795
FXUS65 KTFX 220438
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1038 PM MDT TUE JUL 21 2026
AVIATION SECTION UPDATED.
KEY MESSAGES
- SHOWERS AND THUNDERSTORMS ARE EXPECTED EACH AFTERNOON THROUGH
SATURDAY.
- ISOLATED THUNDERSTORMS IN SOUTHWESTERN MONTANA HAVE THE
POTENTIAL TO PRODUCE LOCALIZED FLASH FLOODING WEDNESDAY
AFTERNOON/EVENING.
- TEMPERATURES WILL GRADUALLY WARM UP THROUGH SATURDAY AND STAY
WARM THROUGH EARLY NEXT WEEK.
DISCUSSION
/ISSUED 551 PM MDT TUE JUL 21 2026/
- METEOROLOGICAL OVERVIEW:
AN UPPER-LEVEL RIDGE IS OVER NORTH-CENTRAL, CENTRAL, AND
SOUTHWESTERN MONTANA THIS AFTERNOON. THIS WILL ALLOW TEMPERATURES
TO WARM UP THIS AFTERNOON. MONSOONAL MOISTURE IS BEGINNING TO WORK
ITS WAY IN OVER THE AREA THIS AFTERNOON. THIS WILL BRING A FEW
ISOLATED SHOWERS AND THUNDERSTORMS TO NORTH-CENTRAL, CENTRAL, AND
SOUTHWESTERN MONTANA THIS AFTERNOON. ON WEDNESDAY THE UPPER-LEVEL
RIDGE REMAINS OVER NORTH-CENTRAL, CENTRAL, AND SOUTHWESTERN
MONTANA. AN UPPER-LEVEL SHORTWAVE WILL MOVE THROUGH THE UPPER-
LEVEL FLOW AND BRING SHOWERS AND THUNDERSTORMS PRIMARILY SOUTH OF
I-90 WEDNESDAY AFTERNOON AND EVENING. DUE TO AN INCREASE IN
MONSOONAL MOISTURE THE THUNDERSTORMS WILL PRODUCE HEAVY RAINFALL.
THERE IS A LACK OF STEERING FLOW SO THE THUNDERSTORMS WILL ALSO BE
SLOW MOVING. THIS HAS THE POTENTIAL TO LEAD TO SOME LOCALIZED
FLOODING. SEE THE HYDROLOGY SECTION FOR DETAILS. ON WEDNESDAY
ISOLATED SHOWERS AND THUNDERSTORMS HAVE THE POTENTIAL TO MAKE IT
FURTHER NORTH BUT STAY SOUTH OF AN AUGUSTA TO GREAT FALLS TO
LEWISTOWN LINE.
ON THURSDAY THE UPPER-LEVEL RIDGE REMAINS OVER NORTH-CENTRAL,
CENTRAL, AND SOUTHWESTERN MONTANA. ANOTHER UPPER-LEVEL SHORTWAVE
MOVE THROUGH THE FLOW. THIS WILL BRING ANOTHER DAY OF HOT WEATHER
WITH ISOLATED SHOWERS AND THUNDERSTORMS. ON FRIDAY THE UPPER-LEVEL
RIDGE REMAINS OVER NORTH-CENTRAL, CENTRAL, AND SOUTHWESTERN MONTANA.
THIS WILL INCREASE TEMPERATURES TO WELL-ABOVE SEASONAL AVERAGES.
WINDS WILL INCREASE DUE TO LOW-LEVEL AND MID-LEVEL WINDS INCREASING.
THIS WILL DRY OUT THE AREA AND BRING ELEVATED FIRE WEATHER
CONDITIONS TO NORTH-CENTRAL MONTANA. ON SATURDAY THE UPPER-LEVEL
RIDGE REMAINS OVER NORTH-CENTRAL, CENTRAL, AND SOUTHWESTERN
MONTANA. IT WILL BE THE HOTTEST OUT OF THIS FORECAST PERIOD ACROSS
THE AREA ON SATURDAY WITH WELL-ABOVE SEASONAL AVERAGE TEMPERATURES.
ON SUNDAY A WEAK UPPER-LEVEL TROUGH MOVES THROUGH WHICH WILL
SLIGHTLY COOL DOWN TEMPERATURES AND BRING SOME WINDY CONDITIONS TO
THE AREA. ON MONDAY THE UPPER-LEVEL RIDGE REMAINS OVER NORTH-
CENTRAL, CENTRAL, AND SOUTHWESTERN. THIS WILL ALLOW WARM AND DRY
CONDITIONS TO PERSIST. -IG
- FORECAST CONFIDENCE & SCENARIOS:
ON WEDNESDAY THERE IS A 40 - 60% CHANCE FOR THUNDERSTORMS ACROSS
SOUTHWESTERN MONTANA. ON WEDNESDAY THERE IS A 15 - 35% CHANCE FOR
THUNDERSTORMS ACROSS MOST OF NORTH-CENTRAL AND CENTRAL MONTANA. ON
THURSDAY THERE IS A 20 - 40% CHANCE FOR THUNDERSTORMS ACROSS NORTH-
CENTRAL, CENTRAL, AND SOUTHWESTERN MONTANA. ON FRIDAY THERE IS A 25 -
30% CHANCE FOR THUNDERSTORMS ACROSS SOUTHWESTERN MONTANA. ON
SATURDAY THERE IS A 25 - 40% CHANCE FOR THUNDERSTORMS ACROSS
SOUTHWESTERN MONTANA.
