THE SOUTHWESTERLY FLOW ALOFT
BECOMES A BIT MORE ANTI-CYCLONIC. THAT SAID, MOISTURE WORKING IN
FROM THE SOUTHWEST WILL COMBINE WITH TEMPERATURES TRENDING CLOSER TO
NORMAL TO RESULT IN SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS.
GREATER UNCERTAINTY IN THE PATTERN DEVELOPS TOWARD THE MIDDLE OF
NEXT WEEK. AT THIS POINT THE MAIN TAKEAWAY WILL BE FOR SCATTERED
SHOWERS AND THUNDERSTORMS MOST DAYS WITH TEMPERATURES NEAR AVERAGE.
-AM
- FORECAST CONFIDENCE & SCENARIOS:
FLASH FLOODING CONCERNS:
HREF 10KM NEIGHBORHOOD PROBABILITIES FOR A QUARTER OF AN INCH OF
RAIN OVER AN HOUR IS AT OR GREATER THAN 50% OVER THE PIONEER
MOUNTAINS TODAY. GIVEN THE RECENT INTENSE FIRE ACTIVITY RESULTING IN
HYDROPHOBIC SOILS AND STEEP TERRAIN WITHIN THE FIRE FOOTPRINT, IT
WILL NOT TAKE MUCH PRECIPITATION OVER A SHORT PERIOD TO RESULT IN
SOME FLASH FLOODING. AS SUCH, THIS AREA WAS ADDED TO A FLASH FLOOD
WATCH VALID FOR THIS AFTERNOON AND EVENING. ANOTHER FLASH FLOOD
WATCH MAY BE NECESSARY FOR THE SAME AREA FOR TOMORROW AS WELL.
ONGOING FLASH FLOOD WATCH FOR THE HORSE GULCH BURN SCAR REMAINS IN
EFFECT UNCHANGED FROM THE PREVIOUS FORECAST UPDATE.
RISK FOR STRONG THUNDERSTORMS:
WHILE INVERTED-V SOUNDINGS WILL BE AROUND ACROSS SW MT THE NEXT TWO
DAYS, THESE INVERTED-VS ARE RATHER SHALLOW ALL THINGS CONSIDERED.
THIS WILL HELP REDUCE THE RISK FOR A STRONG TO SEVERE GUST. AT THIS
TIME THE MAIN CONCERN WILL CONTINUE TO BE LIGHTNING, ASIDE FROM
BRIEFLY HEAVY RAINFALL. -AM
AVIATION
14/18Z TAF PERIOD
SCATTERED SHOWERS WILL OCCUR ACROSS ALL TERMINALS DURING THIS TAF
PERIOD, WITH THE TERMINALS WEST OF KHVR SEEING PERIODS OF
AFTERNOON THUNDERSTORMS. THESE THUNDERSTORMS ARE CAPABLE OF
PRODUCING LIGHTNING, BRIEF HEAVY RAINFALL, AND GUSTY WINDS. THE
THUNDERSTORMS AND RAIN SHOWERS WILL LOWER CEILINGS AND CREATE
MOUNTAIN OBSCURATION THROUGHOUT THE TAF PERIOD.
FOR KGTF: SURFACE WINDS WILL CONTINUE TO BLOW FROM THE NORTHEAST
UNTIL AROUND 14/07Z, IN WHICH THE DIRECTION WILL SHIFT TO A NORTH-
NORTHWESTERLY FLOW. AFTER THIS SHIFT, THE PROBABILITY OF A CROSS-
WIND IN EXCESS OF 15 KTS, WHILE SMALL, IS NON-ZERO (GENERALLY LESS
THAN 5%). HOWEVER, PASSING AFTERNOON THUNDERSTORMS ARE CAPABLE OF
PRODUCING GUSTY ERRATIC WINDS AND LOWERING VISIBILITIES TO MVFR
CONDITIONS. LIGHT RAIN SHOWERS WILL LOWER CEILINGS AND CREATE
MOUNTAIN OBSCURATION THROUGHOUT THIS TAF PERIOD. -DZOMBA
HYDROLOGY
PRECIPITABLE WATER VALUES WILL CONTINUE BE AROUND AN INCH OR
SO ACROSS THE REGION THE NEXT COUPLE DAYS. THIS WILL ALLOW FOR THE
MOST ROBUST THUNDERSTORMS TO PRODUCE AT LEAST BRIEFLY HEAVY
RAINFALL. SHOULD THESE THUNDERSTORMS MOVE OVER SENSITIVE AREAS SUCH
AS URBAN AREAS, BURN SCARS, OR ACTIVE FIRES, EXCESSIVE RAINFALL
LEADING TO FLASH FLOODING WILL BE POSSIBLE. A FLASH FLOOD WATCH IS
IN EFFECT FOR THE HORSE GULCH BURN SCAR. THE FLASH FLOOD WATCH
WAS ALSO EXPANDED TO INCLUDE THE PIONEER MOUNTAINS, WHERE STEEP
TERRAIN AND HYDROPHOBIC SOILS WILL NEED VERY LOW TOTAL RAINFALL
AMOUNTS TO RESULT IN FLASH FLOODING. -AM/BRUSDA
PRELIMINARY POINT TEMPS/POPS
GTF 67 49 64 48 / 70 90 60 50
CTB 57 43 60 43 / 100 70 50 40
HLN 71 52 68 51 / 50 80 80 70
BZN 76 49 70 47 / 40 80 90 80
WYS 71 38 66 35 / 80 80 60 70
DLN 75 48 70 45 / 60 90 90 60
HVR 65 47 68 46 / 100 50 40 40
LWT 66 47 64 45 / 80 80 80 80
TFX WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH THROUGH THIS EVENING FOR ELKHORN AND BOULDER
MOUNTAINS.
FLASH FLOOD WATCH FROM 6 PM MDT THIS EVENING THROUGH THIS
EVENING FOR BIG BELT, BRIDGER AND CASTLE MOUNTAINS.
FLASH FLOOD WATCH THROUGH THIS EVENING FOR NORTHWEST BEAVERHEAD
COUNTY.
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