062
FXUS65 KTFX 190925 AAA
AFDTFX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GREAT FALLS MT
325 AM MDT SAT SEP 19 2026
KEY MESSAGES
- LOCALIZED FLOODING POSSIBLE IN AREAS WITH MODERATE RAINFALL
ACROSS PARTS OF CENTRAL AND SOUTHWEST MONTANA TODAY.
- DRIER AND WARMER WEATHER PATTERN DEVELOPS FOR THE UPCOMING WEEK
DISCUSSION
- METEOROLOGICAL OVERVIEW:
A VERTICALLY STACKED MID-TO-UPPER LEVEL LOW, CENTERED OVER SOUTHERN
IDAHO EARLY THIS MORNING, WILL SLOWLY TRACK EAST INTO WYOMING
THROUGH TONIGHT WHILE GRADUALLY WEAKENING. THIS SETUP WILL SUSTAIN A
DEEP, ANOMALOUSLY MOIST EASTERLY FLOW ACROSS SOUTHWESTERN MONTANA
TODAY. WIDESPREAD AND LOCALLY MODERATE TO HEAVY RAIN THIS MORNING
WILL CONCENTRATE ALONG AND SOUTH OF A DEFORMATION/CONVERGENCE AXIS
EXTENDING EASTWARD ACROSS CENTRAL MONTANA NORTH OF THE LOW.
CONVERSELY, AREAS NORTH OF THIS AXIS WILL EXPERIENCE LITTLE TO NO
PRECIPITATION. BY THIS AFTERNOON, RAINFALL WILL TRANSITION TO A MORE
SHOWERY PATTERN AND PIVOT BACK SOUTHWARD OVER SOUTHWESTERN MONTANA,
FOLLOWING THE CIRCULATION MOVING INTO WYOMING.
AS THE SYSTEM CONTINUES EASTWARD TONIGHT, A FEW LINGERING SHOWERS
REMAIN POSSIBLE ACROSS SOUTHWESTERN MONTANA INTO SUNDAY MORNING AS
MOISTURE WRAPS AROUND ITS BACKSIDE. CLEARING SKIES FROM THE WEST
OVERNIGHT INTO SUNDAY MORNING MAY FAVOR FOG FORMATION IN
SOUTHWESTERN MONTANA VALLEYS. UPPER-LEVEL RIDGING WILL THEN REBUILD
ACROSS MONTANA AND THE NORTHERN ROCKIES BY SUNDAY AFTERNOON,
RETURNING PREDOMINANTLY SUNNY, WARMER, AND DRIER CONDITIONS TO THE
AREA.
A DRY WEATHER PATTERN WITH ABOVE-NORMAL TEMPERATURES IS EXPECTED
NEXT WEEK. BROAD-SCALE RIDGING WILL ATTEMPT TO BUILD WESTWARD ACROSS
THE CONUS WHILE TROUGHING PERSISTS OFF THE WEST COAST, MAINTAINING
UPPER-LEVEL HEIGHTS ABOVE AVERAGE UNDER A SOUTHWESTERLY FLOW REGIME.
HIGH TEMPERATURES IN THE UPPER 70S TO AROUND 80 ARE ANTICIPATED,
RUNNING ROUGHLY 10 DEGREES ABOVE EARLY-AUTUMN NORMALS.
- FORECAST CONFIDENCE & SCENARIOS:
AN AREA OF RAINFALL WITH EMBEDDED MODERATE TO LOCALLY HEAVY RATES
(0.2 TO 0.4 IN/HR) WILL INITIALLY FOCUS ALONG THE US-12 CORRIDOR
EARLY THIS MORNING. THIS PRECIPITATION IS EXPECTED TO LIFT NORTHWARD
TOWARD THE LITTLE BELT AND SNOWY MOUNTAINS LATER THIS MORNING BEFORE
TAPERING OFF. THE HEAVIEST RAINFALL ACCUMULATIONS ARE ANTICIPATED
OVER AND ADJACENT TO THE CASTLE, BIG BELT, AND ELKHORN MOUNTAINS,
THOUGH CONFIDENCE IS SOMEWHAT LOWER REGARDING HOW FAR NORTH HIGHER
AMOUNTS WILL REACH INTO THE LITTLE BELTS.
