031
FXUS65 KTFX 181102
AFDTFX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
402 AM MST WED DEC 18 2024
KEY MESSAGES
- STRONG WINDS ACROSS MUCH OF THE REGION ARE EXPECTED THROUGH
THIS EVENING.
- HEAVY SNOW AND AREAS OF BLOWING AND DRIFTING SNOW ARE EXPECTED
TODAY ALONG THE NORTHERN ROCKY MOUNTAIN FRONT.
- MILD AND GENERALLY DRY CONDITIONS RETURN BY THE WEEKEND.
DISCUSSION
- METEOROLOGICAL OVERVIEW:
A FAST MOVING CLIPPER SYSTEM WILL DEVELOP AND EJECT ACROSS THE
STATE TODAY BRINGING PERIODS OF HEAVY SNOW TO THE NORTHERN ROCKY
MOUNTAIN FRONT AND VERY STRONG WINDS ACROSS MUCH OF STATE. BLOWING
AND DRIFTING SNOW WILL CONTINUE TO BE A CONCERN FOR THIS REGION AS
WINDS CONTINUE TO PICK UP THROUGH THE MORNING HOURS. STRONG WINDS
WILL SLOWLY SPREAD ACROSS MUCH OF THE STATE THROUGH THE LATE
MORNING INTO THE EARLY AFTERNOON MAKING FOR A DANGEROUS, AT TIMES,
SITUATION FOR HIGH-PROFILE VEHICLES TRAVELING IN THE AREA. DAYTIME
MIXING ALONG WITH A VORT MAX DEVELOPING ROUGHLY ALONG THE HWY 200
CORRIDOR WILL ALLOW FOR POTENTIALLY HIGH-END WINDS TO REACH THE
SURFACE FROM GREAT FALLS TO LEWISTOWN THIS AFTERNOON. WINDS WILL
SLOWLY START TO LET UP LATER IN THE EVENING AND THE STRONGEST
WINDS ARE EXPECTED TO DIMINISH BY MIDNIGHT. TOWARDS THE WEEKEND,
RIDGING WILL BUILD OVER THE WESTERN CONUS WHICH WILL KEEP THINGS
GENERALLY ABOVE NORMAL THROUGH THE START OF NEXT WEEK WITH PASSING
DISTURBANCES ALONG THE RIDGE WILL PERIODICALLY BRINGING SOME
RAIN/SNOW THE REGION DURING THIS TIME.
- FORECAST CONFIDENCE & SCENARIOS:
SNOW/FREEZING RAIN POTENTIAL TODAY: EVALUATING THE CHANCES FOR
FREEZING RAIN, THE PROBABILITIES REMAIN LESS THAN 40% FOR PORTIONS
OF THE HI-LINE EAST OF HAVRE. IN GENERAL, THE MAIN THREAT EXTENDS
FURTHER INTO NORTHEASTERN MONTANA BEYOND THE CWA AND, AS SUCH,
THERE IS NO IMPACTFUL THREAT EXPECTED AT THIS TIME. SO THE
DECISION WAS MADE TO HOLD OFF ON ISSUING ANY WINTER WEATHER
PRODUCTS.
WHEN LOOKING AT UPDATED SNOW AMOUNTS AND PROBABILITIES, THE
OVERWHELMING MAJORITY OF THE THREAT IS STILL CONFINED TO THE EAST
GLACIER PARK REGION THAT IS ALREADY UNDER A WINTER STORM WARNING.
THERE ARE PROBABILITIES ABOVE 60% FOR 3 INCHES OR MORE ALONG THE
SOUTHERN ROCKY MOUNTAIN ZONE, HOWEVER, MUCH OF THAT IS ABOVE PASS
LEVEL AND AWAY FROM IMPACT AREAS THAT WOULD NORMALLY RAISE
CONCERNS. AS A RESULT, THE DECISION WAS MADE TO KEEP THE WARNING
FOR THE NORTHERN ROCKIES THE SAME AND REFRAIN FROM ADDING ANY
ADDITIONAL PRODUCTS WITH THIS FORECAST.
HIGH WINDS: THERE IS STILL NEAR-UNANIMOUS AGREEMENT IN THE MODELS
FOR A WIDESPREAD HIGH WIND EVENT FOR CENTRAL AND NORTH-CENTRAL
MONTANA TODAY. THERE IS ALSO GROWING CONCERN FOR THE POTENTIAL OF
GUSTS ABOVE 70 MPH ACROSS PORTIONS OF THE SOUTHERN ROCKY MOUNTAIN
FRONT INTO CASCADE AND JUDITH BASIN COUNTIES. MOST OF THIS CONCERN
COMES FROM A JET STREAK COMING THROUGH THE AREA DURING THE MID-
AFTERNOON HOURS WHICH COULD HELP PRODUCE THE HIGHEST WIND GUSTS
RIGHT ALONG CENTRAL MONTANA.
THE MAIN CHANGE WITH THIS FORECAST UPDATE WAS ADDRESSING THE
PREVIOUS HIGH WIND WATCH. PROBABILITIES OF GUSTS OVER 50 MPH ARE
GENERALLY LESS THAN 60% FOR THE HIGHER ELEVATIONS AND LESS THAN
40% FOR MOST OF THE VALLEYS OF SOUTHWEST MONTANA, WITH THE
EXCEPTION OF ENNIS. WHILE GUSTY WINDS ARE STILL VERY MUCH A THREAT
THIS AFTERNOON, HIGH WINDS ARE NOT EXPECTED FOR BEAVERHEAD AND
WESTERN PORTIONS OF MADISON COUNTY. THUS, THE HIGH WIND WATCH FOR
MOST OF SOUTHWEST MONTANA WAS CANCELLED. THE EXCEPTION WAS THE
ZONE INCLUDING THE MADISON AND GALLATIN RANGES. THE SOUTHERN HALF
OF THE ZONE HAS A LESS THAN 50% PROBABILITY OF EXCEEDING 55 MPH.
