881
FXUS65 KTFX 181121
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
521 AM MDT THU JUN 18 2026
AVIATION SECTION UPDATED.
KEY MESSAGES
- SHOWER AND THUNDERSTORM ACTIVITY CONTINUES OVER CENTRAL AND
NORTH-CENTRAL MONTANA TODAY, WITH LOCALIZED GUSTY WINDS, BRIEF
DOWNPOURS, AND OCCASIONAL LIGHTNING BEING THE PRIMARY HAZARDS.
- DRIER AND WARMER CONDITIONS MOVE IN FOR FRIDAY AND MOST
OF SATURDAY, BUT SHOWERS AND THUNDERSTORMS WILL INCREASE FROM
SOUTHWEST TO NORTHEAST BY SATURDAY AFTERNOON.
- THERE WILL BE A SLIGHT COOLDOWN SUNDAY AND MONDAY BEFORE A MORE
SUMMERLIKE PATTERN WITH DAILY SHOWER AND THUNDERSTORM ACTIVITY
SETS UP DURING THE MIDDLE AND END OF NEXT WEEK.
DISCUSSION
/ISSUED 211 AM MDT THU JUN 18 2026/
- METEOROLOGICAL OVERVIEW:
A MOIST NORTHWESTERLY FLOW ALOFT WILL MAINTAIN SCATTERED TO
NUMEROUS SHOWERS AND THUNDERSTORMS FOR ANOTHER DAY. H500
TEMPERATURES DIP TO AS LOW AS -10C OVER THE PLAINS WITH A SHARP
TRANSITION TO WARMER AIR ALOFT SOUTH OF BOUNDARY THAT ROUGHLY RUNS
ALONG THE HIGHWAY 12 CORRIDOR. SHOWER AND THUNDERSTORM ACTIVITY
WILL BE MOST PRONOUNCED ALONG AND NORTH OF THIS BOUNDARY. WHILE
SURFACE CAPE VALUES WILL GENERALLY NOT EXCEED 500 J/KG, THE COOLER
AIR ALOFT, ITS ASSOCIATED FRONTOGENESIS, ALONG WITH ADDED SHEAR
FROM THE NORTHWESTERLY FLOW ALOFT ITSELF WILL BE SUFFICIENT FOR
INSTANCES OF LOCALIZED GUSTY WINDS, SMALL HAIL, AND BRIEF
DOWNPOURS IN ADDITION TO CLOUD TO GROUND LIGHTNING.
THIS ACTIVITY DECREASES IN COVERAGE LATER THIS EVENING AND
TONIGHT WITH THE LOSS OF DIURNAL HEATING AND THE COLDER AIR ALOFT
MOVING OFF TO THE EAST. WEAK TRANSIENT RIDGING DEVELOPS FRIDAY
INTO SATURDAY FOR A TEMPORARY WARMING AND DRYING TREND. HOWEVER,
BY SATURDAY MORNING, MONSOON MOISTURE AND SHORTWAVE ENERGY WILL
ALREADY SENDING WAVES OF SHOWERS AND THUNDERSTORMS INTO SOUTHWEST
MT. THIS ACTIVITY WILL MOVE NORTHEASTWARD INTO CENTRAL/NORTH-
CENTRAL MT BY LATE SATURDAY AFTERNOON AND EVENING. THIS ALL OCCURS
WHILE A PACIFIC TROUGH AND ATTENDANT COLD FRONT SWING IN FROM THE
NORTHWEST. GIVEN THESE PARAMETERS, SATURDAY AFTERNOON THROUGH
SATURDAY NIGHT WILL OFFER THE STRONGEST AND MOST WIDESPREAD SHOWER
AND THUNDERSTORM ACTIVITY. CAPE VALUES DON'T LOOK OVERLY
IMPRESSIVE AT THIS TIME, BUT THERE WILL BE POCKETS OVER 500 J/KG
AND PWAT VALUES WILL CREEP UP TO AROUND THREE QUARTERS OF AN INCH
OVER THE SOUTHWEST THANKS TO THE ADDED MONSOON MOISTURE.
