434
FXUS65 KTFX 210258
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
858 PM MDT THU AUG 20 2026
KEY MESSAGES
- IT WILL BE HOT AND DRY THROUGH FRIDAY, WITH THE WARMER
TEMPERATURES EXTENDING THROUGH SUNDAY.
- THERE IS A CHANCE FOR THUNDERSTORMS IN SOUTHWEST MT FRIDAY,
WITH CHANCES FOR SHOWERS AND THUNDERSTORMS IN SOUTHWEST AND
CENTRAL MT SATURDAY AND SUNDAY.
- A COLD FRONT WILL BRING GUSTY WINDS ACROSS THE CWA SUNDAY, AND
WILL GIVE SLIGHTLY COOLER TEMPERATURES FOR MONDAY AND TUESDAY.
UPDATE
MADE CHANGES TO PRECIPITATION PROBABILITIES AND WIND GUSTS FOR
NORTHERN BLAINE COUNTY TONIGHT DUE TO LATE THUNDERSTORMS IN CANADA
TURNING TOWARDS CWA.
DISCUSSION
/ISSUED 549 PM MDT THU AUG 20 2026/
- METEOROLOGICAL OVERVIEW:
MONTANA CONTINUES TO BE UNDER THE INFLUENCE OF AN UPPER LEVEL
RIDGE TODAY, CREATING ANOTHER DAY OF WARM TEMPERATURES AND DRY
CONDITIONS. WHILE THESE WARM TEMPERATURES WILL LAST THROUGH
SUNDAY, SHORTWAVES EMBEDDED IN THE UPPER LEVEL RIDGE AND AN
INCREASE IN MONSOONAL MOISTURE WILL BRING CHANCES FOR SHOWERS AND
THUNDERSTORMS TOMORROW THROUGH THE WEEKEND. THUNDERSTORMS WILL
MAINLY IMPACT SOUTHWEST MT TOMORROW NIGHT, WITH A TRANSITION TO
MORE STRATIFORM PRECIPITATION SATURDAY MORNING. SATURDAY EVENING
WILL SEE CHANCES FOR THUNDERSTORMS IN SOUTHWEST AND CENTRAL MT,
ALTHOUGH ISOLATED CONVECTION MAY MAKE ITS WAY UP TO THE HI-LINE.
SUNDAY AFTERNOON INTO THE EVENING, THUNDERSTORM CHANCES INCREASE
TO INCLUDE SOUTHWEST, CENTRAL AND NORTH-CENTRAL MT. THE MAIN
THREAT WITH THESE THUNDERSTORMS WILL BE GUSTY WINDS, SMALL HAIL,
FREQUENT LIGHTNING AND BRIEF, HEAVY DOWNPOURS. WHILE CONDITIONS
ARE CURRENTLY NOT FAVORABLE FOR STRONG TO SEVERE STORMS THIS
WEEKEND, WE CANNOT RULE OUT THE POSSIBILITY OF AN ISOLATED ONE
FORMING.
THE UPPER LEVEL RIDGE WILL BEGIN TO BREAK DOWN ON SUNDAY AS AN
UPPER LEVEL TROUGH MOVES OVER THE NORTHERN ROCKIES FROM THE WEST.
THIS WILL BRING BREEZY CONDITIONS ACROSS THE CWA ON SUNDAY. A COLD
FRONT MOVING THROUGH SUNDAY NIGHT WILL DECREASE TEMPERATURES TO
BELOW SEASONAL AVERAGES MONDAY AND TUESDAY. HOWEVER, ANOTHER UPPER
LEVEL RIDGE BUILDING OVER MONTANA WILL CAUSE TEMPERATURES TO RISE
AGAIN ON WEDNESDAY. THIS RISE IN TEMPERATURES WILL BE SHORT LIVED
AS AN UPPER LEVEL TROUGH MOVES WEST ONCE AGAIN, LOWERING
TEMPERATURES AND BRINGING BACK CHANCES FOR SHOWERS AND
THUNDERSTORMS. -DZOMBA
- FORECAST CONFIDENCE & SCENARIOS:
THE MAIN SOURCE OF UNCERTAINTY IN THIS FORECAST IS THE TIMING OF
THE RIDGE BREAK DOWN AND SUBSEQUENT COLD FRONT. THIS TIMING WILL
DETERMINE WHEN WE SEE THE HIGHEST NON-CONVECTIVE WINDS. CURRENTLY,
MODELS ARE SHOWING THE RIDGE BEGINNING TO BREAK DOWN SUNDAY
AFTERNOON, WHICH COINCIDE WITH THE PEAK OF THE BREEZY CONDITIONS.
IF THIS RIDGE BREAK DOWN AND COLD FRONT ARRIVE EARLIER OR LATER,
THE TIMING OF THE GUSTY WINDS WILL FOLLOW SUIT.
THUNDERSTORMS:
THERE IS A 15-20% CHANCE OF THUNDERSTORMS IN SOUTHWEST MT TOMORROW
NIGHT INTO EARLY SATURDAY MORNING. ON SATURDAY, THERE IS A 25-30%
CHANCE OF THUNDERSTORMS IN SOUTHWEST MT, AND A 15-20% CHANCE OF
THUNDERSTORMS IN CENTRAL MT. NORTH-CENTRAL MT WILL SEE LOW, BUT
NON-ZERO, CHANCES OF THUNDERSTORMS SATURDAY, GENERALLY BELOW 15%.
