398
FXUS65 KTFX 171715
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1015 AM MST TUE DEC 17 2024
KEY MESSAGES
- WARM FRONT LIFTS THROUGH THE AREA ON WEDNESDAY, BRINGING SOME
BRIEF SNOW BEFORE HIGH WINDS DEVELOP IN THE LATE MORNING AND
AFTERNOON
- WINDS WILL BE STRONGEST ALONG THE ROCKY MOUNTAIN FRONT, BUT
WINDS OVER 60 MPH WILL BE POSSIBLE ACROSS MUCH OF NORTH CENTRAL
AND SOUTHWESTERN MONTANA
- GENERALLY WARMER AND TRANQUIL, IF BREEZY AT TIMES, WEATHER
EXPECTED THROUGH THE REST OF THIS WEEK AS RIDGING BUILDS IN,
THOUGH ACTIVE WEATHER MAY RETURN NEXT WEEK
UPDATE
MID-MORNING UPDATE (1000 AM): SATELLITE TRENDS INDICATE FOG IS
BECOMING LESS WIDESPREAD ACROSS REGIONS WHERE THE DENSE FOG
ADVISORY WAS IN EFFECT. HENCE, THE DENSE FOG ADVISORY WAS CANCELED
EARLY. THE MAIN UPDATE THIS MORNING WAS TO ADD A WINTER STORM
WARNING FOR THE NORTHERN ROCKY MOUNTAIN FRONT TONIGHT INTO
WEDNESDAY AND TO ADD HIGH WIND WARNINGS FOR MOST AREAS FOR
WEDNESDAY.
AN IMPRESSIVE MID LEVEL SHORTWAVE WILL EJECT EASTWARD OUT OF A
SLIGHTLY MORE BROAD TROUGH THIS EVENING, HEADING TOWARD THE
NORTHERN ROCKIES. MOST MOISTURE LOOKS TO BE LIMITED TO THE
NORTHERN PORTION OF THIS WAVE, HENCE IMPACTFUL SNOW LOOKS TO BE
LARGELY RESERVED FOR THE NORTHERN ROCKY MOUNTAIN FRONT. THIS WAVE
WILL ALSO HAVE POTENT MID LEVEL FLOW, WHICH WILL BE TRANSLATED TO
THE SURFACE, INITIALLY ALONG THE ROCKY MOUNTAIN FRONT AND ADJACENT PLAINS
LATE TONIGHT, SPREADING EASTWARD AND SOUTHWARD THROUGH THE DAY
WEDNESDAY. BLOWING AND DRIFTING SNOW WILL BE A CONCERN IN AREAS
IMMEDIATELY ADJACENT TO THE NORTHERN ROCKY MOUNTAIN FRONT, BUT
CONFIDENCE IS NOT HIGH THAT IT WILL EXTEND MUCH OUT ONTO THE
PLAINS GIVEN SURFACE TEMPERATURES ARE FORECAST TO RISE WELL INTO
THE 30S IF NOT INTO THE 40S AT THE ONSET OF STRONG WINDS. TRENDS
WILL NEED TO BE CLOSELY MONITORED FOR ADDITIONAL IMPACTS FURTHER
EAST ON THE PLAINS DURING THE DAY WEDNESDAY.
PROBABILISTIC GUIDANCE GIVES A GREATER THAN 50% CHANCE (MOSTLY
GREATER THAN 70%) CHANCE FOR 80 MPH GUSTS ALONG THE PLAINS
IMMEDIATELY ADJACENT TO THE ROCKY MOUNTAIN FRONT WEDNESDAY. IN
OTHER AREAS NORTH OF I-90 THE CHANCE FOR 58 MPH GUSTS IS MOSTLY
GREATER THAN 50%. HENCE, HIGH WIND WATCHES WERE UPGRADED TO A
WARNING, WITH VARIOUS START AND END TIMES, LARGELY STARTING
EARLIER FURTHER WEST, AND LATER FURTHER EAST. HIGH WIND WATCHES
WERE ADDED/REMAIN IN EFFECT FOR MOST AREAS SOUTH OF I-90 (MADISON
RIVER VALLEY WAS UPGRADED TO A WARNING).
MORE MINOR CHANGES WERE MADE TO THE FORECAST TODAY TO REDUCE
HIGHS, ESPECIALLY ACROSS THE PLAINS WHERE LOW CLOUDS LOOK TO
LINGER THROUGH THE DAY. NO OTHER CHANGES WERE MADE AT THIS TIME.
