555  
FXUS65 KTFX 220312  
AFDTFX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREAT FALLS MT  
812 PM MST SAT DEC 21 2024  
   
KEY MESSAGES  
 
- LIGHT MOUNTAIN SNOW AND LOWER ELEVATION RAIN ARRIVES LATE  
TONIGHT AND INTO SUNDAY MORNING.  
 
- BREEZY TO GUSTY WINDS ARE EXPECTED ALONG THE PLAINS NEXT WEEK,  
PARTICULARLY SUNDAY AND MONDAY.  
 
- THERE'S A SLIGHT CHANCE FOR LIGHT FREEZING RAIN NORTH OF THE  
HAVRE TO HARLEM LINE EARLY SUNDAY MORNING.  
 
- DAILY CHANCES FOR LIGHT MOUNTAIN SNOW NEXT WEEK, WITH LOWER  
ELEVATION MIXED PRECIPITATION CHRISTMAS EVE INTO CHRISTMAS  
MORNING.  
 
 
   
UPDATE  
 
THE MAIN CHANGE WITH THE EVENING UPDATE WAS TO BUMP UP THE START  
TIME OF THE WINTER WEATHER ADVISORY FOR HILL AND NORTHERN BLAINE  
COUNTIES. LIGHT RADAR RETURNS ARE MAKING THEIR WAY NORTHEASTWARD  
FROM CENTRAL MONTANA. ALTHOUGH LITTLE PRECIPITATION HAS BEEN  
OBSERVED SO FAR, I DIDN'T SEE A REASON TO RISK NOT HAVING THE  
ADVISORY IN EFFECT GIVEN COLD SURFACES. OVERALL, A LIGHT GLAZE  
LOOKS MOST LIKELY, WITH ANY ICE RESULTING IN VERY SLICK SURFACES  
TONIGHT INTO EARLY SUNDAY.  
 
THE OTHER CONCERN THIS EVENING IS FOR A PERIOD OF STRONG WINDS  
TONIGHT INTO SUNDAY MORNING ALONG THE ROCKY MOUNTAIN FRONT AND  
ADJACENT PLAINS. LATEST FORECAST SOUNDINGS ARE SHOWING ~50KTS  
WITHIN THE STABLE LAYER AROUND CUT BANK. IT SEEMS REASONABLE THAT  
A MOUNTAIN WAVE WOULD BE ABLE TO DIRECT A STRONG GUST OR TWO  
TOWARD THE SURFACE TONIGHT. ALTHOUGH THIS IS THE CASE, THE  
PROBABILITY FOR A 50 KT GUST IS ONLY AROUND 50-60% IN CUT BANK.  
HENCE, I HAVE ELECTED TO ISSUE A SPECIAL WEATHER STATEMENT TO  
COVER THE FORECAST CONDITIONS, NOTING THAT AN ISOLATED GUST OF  
50KTS WILL BE POSSIBLE IN AND AROUND CUT BANK TONIGHT.  
 
NO OTHER CHANGES WERE MADE AT THIS TIME. -AM  
 
 
   
DISCUSSION  
 
/ISSUED 436 PM MST SAT DEC 21 2024/  
 
- METEOROLOGICAL OVERVIEW:  
 
THE REST OF THE AFTERNOON REMAINS DRY ACROSS THE REGION AS THE  
UPPER- LEVEL RIDGE SLOWLY EXITS TO THE EAST. AN UPPER-LEVEL TROUGH  
MOVES IN THIS EVENING, BRINGING LIGHT MOUNTAIN SNOW AND LOWER  
ELEVATION RAIN THROUGH SUNDAY MORNING. ALONG THE HI-LINE, WHERE  
SHALLOW COLDER AIR AT THE SURFACE SUNDAY MORNING, CAN ALLOW A  
BRIEF FEW HOUR WINDOW FOR LIGHT FREEZING RAIN. THIS WILL BE MAINLY  
NORTH OF U.S ROUTE 2 FROM THE HAVRE TO HARLEM CORRIDOR. STRONG  
WARM AIR ADVECTION WILL TRANSITION FREEZING RAIN TO RAIN SHORTLY  
AFTER. WITH THIS RIDGE BREAKDOWN COMES STRONGER WINDS ALONG THE  
ROCKY MOUNTAIN FRONT AND BREEZY WINDS ACROSS THE PLAINS.  
 
NEXT WEEK LOOKS TO BE A MORE ACTIVE PATTERN EFFECTING MOSTLY THE  
HIGHER ELEVATIONS. MULTIPLE DISTURBANCES MOVE THROUGH THE REGION,  
BRINGING LIGHT, MOUNTAIN SNOW/MIXED PRECIP AT LOWER ELEVATIONS,  
AND GUSTY WINDS TO THE PLAINS. BETTER CHANCES FOR WIDESPREAD  
PRECIPITATION ARRIVES ON CHRISTMAS EVE TO EARLY CHRISTMAS MORNING  
AND LATE FRIDAY NIGHT TO SATURDAY MORNING. DAILY MINOR  
ACCUMULATIONS OF SNOW ALONG MOUNTAIN PASSES WILL HAVE A MINOR  
IMPACT TO HOLIDAY TRAVEL. TEMPERATURES ALSO REMAIN WELL ABOVE  
AVERAGE THROUGH THE WEEK.  
 