ON SUNDAY, THERE IS A 25-40% CHANCE OF THUNDERSTORMS IN SOUTHWEST
AND CENTRAL MT, AND A 15-20% CHANCE OF THUNDERSTORMS IN NORTH-CENTRAL
MT. OVER THE WEEKEND. THE INFLOW OF MONSOONAL MOISTURE WILL
INCREASE PRECIPITABLE WATER TO OVER AN INCH, CREATING THE RISK OF
LOCALIZED FLASH FLOODING OVER BURN SCARS WITH A STRONGER
THUNDERSTORM. THE POTENTIAL FOR FLASH FLOODING WILL DEPEND ON HOW
FAST THE THUNDERSTORM IS MOVING, AND WHAT THE RAINFALL RATES
ASSOCIATED WITH IT ARE.
PRECIPITATION:
SATURDAY THROUGH SUNDAY, THERE IS A 50-70% CHANCE OF AT LEAST A
WETTING RAIN (0.1 INCHES) IN SOUTHWEST MT. THIS CHANCE DECREASES
TO A 15-30% CHANCE IN CENTRAL MT, AND A 5-15% CHANCE IN NORTH-CENTRAL
MT. FOR A QUARTER OF AN INCH DURING THIS SAME TIME PERIOD, THERE
IS A 15-25% CHANCE IN THE VALLEYS AND A 35-50% CHANCE IN THE
MOUNTAINS OF SOUTHWEST MT. THIS CHANCE DECREASES TO LESS THAN 5%
ACROSS CENTRAL AND NORTH-CENTRAL MT.
WIND:
ON SATURDAY, THERE IS A GREATER THAN 50% CHANCE FOR WIND GUSTS
GREATER THAN 25 MPH THROUGHOUT THE CWA. FOR WIND GUSTS GREATER
THAN 30 MPH, THIS CHANCE REMAINS GREATER THAN 50% EAST OF A LINE
BETWEEN HAVRE AND LEWISTOWN, AND SOUTH OF DILLON. FOR THE REST OF
THE CWA, THIS CHANCE DECREASES TO 20-45%. FOR WIND GUSTS GREATER
THAN 40 MPH, THE ONLY CONSIDERABLE CHANCE WILL BE IN NORTHERN
BLAINE COUNTY, WITH A 50-75% CHANCE.
ON SUNDAY, THERE IS A GREATER THAN 75% CHANCE OF WIND GUSTS
GREATER THAN 25 MPH ACROSS THE ENTIRE CWA. FOR WIND GUSTS GREATER
THAN 30 MPH, THERE IS A 65-85% CHANCE IN SOUTHWEST MT, A 50-80%
CHANCE IN CENTRAL MT, AND A 45-65% CHANCE IN NORTH-CENTRAL MT,
WITH THE EXCEPTION OF NORTHERN BLAINE COUNTY AND ALONG THE ROCKY
MOUNTAIN FRONT, IN WHICH CHANCES ARE 80-100%. FOR WIND GUSTS
GREATER THAN 40 MPH, THESE CHANCES DECREASE TO 25-50% IN
SOUTHWEST MT, 15-30% IN CENTRAL MT, 15-30% ALONG THE HI-LINE EAST
OF CHESTER, 20-50% ALONG THE HI-LINE WEST OF CHESTER TO CUT BANK,
AND 50-70% ALONG THE ROCKY MOUNTAIN FRONT. THERE IS A 25-50%
CHANCE OF WIND GUSTS GREATER THAN 50 MPH ALONG THE ROCKY MOUNTAIN
FRONT. -DZOMBA
AVIATION
21/00Z TAF PERIOD
VFR CONDITIONS ARE EXPECTED ACROSS THE CWA THROUGH THE PERIOD. DO
EXPECT AREAS OF MID/HIGH LEVEL CLOUDS AND SMOKE. THE SMOKE WILL
OBSCURE DISTANT MOUNTAIN RANGES ACROSS THE CWA THROUGH THE PERIOD.
THERE IS A CHANCE FOR A FEW THUNDERSTORMS OVER FAR SOUTHWEST MT ON
FRIDAY, MOSTLY AFTER 22Z.
FOR KGTF: EXPECT LIGHT AND VARIABLE WINDS AROUND THE GREAT FALLS
AREA OVER THE NEXT 24 HOURS. OVERALL MOST WIND SPEEDS WILL BE LESS
THAN 8 KNOTS, THUS THE PROBABILITY OF CROSS WINDS OVER 15 KNOTS IS
GENERALLY LESS THAN 10 PERCENT THROUGH THE PERIOD. THE NEXT CHANCE
FOR THUNDERSTORMS LOOKS TO BE LATE SATURDAY MORNING AND THEN AGAIN
EARLY ON SATURDAY EVENING. BRUSDA
PRELIMINARY POINT TEMPS/POPS
GTF 56 87 59 90 / 0 0 0 10
CTB 52 82 54 85 / 0 0 0 10
HLN 58 91 60 89 / 0 0 10 30
BZN 54 91 56 88 / 0 0 10 30
WYS 46 89 49 81 / 0 0 10 40
DLN 54 89 57 86 / 0 0 20 40
HVR 55 89 59 93 / 0 0 0 0
LWT 55 85 57 88 / 0 0 0 10
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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