BUT THE CONCERN STARTS AROUND BIG SKY AND ALONG THE NORTHERN HALF.
THERE IS A BIT OF CONCERN FOR THOSE TRAVELING BETWEEN BOZEMAN AND
BIG SKY ON US-191 AS WELL AS ANYONE RECREATING IN THE NEARBY
MOUNTAINS. WITH THE PROBABILITY OF WINDS OVER 55 MPH ABOVE 70% FOR
THE AREAS OF CONCERN, THE DECISION WAS MADE TO ADD THE MADISON
AND GALLATIN RANGE ZONE INTO THE HIGH WIND WARNING AND TIME MATCH
IT TO WHEN THE REST OF SOUTHWEST MONTANA INCLUDING THE I-90
CORRIDOR. -THOR
AVIATION
18/06Z TAF PERIOD
VFR CONDITIONS WILL PREVAIL AT THE KBZN, KEKS, KHLN, AND KLWT AND
KCTB TERMINALS DURING THIS TAF PERIOD. HOWEVER, AT THE KCTB TERMINAL
THERE IS A 20 - 30% CHANCE FOR SNOW BETWEEN 18/06Z AND 18/14Z AND A
20 - 30% CHANCE FOR A RAIN/SNOW MIX BETWEEN 18/15Z AND 18/21Z. THERE
WILL BE FOG AROUND THE KHLN AND KGTF TERMINALS FOR A LEAST THE NEXT
COUPLE OF HOURS. DETERMINISTIC AND PROBABILISTIC GUIDANCE DIFFER ON
WHEN THE WIND WILL SHIFT AND INCREASE ENOUGH TO CLEAR THE FOG. THERE
WILL ALSO BE LOW CEILINGS FOR AT LEAST THE NEXT COUPLE OF HOURS AT
THE KGTF TERMINAL. AT THE KHVR TERMINAL THERE WILL BE SNOW BETWEEN
18/11Z AND 18/13Z WHICH WILL REDUCE VISIBILITY TO IFR LEVELS. AT THE
KHVR TERMINAL THERE IS A 20% CHANCE FOR RAIN BETWEEN 19/00Z AND THE
END OF THIS TAF PERIOD. AT THE KLWT TERMINAL THERE IS A 20 - 30%
CHANCE FOR RAIN/SNOW BETWEEN 18/09Z AND 18/14Z AND BETWEEN 18/17Z
AND THE END OF THE TAF PERIOD. AT THE KGTF TERMINAL THERE IS A 10 -
30% CHANCE FOR RAIN AND SNOW BETWEEN 18/06Z AND 18/14Z. AT THE KHLN
TERMINAL THERE IS A 20% CHANCE FOR SNOW BETWEEN 18/07Z AND 18/10Z
AND A 20 - 30% CHANCE FOR RAIN BETWEEN 18/17Z AND 18/23Z. AT THE
KBZN AND KEKS TERMINALS THERE IS A 20 - 30% CHANCE FOR RAIN/SNOW
BETWEEN 18/19Z AND 18/23Z. ANOTHER BIG AVIATION CONCERN DURING THIS
TAF PERIOD IS STRONG TO VERY STRONG WINDS. THE STRONGEST WINDS WILL
OCCUR BETWEEN 12Z AND THE END OF THIS TAF PERIOD WITH THE STRONGEST
WINDS PEAKING THIS AFTERNOON. BY THE END OF THIS TAF PERIOD WINDS AT
THE KEKS, KGTF, AND KCTB TERMINALS WILL GUST UP TO 62 KTS. FROM 12Z
ON THROUGH THE END OF THE TAF PERIOD ACROSS ALL TERMINALS THERE WILL
BE LOW-LEVEL WIND SHEAR. DURING MOST THIS TAF PERIOD THERE WILL BE
MOUNTAIN OBSCURATION. DURING THE MAJORITY OF THIS TAF PERIOD THERE
WILL BE MOUNTAIN WAVE TURBULENCE. -IG
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION
WEATHER AND HAZARD INFORMATION.
PRELIMINARY POINT TEMPS/POPS
GTF 52 22 45 30 / 10 10 0 0
CTB 46 17 37 23 / 30 10 0 0
HLN 51 27 43 25 / 40 0 0 0
BZN 48 20 42 20 / 20 10 0 0
WYS 32 9 33 7 / 40 20 0 0
DLN 45 19 40 22 / 10 0 0 0
HVR 41 4 21 8 / 80 50 0 0
LWT 48 20 41 24 / 40 20 0 0
TFX WATCHES/WARNINGS/ADVISORIES
WINTER STORM WARNING UNTIL MIDNIGHT MST TONIGHT FOR EAST GLACIER
PARK REGION.
HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT 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 UNTIL MIDNIGHT MST TONIGHT 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 WARNING FROM 11 AM THIS MORNING 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 THIS MORNING TO MIDNIGHT MST
TONIGHT FOR BIG BELT, BRIDGER AND CASTLE MOUNTAINS-CANYON FERRY
AREA-ELKHORN AND BOULDER MOUNTAINS-GALLATIN VALLEY-GALLATIN AND
MADISON COUNTY MOUNTAINS AND CENTENNIAL MOUNTAINS-HELENA VALLEY-
LITTLE BELT AND HIGHWOOD MOUNTAINS-MEAGHER COUNTY VALLEYS-
MISSOURI HEADWATERS.
HTTP://WWW.WEATHER.GOV/GREATFALLS
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