815
FXUS65 KTFX 210529
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1129 PM MDT WED MAY 20 2026
AVIATION SECTION UPDATED.
KEY MESSAGES
- WIDESPREAD RAIN SHOWERS TODAY, WITH SOME WEAK
THUNDERSTORMS POSSIBLE THIS AFTERNOON.
- A COLD FRONT WILL LOWER SNOW LEVELS DOWN TO AROUND 6000
FT TONIGHT, ALLOWING FOR LIGHT MOUNTAIN SNOW ACCUMULATION
THROUGH TOMORROW MORNING.
- WARM AND DRY CONDITIONS THURSDAY NIGHT THROUGH THE HOLIDAY WEEKEND.
- BREEZY CONDITIONS SUNDAY THROUGH TUESDAY, WITH THE
STRONGEST WINDS BEING IN SOUTHWEST MT.
- CHANCES FOR PRECIPITATION AND AFTERNOON THUNDERSTORMS RETURN
ON MONDAY.
DISCUSSION
/ISSUED 529 PM MDT WED MAY 20 2026/
- METEOROLOGICAL OVERVIEW:
WIDESPREAD RAIN SHOWERS WILL CONTINUE TODAY, WITH ENOUGH
INSTABILITY TO SUPPORT A FEW AFTERNOON THUNDERSTORMS. WHILE THESE
THUNDERSTORMS WILL GENERALLY BE WEAK IN NATURE, SOME OF THE
STRONGER CORES COULD CONTAIN BRIEF DOWNPOURS, GUSTY WINDS IN
EXCESS OF 40 MPH, AND SMALL HAIL. RAIN WILL REMAIN SHOWERY THROUGH
THIS EVENING, BEFORE BECOMING STRATIFORM DURING THE OVERNIGHT
HOURS. LINGERING RAINFALL WILL BE SHOWERY TOMORROW MORNING, BEFORE
PRECIPITATION CHANCES TAPER OFF TOMORROW AFTERNOON. A COLD FRONT
WILL MAKE ITS WAY THROUGH MONTANA TONIGHT, LOWERING SNOW LEVELS TO
AROUND 6000 FT AND ALLOWING FOR LIGHT MOUNTAIN SNOW ACCUMULATION.
THE EXCEPTIONS ARE THE GALLATIN AND MADISON MOUNTAINS, IN WHICH
ISOLATED AREAS COULD RECEIVE A FEW INCHES OF SNOW.
RIDGING BEGINS TO BUILD IN THE WEST CONUS TOMORROW EVENING, AND
CONTINUES THROUGH THE HOLIDAY WEEKEND. THIS WILL ALLOW FOR WARM
TEMPERATURES, DRY CONDITIONS, AND SUNNY SKIES TOMORROW EVENING
THROUGH MONDAY. WESTERLY FLOW ALOFT WILL HELP MIX DOWN THE STRONG
UPPER LEVEL WINDS TO THE SURFACE, ALLOWING FOR BREEZY CONDITIONS
SUNDAY AND MONDAY. TEMPERATURES WILL PEAK ON MONDAY, WITH MANY
LOCATIONS SEEING HIGHS IN THE UPPER 70S TO MID 80S.
THIS PEAK WILL BE CUT SHORT BY ANOTHER COLD FRONT EARLY NEXT
WEEK, CAUSING TEMPERATURES TO DECREASE. AN UPPER LEVEL TROUGH
MOVING WEST FROM THE OLYMPIC PENINSULA WILL BRING BACK CHANCES FOR
PRECIPITATION AND AFTERNOON THUNDERSTORMS STARTING MONDAY NIGHT.
IT WILL ALSO BRING INCREASED WINDY CONDITIONS, WITH WINDS BEING
THE STRONGEST IN SOUTHWEST MT. THE TROUGH WILL BRING UNSTABLE
SOUTHERLY FLOW, WHICH, COMBINED WITH LOW SURFACE PRESSURE AND
SUFFICIENT MOISTURE, WILL INCREASE CHANCES FOR SOME THUNDERSTORMS
TO BE STRONG TO SEVERE. HOWEVER, THE MODELS ARE STILL DIVIDED ON
THE TIMING, STRENGTH, AND EXACT POSITION OF THIS TROUGH, MAKING THE
SEVERITY OF THESE STORMS UNCERTAIN. -DZOMBA
- FORECAST CONFIDENCE & SCENARIOS:
WIDESPREAD RAIN SHOWERS ARE EXPECTED TO CONTINUE THROUGHOUT THE
DAY, WITH CHANCES FOR THUNDERSTORMS IN THE AFTERNOON/EVENING
HOURS. WHILE THESE THUNDERSTORMS ARE GENERALLY EXPECTED TO BE WEAK
IN NATURE, THERE MAY BE LOCALIZED INSTANCES OF GUSTY WINDS OVER
40 MPH, SMALL HAIL OR GRAUPEL, AND HEAVY DOWNPOURS OVER A QUARTER
INCH WITH THE STRONGER CORES.
