860  
FXUS65 KTFX 221024  
AFDTFX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREAT FALLS MT  
324 AM MST WED NOV 22 2017  
   
SYNOPSIS
 
 
GUSTY WINDS FOR MANY AND BALMY TEMPERATURES WILL PERSIST THROUGH  
THANKSGIVING. IN FACT, SOME RECORD HIGH TEMPERATURES WILL BE  
CHALLENGED THANKSGIVING AFTERNOON. PERIODS OF PRECIPITATION,  
MAINLY IN THE FORM OF RAIN, WILL AFFECT THE CONTINENTAL DIVIDE  
AND MOUNTAINS OF CENTRAL AND SOUTHWEST MONTANA THROUGH THE  
DAYLIGHT HOURS OF THE HOLIDAY, WHILE THE REMAINDER OF THE REGION  
SHOULD REMAIN DRY. GUSTY WINDS AND AN INCREASED POTENTIAL OF  
PRECIPITATION ARE EXPECTED REGION-WIDE THANKSGIVING NIGHT, AS A  
PACIFIC COLD FRONT SWEEPS THROUGH.  
 

 
   
DISCUSSION
 
 
TODAY...AN UNUSUALLY-STRONG HIGH PRESSURE RIDGE ALOFT WILL REMAIN  
OVER OUR REGION TODAY, WHILE A SUBTLE DISTURBANCE TRAVERSING THIS  
RIDGE WILL EXIT OUR CWA TO THE EAST THIS MORNING. BASED ON THE  
EXPECTATION OF A SHARP LEE SURFACE TROUGH AND BRISK WESTERLY FLOW  
ALOFT PERSISTING THROUGH DAYBREAK THIS MORNING, WILL ALLOW THE HIGH  
WIND WARNING FOR THE ROCKY MOUNTAIN FRONT AND EASTERN GLACIER COUNTY  
TO REMAIN IN EFFECT. WINDS WILL LIKELY BEGIN TO EASE SOMEWHAT LATER  
THIS MORNING REGION-WIDE AS THE LEE SURFACE TROUGH WEAKENS IN  
RESPONSE TO THE AFOREMENTIONED DISTURBANCE EXITING THE AREA.  
HOWEVER, IT WILL BE A BREEZY AND MILD DAY, WITH AFTERNOON HIGHS  
EXPECTED TO BE ABOUT 10-20 DEGREES ABOVE-NORMAL. WHILE MOST PLACES  
WILL BE DRY DUE TO THE CHINOOK EFFECT, PERIODS OF UPSLOPE  
PRECIPITATION WILL OCCUR ALONG THE CONTINENTAL DIVIDE AND THE  
MOUNTAINS OF CENTRAL AND SOUTHWEST MT. PLEASE SEE THE HYDROLOGY  
SECTION FOR FURTHER DETAILS REGARDING CONCERNS ALONG THE DIVIDE.  
 
TONIGHT THROUGH FRIDAY...THE ABNORMALLY-STRONG HIGH PRESSURE RIDGE  
ALOFT WILL PERSIST TONIGHT BEFORE BEING BROKEN-DOWN BY A PACIFIC  
TROUGH ON THANKSGIVING THROUGH EARLY FRIDAY MORNING. A COLD FRONT  
ACCOMPANYING THIS TROUGH ALOFT IS EXPECTED TO CROSS OUR CWA  
THANKSGIVING EVENING THROUGH THE PREDAWN HOURS OF FRIDAY MORNING.  
ANOTHER HIGH PRESSURE RIDGE ALOFT WILL THEN BUILD OVER OUR AREA  
LATER ON FRIDAY. BESIDES PERIODS OF UPSLOPE PRECIPITATION PERSISTING  
ALONG THE CONTINENTAL DIVIDE, ONE OR SEVERAL BANDS OF PRECIPITATION  
SHOULD ACCOMPANY THE COLD FRONTAL PASSAGE AND AFFECT MOST, IF NOT  
ALL, OF OUR REGION. THIS FRONTAL PASSAGE IS ALSO EXPECTED TO BE  
ACCOMPANIED BY A PERIOD OF VIGOROUS WINDS, WHILE STRONG DOWNSLOPE  
WINDS ARE POSSIBLE ALONG THE ROCKY MOUNTAIN FRONT DURING MUCH OF THE  
PERIOD. THUS, WE WILL CONTINUE TO MONITOR THE THANKSGIVING THROUGH  
FRIDAY MORNING TIME FRAME FOR THE NEED OF ADDITIONAL HIGH WIND  
HIGHLIGHTS. WELL ABOVE-NORMAL TEMPERATURES ARE EXPECTED TONIGHT AND  
ON THANKSGIVING, WHEN SOME RECORD HIGHS WILL BE CHALLENGED IN THE  
AFTERNOON. THE AFOREMENTIONED COLD FRONTAL PASSAGE WILL RESULT IN  
COOLER TEMPERATURES THANKSGIVING NIGHT AND FRIDAY. HOWEVER, READINGS  
ARE STILL EXPECTED TO BE ABOVE-NORMAL DUE, IN PART, TO THE FRONT'S  
PACIFIC ORIGIN.  
JASZKA  
 