- FORECAST CONFIDENCE & SCENARIOS:  
 
IN TERMS OF SNOW TODAY, MARIAS PASS HAS A 20-30% CHANCE FOR 3" OF  
SNOW. WITH THIS HIGHER END AMOUNT ONLY HAVING MINOR IMPACTS TO  
TRAVEL, I HAVE OMITTED FROM ISSUING A WINTER WEATHER ADVISORY. IN  
OTHER MOUNTAIN PASSES, MINOR SNOWFALL AMOUNTS THAT RANGE UP TO  
2" LIKELY. THROUGHOUT THE WEEK, THERE'S A 30-40% CHANCE FOR 2" OF  
SNOW AT PASS LEVEL DAILY, LEAVING TO MINOR ACCUMULATIONS/ TRAVEL  
IMPACTS. LATE FRIDAY TO EARLY SATURDAY MORNING, THERE'S A 30%  
CHANCE FOR AREAS ABOVE 7,000FT TO GETTING 4" OF SNOW.  
 
FOR THE WINDS SUNDAY AND MONDAY, VERTICAL PROFILE SOUNDINGS SHOW  
35-45KT WINDS MIXING DOWN AT THE CUT BANK AREA. ALONG THE  
IMMEDIATE ROCKY MOUNTAIN FRONT AREA, THERE'S A 40% FOR 70MPH WINDS  
IN ISOLATED AREAS. STRONG WINDS WILL LIKELY BORDER HIGH WIND  
CRITERIA. WITH LESS THAN 80% CONFIDENCE IN THESE WINDS EXCEEDING  
CRITERIA, I HAVE ALSO OMITTED HIGH WIND PRODUCTS AT THIS TIME.  
GUSTY WINDS CONTINUE THROUGHOUT THE WEEK, BUT ALL LOOK TO STAY  
BELOW HIGH WIND CRITERIA.  
 
I HAVE MEDIUM CONFIDENCE IN THE LIGHT FREEZING RAIN CHANCES FOR  
AREAS NORTH OF THE HAVRE TO HARLEM LINE SUNDAY MORNING. HIGHER-  
RES GUIDANCE GIVES A 20-40% CHANCE FOR 0.01" OF ICE. THIS WINDOW  
WILL BE BRIEF, SINCE TEMPERATURES WILL QUICKLY WARM ABOVE  
FREEZING IN THE MORNING, TRANSITIONING TO RAIN AND LEAVING  
ACCUMULATIONS LIGHT (UP TO A FEW ONE HUNDRETHS).-WILSON  
 
 
   
AVIATION  
 
22/00Z TAF PERIOD  
 
INITIAL CONCERNS THIS TAF PERIOD WILL BE FOR INCREASING WINDS ACROSS  
SOUTHWEST THROUGH NORTH-CENTRAL MONTANA. BRIEF INSTANCES OF LOW-  
LEVEL WIND SHEAR WILL BE POSSIBLE THIS EVENING AS WINDS ALOFT  
INCREASE BUT INITIALLY DO NOT MIX TO THE SURFACE. THE BREVITY OF  
THESE CONDITIONS HAS SWAYED ME TO NOT INCLUDE MENTION OF WIND SHEAR  
IN TAFS AT THIS TIME, HOWEVER. THE STRONGEST WINDS ARE FORECAST  
ALONG THE ROCKY MOUNTAIN FRONT AND ADJACENT PLAINS TONIGHT, WITH  
MOUNTAIN WAVE TURBULENCE A CONCERN THROUGH SUNDAY AFTERNOON.  
OTHERWISE THERE IS A VERY LOW-END CHANCE FOR PRECIPITATION THROUGH  
THE MORNING ACROSS THE REGION AT MOST TERMINALS. KHVR HAS THE BEST  
CHANCE FOR PRECIPITATION, WITH AROUND A 50% CHANCE FOR FREEZING RAIN  
AT TIMES TONIGHT. -AM  
 
REFER TO WEATHER.GOV/ZLC FOR MORE DETAILED REGIONAL AVIATION  
WEATHER AND HAZARD INFORMATION.  
 
 
   
PRELIMINARY POINT TEMPS/POPS  
 
GTF 36 48 33 51 / 30 10 0 0  
CTB 35 43 27 46 / 30 10 0 0  
HLN 31 45 29 47 / 50 0 0 20  
BZN 27 44 26 43 / 40 10 0 50  
WYS 18 32 20 34 / 40 10 40 90  
DLN 25 41 26 42 / 10 0 10 30  
HVR 26 42 24 44 / 70 10 0 0  
LWT 33 45 27 48 / 50 10 0 10  
 
 
   
TFX WATCHES/WARNINGS/ADVISORIES  
 
WINTER WEATHER ADVISORY UNTIL 8 AM MST SUNDAY FOR HILL COUNTY-  
NORTHERN BLAINE COUNTY.  
 
 
 
 
HTTP://WWW.WEATHER.GOV/GREATFALLS  
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