THERE WILL BE A COOLDOWN AND ADDITIONAL OPPORTUNITIES FOR
ISOLATED SHOWERS AND THUNDERSTORMS SUNDAY INTO MONDAY WHILE THE
TROUGH AXIS TRAVERSES THE FORECAST AREA. MOST ENSEMBLES HIGHLIGHT
WEAK RIDGING ALOFT BRINGING A MORE SUMMERLIKE PATTERN FOR THE
MIDDLE AND END OF NEXT WEEK. TEMPERATURES LOOK TO CLIMB ABOVE
AVERAGE IN RESPONSE TO THE RIDGING, ALTHOUGH WEAK SHORTWAVES WILL
BRING DAILY OPPORTUNITIES FOR SCATTERED SHOWERS AND THUNDERSTORMS.
- RCG
- FORECAST CONFIDENCE & SCENARIOS:
SHOWER AND THUNDERSTORM ACTIVITY TODAY THROUGH SUNDAY...
THE MOST CONCERNING THUNDERSTORM DAYS WILL BE TODAY AND SATURDAY.
EVEN THOUGH THE CAPE WILL BE MODEST TODAY, THERE WILL BE
SUFFICIENT SHEAR AND FORCING FOR A FEW STRONGER STORMS. THIS
ACTIVITY WILL BE MOST WIDESPREAD OVER THE PLAINS EAST OF I15,
ALTHOUGH ANY CENTRAL/NORTH-CENTRAL LOCATION WILL BE SUSCEPTIBLE TO
AT LEAST ISOLATED STORMS. IMPACTS WILL BE GREATEST FOR OUTDOOR
RECREATION AND WILL INCLUDE LOCALIZED WIND GUSTS OVER 40 MPH,
SMALL HAIL, AND BRIEF DOWNPOURS IN ADDITION TO INSTANCES OF CLOUD
TO GROUND LIGHTNING.
SATURDAY'S SHOWER AND THUNDERSTORM ACTIVITY WILL INITIALLY BE
DRIVEN BY SHORTWAVE ENERGY AND MONSOON MOISTURE MOVING IN FROM THE
SOUTHWEST. THE ONE FACTOR THAT STANDS OUT WILL BE PWATS CREEPING
UP TO THE THREE QUARTER TO ONE INCH RANGE OVER SOUTHWEST AND
PORTIONS OF CENTRAL MT. THIS IS ABOUT ONE STANDARD DEVIATION ABOVE
CLIMATOLOGY PER THE NAEFS CLIMATE ANOMALY INDEX. SHOULD THIS
OCCUR, THEN LOCALIZED HEAVY DOWNPOURS CAPABLE OF PRODUCING
ISOLATED INSTANCES OF FLOODING IMPACTS TO NORMALLY FLOOD PRONE
AREAS SUCH AS BURN SCARS WILL BE PLAUSIBLE. CAPE VALUES DON'T LOOK
VERY IMPRESSIVE FOR WIDESPREAD STRONG TO SEVERE STORMS SATURDAY
AFTERNOON THROUGH SATURDAY NIGHT; HOWEVER, THIS COULD CHANGE,
PARTICULARLY IF THE TROUGH AND COLD FRONT MOVING IN FROM THE
NORTHWEST DEEPEN AND OFFER A MORE AMPLIFIED ARRIVAL. - RCG
AVIATION
18/12Z TAF PERIOD
NORTHWESTERLY FLOW ALOFT WILL BRING MORE PERIODS OF SHOWERS AND
THUNDERSTORMS OVER THE PLAINS THROUGH AT LEAST 19/00Z. MOST OF
THIS ACTIVITY SHOULD DIMINISH AND END BY AROUND 19/04Z WITH
PARTIAL CLEARING TAKING PLACE OVERNIGHT TONIGHT. THERE WILL BE
SOME MVFR CONDITIONS NEAR KCTB THROUGH AROUND 18/15Z AND THEN
BRIEF MVFR CONDITIONS MAY ACCOMPANY ANY SHOWER/THUNDER ACTIVITY
TODAY. INSTANCES OF PATCHY FOG CAN'T BE RULED OUT OVER THE PLAINS
TONIGHT, BUT CONFIDENCE WAS TOO LOW TO MENTION IN THE TAFS. - RCG
PRELIMINARY POINT TEMPS/POPS
GTF 69 45 74 49 / 60 20 0 0
CTB 64 41 70 47 / 50 20 0 0
HLN 77 46 80 51 / 10 10 0 0
BZN 79 43 81 49 / 10 0 0 0
WYS 75 36 81 44 / 0 0 0 0
DLN 80 43 82 50 / 0 0 0 0
HVR 69 42 73 49 / 70 20 0 0
LWT 66 40 71 46 / 70 20 0 0
TFX WATCHES/WARNINGS/ADVISORIES
NONE.
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