-AM
EARLY-MORNING UPDATE (745 AM): SATELLITE AND SURFACE OBSERVATIONS
ARE SHOWING FOG DEVELOPING THIS MORNING IN AREAS WHERE SKIES ARE
CLEARING IN WAKE OF LIGHT SNOW LATE LAST NIGHT AND EARLY THIS
MORNING. FOG IN MOST AREAS IS PATCHY IN NATURE, BUT AREAS ON THE
PLAINS ADJACENT TO THE ROCKY MOUNTAIN FRONT, IN CASCADE COUNTY,
AND IN RIVER VALLEYS OF GALLATIN COUNTY ARE SEEING THE FOG BE A
BIT MORE WIDESPREAD IN NATURE. HENCE, A DENSE FOG ADVISORY WAS
ISSUED FOR THESE AREAS THROUGH NOON. IN ADDITION TO REDUCTION IN
VISIBILITY, ELEVATED SURFACES SUCH AS BRIDGES MAY BECOME SLICK
WHERE FOG IS MOST DENSE GIVEN BELOW FREEZING TEMPERATURES.
ELSEWHERE, WHERE FOG IS MORE PATCHY IN NATURE, A SPECIAL WEATHER
STATEMENT HAS BEEN ISSUED TO DESCRIBE POTENTIAL IMPACTS. -AM
DISCUSSION
/ISSUED 749 AM MST TUE DEC 17 2024/
- METEOROLOGICAL OVERVIEW:
UPPER LEVEL RIDGING WILL BEGIN TO BUILD INTO THE AREA TODAY IN
THE WAKE OF A WEAK TROUGH THAT MOVED THROUGH OVERNIGHT. AS THIS
RIDGE BUILDS IN, EXPECT A FAIRLY QUIET WEATHER DAY ACROSS NORTH
CENTRAL AND SOUTHWESTERN MONTANA, THOUGH WEAK HIGH PRESSURE
SLIDING IN ACROSS THE PLAINS WILL KEEP THE PLAINS ON THE COOL SIDE
EVEN AS THE SOUTHWESTERN VALLEYS BEGIN TO WARM UP UNDER THE
RIDGE’S INFLUENCE.
THE RIDGE THAT BUILDS IN TODAY WILL NOT LAST LONG, AS A STRONG,
VIGOROUS SHORTWAVE TROUGH ROARS INTO THE AREA, ALONG WITH IT’S
ASSOCIATED JET STREAK. WHILE SOME LIGHT SNOWFALL (AND ISOLATED
FREEZING DRIZZLE) WILL BE POSSIBLE AS THE SYSTEM’S WARM FRONT
SURGES THROUGH THE AREA, THE BIGGER STORY WILL BE THE STRONG WINDS
ASSOCIATED WITH THIS SYSTEM (MORE ON THAT IN THE CONFIDENCE &
SCENARIOS SECTION). AFTER THIS SHORTWAVE, UPPER LEVEL RIDGING WILL
TAKE A FIRM HOLD ACROSS THE WESTERN CONUS, WHICH WILL RESULT IN
WARMING CONDITIONS AND GENERALLY QUIET WEATHER, THOUGH IT WILL BE
A BIT BREEZY AT TIMES. LOOKING INTO NEXT WEEK, THERE IS FAIRLY
GOOD AGREEMENT IN THE MODELS SUGGESTING A SLIGHTLY ACTIVE, BUT
STILL WARM, WEATHER PATTERN FOR AT LEAST EARLY NEXT WEEK HEADING
INTO CHRISTMAS.
- FORECAST CONFIDENCE & SCENARIOS:
FOR TODAY, CONFIDENCE IS HIGH IN A MOSTLY QUIET DAY, ASIDE FROM
SOME EARLY MORNING FOG AND ISOLATED LIGHT SNOW SHOWER BEFORE HIGH
PRESSURE SLIDES IN FROM THE NORTH.