ON FRIDAY THERE IS A 40 - 80% CHANCE FOR HIGH TEMPERATURES OF 100
DEGREES OR GREATER ACROSS MOST OF NORTH-CENTRAL MONTANA. ON SATURDAY
THERE IS GREATER THAN A 60% CHANCE FOR HIGH TEMPERATURES OF 100
DEGREES OR GREATER ACROSS NORTH-CENTRAL MONTANA. ON SATURDAY
THERE IS A 30 - 50% CHANCE FOR HIGH TEMPERATURES OF 100 DEGREES OR
GREATER FROM THE HELENA VALLEY THROUGH THE CANYON FERRY AREA TO
TOWNSEND TO THE THREE FORKS TO BOZEMAN AREA. -IG
AVIATION
22/06Z TAF PERIOD
MONSOON MOISTURE WILL CONTINUE TO STREAM IN FROM THE
WEST/SOUTHWEST AND BRING VARIABLY CLOUDY SKIES AND PERIODS OF
SCATTERED SHOWERS AND THUNDERSTORMS. CONVECTIVE ACTIVITY CURRENTLY
SITUATED ALONG THE MT/ID/WY BORDERS WILL SLOWLY DIMINISH AND END
DURING THE OVERNIGHT HOURS. PATCHY FOG WILL THEN DEVELOP AND MAY
BRING COMPROMISED FLIGHT CATEGORIES IN THE KWYS AREA BETWEEN 22/09
AND 22/15Z. A SUBTLE SHORTWAVE MOVES IN AND INITIATES SCATTERED
TO NUMEROUS SHOWERS AND THUNDERSTORMS OVER SOUTHWEST AND PORTIONS
OF CENTRAL MT BETWEEN 22/18 AND 23/06Z. THE PRIMARY CONCERN WITH
THIS ACTIVITY WILL BE BRIEF HEAVY DOWNPOURS, LIGHTNING, AND
GUSTY/ERRATIC WINDS. MVFR AND EVEN LOWER FLIGHT CATEGORIES WILL BE
PRESENT BENEATH SHOWERS AND STORMS. - RCG
HYDROLOGY
ON WEDNESDAY THE WEATHER PREDICTION CENTER (WPC) HAS ISSUED A
SLIGHT RISK (15% CHANCE FOR FLASH FLOODING WITHIN 25 MILES OF A
POINT) FOR FLASH FLOODING ACROSS MOST OF SOUTHWESTERN MONTANA.
BETWEEN THE I-90 CORRIDOR AND A LINE BETWEEN AUGUSTA TO GREAT
FALLS TO LEWISTOWN WPC HAS ISSUED A MARGINAL RISK (5% CHANCE FOR
FLASH FLOODING WITHIN 25 MILES OF A POINT)FOR FLASH FLOODING ON
WEDNESDAY. IN ADDITION ACROSS THE MOUNTAINS OF SOUTHWESTERN
MONTANA THERE IS A 50 - 70% CHANCE FOR RAINFALL RATES IN EXCESS OF
ONE HALF INCH PER HOUR ON WEDNESDAY. IN ADDITION THERE IS AROUND
A 50% CHANCE FOR RAINFALL RATES IN EXCESS OF THREE QUARTER OF AN
INCH PER HOUR ACROSS THE MOUNTAINS OF SOUTHWESTERN MONTANA ON
WEDNESDAY. THERE IS A 20 - 40% CHANCE FOR AN INCH OF RAIN OR
GREATER ACROSS THE MOUNTAINS OF SOUTHWESTERN MONTANA ON WEDNESDAY.
AS A RESULT A FLASH FLOOD WATCH WAS ISSUED FOR THE MOUNTAINS
SOUTH OF I-90 FROM NOON TO MIDNIGHT ON WEDNESDAY. -IG
PRELIMINARY POINT TEMPS/POPS
GTF 60 90 62 95 / 10 0 10 10
CTB 55 87 58 93 / 10 0 10 0
HLN 62 90 63 92 / 10 20 30 20
BZN 58 90 58 90 / 10 40 50 30
WYS 51 82 51 81 / 30 70 70 50
DLN 57 85 55 86 / 40 60 60 20
HVR 57 93 60 100 / 10 0 0 10
LWT 55 86 57 89 / 10 10 10 30
TFX WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY EVENING
FOR GALLATIN AND MADISON COUNTY MOUNTAINS AND CENTENNIAL
MOUNTAINS-NORTHWEST BEAVERHEAD COUNTY-RUBY MOUNTAINS AND
SOUTHERN BEAVERHEAD MOUNTAINS.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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