AVIATION
19/06Z TAF PERIOD
A BAND OF RAIN SHOWERS CONTINUE ACROSS SOUTHWEST AND CENTRAL MT
THROUGH THE DAY SATURDAY. THERE REMAINS SOME MODEL UNCERTAINTY IN
IF THIS BAND LIFTS MORE NORTH THIS MORNING/AFTERNOON INTO NORTH-
CENTRAL MT, WHICH COULD AFFECT RAINFALL AND PRECIPITATION TIMING
AT TAF SITES ALONG THE EDGE OF THIS BAND (KGTF & KBZN). THESE
SHOWERS WILL ALSO BRING THE THREAT FOR MVFR TO IFR CEILINGS FOR
SOUTHWEST MT TAFS THROUGH THE MORNING HOURS. WEAK CAPE LINGERING
THROUGH SATURDAY AFTERNOON WILL BRING AN ISOLATED THREAT FOR
LIGHTNING, BUT IT WILL BE A HIT OR MISS AT SOUTHWEST MT TAF SITES.
THIS RAIN BAND WILL BREAK DOWN THROUGHOUT THE AFTERNOON AND EARLY
EVENING HOURS. -WILSON
HYDROLOGY
OBSERVED 24-HOUR PRECIPITATION TOTALS HAVE REACHED UP TO
APPROXIMATELY 1.00” IN NORTHWEST BEAVERHEAD COUNTY, PRIMARILY FROM
YESTERDAY EVENING, WITH 0.50–0.75” MEASURED SO FAR ACROSS PARTS OF
JEFFERSON, BROADWATER, AND MEAGHER COUNTIES. ALTHOUGH THE RISK FOR
INTENSE RAINFALL RATES IS SUBSIDING, THE POTENTIAL FOR RUNOFF AND
DEBRIS FLOW NEAR BURN SCARS PERSISTS THROUGH THIS MORNING. TODAY,
ADDITIONAL RAINFALL UP TO AROUND 1.00” IS LIKELY (60–90% CHANCE) IN
PORTIONS OF JEFFERSON, BROADWATER, AND MEAGHER COUNTIES, WHERE
LOCALIZED 24-HOUR TOTALS NEAR OR EXCEEDING 2 INCHES REMAIN POSSIBLE
(30–50% PROBABILITY). AMOUNTS OF THIS MAGNITUDE REPRESENT A 1-IN-5
TO 10-YEAR RECURRENCE INTERVAL FOR THIS TIME OF YEAR AND COULD
TRIGGER MINOR URBAN AND RURAL FLOODING IN POOR-DRAINAGE AREAS.
PRELIMINARY POINT TEMPS/POPS
GTF 68 47 74 47 / 20 0 0 0
CTB 68 43 73 44 / 0 0 0 0
HLN 63 46 72 46 / 100 20 0 0
BZN 59 42 66 40 / 100 60 10 0
WYS 57 31 61 29 / 70 40 10 0
DLN 59 40 67 40 / 70 30 0 0
HVR 73 46 74 46 / 0 0 0 0
LWT 61 45 65 43 / 70 70 50 0
TFX WATCHES/WARNINGS/ADVISORIES
FLASH FLOOD WATCH THROUGH THIS EVENING FOR BIG BELT, BRIDGER AND
CASTLE MOUNTAINS-ELKHORN AND BOULDER MOUNTAINS-LITTLE BELT AND
HIGHWOOD MOUNTAINS.
FLOOD WATCH THROUGH THIS AFTERNOON FOR CANYON FERRY AREA-
GALLATIN VALLEY-HELENA VALLEY-MEAGHER COUNTY VALLEYS.
FLASH FLOOD WATCH THROUGH THIS AFTERNOON FOR NORTHWEST
BEAVERHEAD COUNTY.
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