479  
FXUS65 KTFX 181648  
AFDTFX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREAT FALLS MT  
948 AM MST WED DEC 18 2024  
 
AVIATION SECTION UPDATED.  
   
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  
 
/ISSUED 453 AM MST WED DEC 18 2024/  
 
- 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  
 
18/18Z TAF PERIOD  
 
THE PRIMARY CONCERN THIS TAF PERIOD WILL BE FOR A PERIOD OF STRONG  
WINDS ACROSS THE REGION THROUGH THE REMAINDER OF THE DAY. AHEAD OF  
THE STRONG SURFACE WINDS, LLWS WILL BE COMMON ACROSS THE REGION.  
STRONG SURFACE WINDS WILL SLOWLY SPREAD ACROSS THE REGION THROUGH  
THE DAY TODAY, PEAKING THIS AFTERNOON AND EARLY EVENING. MOUNTAIN  
WAVE TURBULENCE, LLWS, LOW-LEVEL TURBULENCE AND ALL ASSOCIATED  
HAZARDS WILL BE POSSIBLE THROUGH 06Z OR SO. WINDS GRADUALLY DIMINISH  
THIS EVENING AND TONIGHT, LEADING TO MORE BENIGN VFR CONDITIONS  
HEADING INTO THURSDAY. MOUNTAINS WILL BE OBSCURED AT TIMES,  
ESPECIALLY ALONG THE CONTINENTAL DIVIDE. -AM  
 
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION  
WEATHER AND HAZARD INFORMATION.  
 
 
   
PRELIMINARY POINT TEMPS/POPS  
 
GTF 52 22 45 30 / 20 10 0 20  
CTB 46 17 37 23 / 30 20 0 20  
HLN 51 27 43 25 / 40 20 0 0  
BZN 48 20 42 20 / 20 10 0 0  
WYS 32 9 33 7 / 70 30 10 0  
DLN 45 19 40 22 / 10 0 0 0  
HVR 41 4 21 8 / 80 50 10 10  
LWT 48 20 41 24 / 40 40 10 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 CASCADE COUNTY  
BELOW 5000FT-EAST GLACIER PARK REGION-EASTERN GLACIER, WESTERN  
TOOLE, AND CENTRAL PONDERA-EASTERN PONDERA AND EASTERN TETON-  
EASTERN TOOLE AND LIBERTY-GATES OF THE MOUNTAINS-JUDITH BASIN  
COUNTY AND JUDITH GAP-MADISON RIVER VALLEY-NORTHERN HIGH PLAINS-  
SOUTHERN HIGH PLAINS-SOUTHERN ROCKY MOUNTAIN FRONT-UPPER  
BLACKFOOT AND MACDONALD PASS-WESTERN AND CENTRAL CHOUTEAU COUNTY.  
 
HIGH WIND WARNING UNTIL 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 UNTIL 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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