WEDNESDAY WILL BE THE HIGHEST IMPACT PERIOD OF THIS FORECAST AS
HIGH WINDS IMPACT MOST OF THE AREA. CONFIDENCE CONTINUES TO
STEADILY INCREASE IN A SEASONABLY NOTABLE HIGH WIND EVENT, WITH
MANY AREAS OF NORTH CENTRAL AND SOUTHWESTERN MONTANA NOW HAVING A
50-70%+ CHANCE OF WIND GUSTS OVER 55 MPH, AND AREAS ALONG THE
ROCKY MOUNTAIN FRONT, JUDITH GAP, AND SOME OF THE RIDGES OF
SOUTHWESTERN MONTANA HAVING OVER A 50% CHANCE OF WIND GUSTS OVER
65 MPH, I HAVE ELECTED TO EXPAND THE EXISTING HIGH WIND WATCH TO
MUCH OF SOUTHWESTERN MONTANA, ALONG WITH SOME EXPANSION FURTHER
NORTH ACROSS THE PLAINS. SUPPORTING THIS DECISION ARE TWO THINGS:
EARLIER TIMING AND, IN TURN, ATMOSPHERIC PROFILES MORE FAVORABLE
TO THE TRANSPORT OF THE STRONGEST WINDS TO THE SURFACE THANKS TO
DAYTIME THERMAL MIXING STILL BEING IN PLAY. RECENT ATMOSPHERIC
PROFILES SUGGEST THAT MOST LOW ELEVATION AREAS WILL HAVE ABOUT
APPROXIMATELY A 3-4 HOUR WINDOW FOR WIND GUSTS OVER 60 MPH, NAMELY
BETWEEN NOON AND 4, WHEN THERMAL MIXING WILL BEGIN TO WEAKEN AS
THE SUN SETS. THIS WILL ALSO COINCIDE WITH THE ARRIVAL OF COOLING
ALOFT, WHICH WILL MAKE THE AIR ALOFT EVEN MORE READY TO MIX TO THE
SURFACE VIA MECHANICAL MIXING OF THE AIR. AS CONFIDENCE
INCREASES, I WOULD EXPECT THAT MOST AREAS SEE THE HIGH WIND
WATCHES UPGRADED TO HIGH WIND WARNINGS, THOUGH WE ARE JUST A BIT
OUTSIDE THE TIME WINDOW FOR THE UPGRADES. REGARDLESS OF WHAT
PRODUCT IS OUT AT THE END OF THE DAY TODAY, BE PREPARED FOR A VERY
WINDY DAY ACROSS NORTH CENTRAL AND SOUTHWESTERN MONTANA, AND
ENSURE THAT ANY LOOSE CHRISTMAS/HOLIDAY DECORATIONS ARE SECURED.
BEYOND WEDNESDAY, WITH UPPER LEVEL RIDGING BECOMING ENTRENCHED
ACROSS THE WESTERN US, EXPECT TEMPERATURES TO GRADUALLY WARM, WITH
LITTLE TO NO PRECIPITATION EXPECTED. THIS RIDGE WILL HOLD THROUGH
SATURDAY, THOUGH THERE ARE SOME INDICATIONS THAT OUR WEATHER COULD
BECOME A BIT MORE ACTIVE EARLY NEXT WEEK. LUDWIG
AVIATION
17/12Z TAF PERIOD
A WEAK DISTURBANCE WILL EXIT THE AREA THIS MORNING WITH LOW VFR TO
MVFR CEILINGS REMAINING ACROSS MUCH OF THE REGION THROUGH
WEDNESDAY MORNING. BY WEDNESDAY AFTERNOON, A STRONG DISTURBANCE
WILL ARRIVE BRINGING A CHANCE FOR SNOW AND STRONG WINDS WITH LOW-
LEVEL WIND SHEAR, MOUNTAIN WAVE TURBULENCE, AND MOUNTAIN
OBSCURATION POSSIBLE THROUGH AT LEAST WEDNESDAY EVENING.
NORTH-CENTRAL MONTANA (KCTB, KHVR): PERIODS OF IFR DUE TO SNOW
AND FOG WILL CONTINUE AT KHVR THROUGH 17/18Z. AFTER THAT, MVFR
CEILINGS WILL PERSIST THROUGH THE REMAINDER OF THE TAF PERIOD WITH
ANOTHER CHANCE FOR SNOW AFTER 18/10Z. LOW CLOUDS WILL PERSIST AT
KCTB THROUGH MUCH OF THE PERIOD WITH A CHANCE FOR SNOW AFTER
18/06Z.