THIS ACTIVITY WILL EXPAND IN COVERAGE AND BECOME MORE STRATIFORM
AS IT SLIDES SOUTHWARD INTO SOUTHWEST MT TONIGHT INTO THURSDAY
MORNING. H700 TEMPERATURES FALLING TO AROUND -4 TO -7C COMBINED
WITH LINGERING CONVECTIVE PROCESSES MAY DROP SNOW LEVELS AS LOW AS
5000 FT AT TIMES, THOUGH ACCUMULATING SNOW LOOKS TO PRIMARILY BE
CONFINED TO AREAS ABOVE 6000 TO 6500 FT AND EVEN HIGHER. SNOWFALL
AMOUNTS LOOK TO BE MOST SIGNIFICANT OVER THE NORTHERN PORTIONS OF
THE MADISON/GALLATIN RANGES WHERE THE PROBABILITIES FOR AT LEAST 3
INCHES OF SNOW OR MORE ARE CURRENTLY RUNNING ABOVE 70% TONIGHT
THROUGH THURSDAY MORNING. THE PROBABILITIES IN THIS AREA FOR AT
LEAST 4 INCHES OF SNOW ARE 60-70%, WHEREAS FOR AT LEAST 6 INCHES
OF SNOW ITS 20-30%. OTHER MOUNTAIN AREAS OF THE SOUTHWEST, ALONG
THE CONTINENTAL DIVIDE, AND OVER THE CENTRAL ISLAND RANGES WILL
GENERALLY SEE TRACE AMOUNTS UP TO AROUND AN INCH OR TWO ON THE
HIGH END. OVERALL, COLD AND WET OUTDOOR RECREATION WILL BE THE
PRIMARY IMPACT WITH THIS SYSTEM. TOTAL RAINFALL/LIQUID EQUIVALENT
AMOUNTS WILL GENERALLY RANGE BETWEEN A TENTH TO A QUARTER INCH FOR
MOST LOWER ELEVATION LOCATIONS WITH A SHARP DECREASING GRADIENT
TO JUST A FEW HUNDRETHS OR SO ALONG THE HI-LINE AND THE DRIER
SOUTHWEST VALLEYS ALONG AND WEST OF I15. OF COURSE RAINFALL
AMOUNTS IN EXCESS OF A HALF INCH WILL BE MORE COMMON FOR AREAS
OVER AND NEAR HIGHER TERRAIN. PRECIPITATION DIMINISHES AND BECOMES
MORE SCATTERED IN NATURE BY THURSDAY AFTERNOON. -RCG AND DZOMBA
AVIATION
21/06Z TAF PERIOD
IFR/MVFR/LOW-VFR CONDITONS WILL PREVAIL THROUGH 14-18Z THURSDAY
BEFORE IMPROVING TO MVFR/LOW-VFR, WITH ALL TERMINALS BECOMING VFR
BETWEEN 20/21 TO 21/03Z. SHOWER ACTIVITY WAS CONTINUING TO
DECREASE ACROSS NORTH CENTRAL AND PORTIONS OF CENTRAL MONTANA LATE
THIS EVENING, WITH SHOWER ACTIVITY EXPECTED TO PERSIST SOUTH OF A
KHLN TO KBZN LINE THROUGH 14-18Z THURSDAY. GIVEN THE RECENT
PRECIPITATION AND PARTIAL CLEARING SKIES THERE IS THE POTENTIAL
FOR PATCHY FOG TO DEVELOP NEAR SUNRISE ON THURSDAY, ESPECIALLY
OVER THE PLAINS OF CENTRAL AND NORTH CENTRAL MONTANA; HOWEVER,
LATEST PROBABILISTIC DATA SUPPORTS LESS THAN A 10% CHANCE OF THIS
OCCURRING AT ANY GIVEN TERMINAL. FOR NOW WE WILL MONITOR SATELLITE
TRENDS FOR FOG DEVELOPMENT AND AMEND ACCORDINGLY. - MOLDAN
PRELIMINARY POINT TEMPS/POPS
GTF 36 59 37 69 / 60 10 0 0
CTB 33 60 35 68 / 40 20 0 0
HLN 38 60 36 68 / 90 30 0 0
BZN 34 55 30 66 / 90 80 0 0
WYS 28 50 22 60 / 100 70 0 0
DLN 34 56 31 65 / 90 50 0 0
HVR 33 62 35 72 / 10 20 10 0
LWT 34 54 33 64 / 50 40 10 0
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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