FRIDAY NIGHT THROUGH WEDNESDAY...MEDIUM RANGE MODELS ARE IN FAIRLY  
GOOD AGREEMENT IN THE DEPICTION OF AN ACTIVE BUT RELATIVELY  
MILD/PROGRESSIVE WEATHER PATTERN THROUGH THE MIDDLE OF NEXT WEEK.  
PERIOD BEGINS WITH AN UPPER LEVEL RIDGE PROGRESSING EAST ACROSS THE  
WESTERN U.S. THIS WEEKEND. TEMPERATURES WILL WARM TO NEARLY 20  
DEGREES ABOVE SEASONAL AVERAGES SAT/SUN. BREEZY WEST WINDS ACROSS  
THE PLAINS ON SATURDAY WILL INCREASE ON SUNDAY AS WEAK SHORTWAVE  
MOVES UP AND OVER THE RIDGE THROUGH SOUTHERN ALBERTA, SENDING A WEAK  
AND MOSTLY DRY SURFACE TROUGH/FRONT ACROSS THE REGION SUNDAY  
AFTERNOON/EVENING. A LARGER SCALE UPPER LEVEL TROUGH THEN MOVES  
ONSHORE SUNDAY NIGHT AND PROGRESSES EAST ACROSS THE NORTHERN ROCKIES  
AND MT MONDAY/MON NIGHT. THIS WILL SEND A COLD FRONT ACROSS THE  
REGION MONDAY WITH COOLING TEMPERATURES AND LOWERING SNOW LEVELS  
THOUGH MONDAY NIGHT. MODELS ARE STILL SOMEWHAT AMBIGUOUS WITH  
SMALLER SCALE SHORTWAVE DETAILS WITHING THE TROUGH, BUT A PERIOD OF  
PRECIPITATION APPEARS LIKELY FOR MOST AREAS WITH THE PASSAGE OF THIS  
SYSTEM, THOUGH ITS QUICK MOVEMENT WILL LIKELY LIMIT PRECIPITATION  
AMOUNTS TO THE LIGHTER SIDE FOR MOST AREAS WITH MODELS TRENDING  
TOWARDS CENTRAL AND SOUTHWEST MT AS THE MOST LIKELY LOCATION FOR THE  
DEVELOPMENT OF BAND OF FRONTAL PRECIPITATION WHICH COULD INVOLVE  
RAIN CHANGING TO SNOW FOR LOWER ELEVATIONS. UPPER LEVEL RIDGE BUILDS  
BACK IN BEHIND THIS SYSTEM ON TUESDAY AND WEDNESDAY FOR DRIER  
CONDITIONS.  
HOENISCH  
 

 
   
HYDROLOGY
 
 
UPDATED 324 AM MST WEDNESDAY  
 
SNOW LEVELS WILL REMAIN ABOVE 8000 FEET THIS MORNING THROUGH LATE  
THANKSGIVING DAY. RAINFALL AMOUNTS OF 1 TO 2 INCHES ARE EXPECTED  
IN THE MOUNTAINS ALONG THE CONTINENTAL DIVIDE FROM THE CANADIAN  
BORDER SOUTHWARD ALONG THE ROCKY MOUNTAIN FRONT DURING THE SAME  
PERIOD. THIS RAIN WILL FALL ON A MOUNTAIN SNOWPACK WITH A SNOW  
WATER EQUIVALENT RANGING FROM 1.5 INCHES TO OVER 7 INCHES OF  
LIQUID. THE COMBINATION OF RAINFALL AND SNOWMELT WILL CAUSE  
INCREASED RUNOFF IN SMALL STREAMS AND CREEKS ALONG THE ROCKY  
MOUNTAIN FRONT AND ESPECIALLY IN GLACIER NATIONAL PARK. AS A  
RESULT, THERE IS A POTENTIAL DANGER FOR LOCALIZED FLASH FLOODING  
AND MUD SLIDES.  
MPJ/JASZKA  
 

 
   
AVIATION
 
 
UPDATED 0515Z.  
 
WESTERLY FLOW ALOFT AND PRIMARILY VFR EXPECTED NEXT 24-HOURS AS HIGH  
PRESSURE ALOFT BUILDS OVER THE AREA. ALSO, A SUBTLE, E'WARD-MOVING  
DISTURBANCE WILL EXIT THE REGION BY 18Z/WED. AT THE SURFACE, A WARM  
FRONT EXTENDS SE'WARD FROM JUST NORTH AND EAST OF KCTB TO JUST NORTH  
AND EAST OF KLWT. THIS FRONT WILL CONTINUE MOVING NE'WARD AND SHOULD  
EXIT NORTH-CENTRAL MT BETWEEN 06Z AND 09Z/WED. BEHIND THIS FRONT,  
GUSTY SOUTHWESTERLY WINDS ARE EXPECTED OVER NORTH-CENTRAL MT,  
ESPECIALLY ALONG/NEAR THE ROCKY MOUNTAIN FRONT. THIS INCLUDES KCTB.  
EXCEPT FOR THE MADISON VALLEY, INCLUDING KEKS, LIGHTER SURFACE WINDS  
ARE EXPECTED OVER SW MT. LASTLY, PATCHY BR MAY DEVELOP IN THE  
SHELTERED VALLEYS OF SW MT, SUCH AS THE HELENA VALLEY, AROUND  
12Z/WED.  
JASZKA  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
GTF 60 47 65 38 / 10 0 0 40  
CTB 55 41 62 36 / 10 0 10 30  
HLN 51 36 60 33 / 10 0 10 60  
BZN 53 35 60 30 / 20 10 0 60  
WEY 41 31 44 26 / 50 30 20 50  
DLN 57 37 61 31 / 20 10 10 50  
HVR 58 44 67 37 / 10 0 0 20  
LWT 58 46 64 35 / 10 0 0 30  
 

 
   
TFX WATCHES/WARNINGS/ADVISORIES
 
 
HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING EASTERN GLACIER...  
NORTHERN ROCKY MOUNTAIN FRONT...SOUTHERN ROCKY MOUNTAIN FRONT.  
 

 
 

 
 
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