CENTRAL MONTANA (KGTF, KHLN, KLWT): PERIODS OF FOG AND LOW CLOUDS
ARE EXPECTED AT KGTF AND KLWT THROUGH THE FIRST 6 HOURS OF THE
PERIOD WITH TEMPORARY REDUCTIONS INTO MVFR DURING THIS TIME. BY
17/20Z, LOW CLOUDS ARE EXPECTED TO LIFT GIVING WAY TO MID AND HIGH
LEVEL CLOUDS THROUGH THE REMAINDER OF THE PERIOD. WITH THE ARRIVAL
OF THE DISTURBANCE, THERE IS A CHANCE FOR SNOW AT BOTH LOCATIONS
AFTER 18/06Z. OTHERWISE, VFR CONDITIONS AND GENERALLY LIGHT WINDS
WILL PERSIST THROUGH THE ENTIRE PERIOD AT KHLN.
SOUTHWEST MONTANA (KBZN, KEKS): PERIODS OF LOW-VFR TO HIGH-MVFR
WILL PERSIST THROUGH THE FIRST 6 HOURS WITH MOUNTAIN OBSCURATION
POSSIBLE DURING THIS TIME. AFTER THAT, VFR CONDITIONS ARE EXPECTED
TO PERSIST THROUGH THE REMAINDER OF THE PERIOD. WINDS WILL PICK UP
AT KEKS AFTER 18/00Z WITH GUSTY WINDS ARRIVING BY 18/05Z. WINDS
WILL START TO PICK UP AT KBZN AFTER 18/12Z WITH GUSTY WINDS
ARRIVING AFTER THE END OF THE 12Z TAF PERIOD INTO WEDNESDAY
AFTERNOON. -THOR
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 23 16 52 21 / 20 40 20 10
CTB 17 10 45 14 / 30 50 40 10
HLN 37 26 52 29 / 20 30 40 10
BZN 36 21 49 22 / 10 20 30 10
WYS 30 16 32 13 / 50 60 60 20
DLN 37 24 46 20 / 20 10 20 0
HVR 19 5 42 6 / 30 50 60 30
LWT 27 14 48 18 / 30 30 30 20
TFX WATCHES/WARNINGS/ADVISORIES
WINTER STORM WARNING FROM 9 PM THIS EVENING TO MIDNIGHT MST
WEDNESDAY NIGHT FOR EAST GLACIER PARK REGION.
HIGH WIND WARNING FROM 2 AM WEDNESDAY TO MIDNIGHT MST WEDNESDAY
NIGHT FOR EAST GLACIER PARK REGION-EASTERN GLACIER, WESTERN
TOOLE, AND CENTRAL PONDERA-NORTHERN HIGH PLAINS-SOUTHERN HIGH
PLAINS-SOUTHERN ROCKY MOUNTAIN FRONT.
HIGH WIND WARNING FROM 5 AM WEDNESDAY TO MIDNIGHT MST WEDNESDAY
NIGHT FOR CASCADE COUNTY BELOW 5000FT-EASTERN PONDERA AND
EASTERN TETON-EASTERN TOOLE AND LIBERTY-GATES OF THE MOUNTAINS-
JUDITH BASIN COUNTY AND JUDITH GAP-MADISON RIVER VALLEY-UPPER
BLACKFOOT AND MACDONALD PASS-WESTERN AND CENTRAL CHOUTEAU COUNTY.
HIGH WIND WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY EVENING
FOR BEAVERHEAD AND WESTERN MADISON BELOW 6000FT-GALLATIN AND
MADISON COUNTY MOUNTAINS AND CENTENNIAL MOUNTAINS-NORTHWEST
BEAVERHEAD COUNTY-RUBY MOUNTAINS AND SOUTHERN BEAVERHEAD
MOUNTAINS.
HIGH WIND WARNING FROM 11 AM WEDNESDAY TO 5 AM MST THURSDAY FOR
BEARS PAW MOUNTAINS AND SOUTHERN BLAINE-FERGUS COUNTY BELOW
4500FT-HILL COUNTY-NORTHERN BLAINE COUNTY-SNOWY AND JUDITH
MOUNTAINS.
HIGH WIND WARNING FROM 11 AM WEDNESDAY TO MIDNIGHT MST WEDNESDAY
NIGHT FOR BIG BELT, BRIDGER AND CASTLE MOUNTAINS-CANYON FERRY
AREA-ELKHORN AND BOULDER MOUNTAINS-GALLATIN VALLEY-HELENA VALLEY-
LITTLE BELT AND HIGHWOOD MOUNTAINS-MEAGHER COUNTY VALLEYS-
MISSOURI HEADWATERS.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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