275  
FXUS65 KTFX 211106  
AFDTFX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREAT FALLS MT  
505 AM MDT SAT SEP 21 2019  
   
SYNOPSIS
 
 
RAIN SHOWERS WITH MOUNTAIN SNOW WILL DECREASE THIS MORNING, AS  
THE LOW PRESSURE TROUGH EXITS THE REGION TO THE EAST. A FEW LIGHT  
SHOWERS MAY THEN REDEVELOP OVER THE MOUNTAINS IN THE AFTERNOON AS  
SKIES BEGIN TO CLEAR, BUT TEMPERATURES WILL REMAIN BELOW NORMAL.  
HIGH PRESSURE WILL THEN BRING DRY CONDITIONS WITH NEAR NORMAL  
TEMPERATURES FOR SUNDAY. A SERIES OF DISTURBANCES WILL BRING  
STRONG WINDS AT TIMES MONDAY THROUGH WEDNESDAY WITH A CHANCE OF  
MAINLY MOUNTAIN PRECIPITATION, BEFORE A MUCH COOLER AND WETTER  
PATTERN MOVES IN TO END NEXT WEEK.  
 

 
   
DISCUSSION
 
 
TODAY THROUGH SUNDAY...  
 
THE LOW PRESSURE TROUGH AND ITS ASSOCIATED BAND OF RAIN AND  
MOUNTAIN SNOW EXTENDING FROM RAYNOLDS PASS AND WEST YELLOWSTONE  
NORTHEAST THROUGH BOZEMAN, THE LITTLE BELT MOUNTAINS AND LEWISTOWN  
WILL GRADUALLY MOVE EAST OF THE AREA THROUGH THIS MORNING.  
ADDITIONAL WET SNOWFALL IN THE MOUNTAINS ABOVE 8000 FEET WILL  
LIKELY BE IN THE 1 TO 3 INCH RANGE AND WILL NOT CAUSE SIGNIFICANT  
ADDITIONAL IMPACTS. WILL THEREFORE ALLOW THE WINTER WEATHER  
ADVISORY FOR MADISON AND GALLATIN COUNTIES TO EXPIRE AT 6 AM. IN  
THE COOLER AIR ALOFT ON THE BACK SIDE OF THE TROUGH AND NEAR THE  
TROUGH AXIS, THE AIRMASS IS WEAKLY UNSTABLE. THIS, COMBINED WITH  
THE NORTHERLY UPSLOPE LOW/MID LEVEL WIND, HAS CAUSED RAIN SHOWERS  
TO FORM OVER THE PLAINS OF NORTH CENTRAL MONTANA AFTER MIDNIGHT.  
THESE SHOWERS SHOULD ALSO DECREASE AND MOVE EAST OUT OF THE AREA  
THIS MORNING WITH THE TROUGH. SKIES SHOULD BECOME PARTLY CLOUDY  
THIS AFTERNOON WITH THE INFLUX OF DRIER AIR, BUT THE ADDED HEATING  
FROM THE SUNSHINE WILL HELP CAUSE A FEW LIGHT SHOWERS TO  
REDEVELOP OVER THE MOUNTAINS, MAINLY OVER CENTRAL AND SOUTHWEST  
MONTANA. HOWEVER, COOL AIR WILL REMAIN IN PLACE, AS HIGHS WILL  
RANGE FROM JUST BELOW NORMAL IN THE NORTH TO AROUND 15 DEGREES  
BELOW NORMAL IN THE SOUTHWEST. HIGH PRESSURE ALOFT WILL THEN MOVE  
INTO MONTANA TONIGHT INTO SUNDAY, WHICH WILL KEEP THE AREA DRY  
WITH NEAR TO SLIGHTLY ABOVE NORMAL HIGHS AND AN INCREASE IN  
WESTERLY WINDS. COULSTON  
 
SUNDAY NIGHT THROUGH WEDNESDAY...  
 
AN UPPER-LEVEL LOW PRESSURE TROUGH SPLITS AS IT APPROACHES MONTANA  
FROM THE WEST ON MONDAY, WHICH WILL KEEP TEMPERATURES CLOSE TO  
NORMAL WITH MAINLY MOUNTAIN SHOWERS AND GUSTY WESTERLY WINDS. OF  
PARTICULARLY CONCERN IS MONDAY EVENING THROUGH EARLY TUESDAY MORNING  
ALONG THE NORTHERN ROCKY MOUNTAIN FRONT, WHERE A FEW WIND GUSTS  
REACHING WARNING CRITERIA ARE POSSIBLE, SO THIS WILL NEED TO BE  
MONITORED. A BRISK WESTERLY FLOW ALOFT WILL THEN MOVE INTO THE AREA  
IN THE WAKE OF THE TROUGH FOR TUESDAY INTO WEDNESDAY, WHICH WILL  
CONTINUE BREEZY WESTERLY SURFACE WINDS OVER MUCH OF THE AREA WITH  
SLIGHTLY COOLER THAN NORMAL TEMPERATURES AND A CHANCE FOR LIGHT  
PRECIPITATION AT TIMES.  
 
THURSDAY THROUGH NEXT SATURDAY...  
 
LONG RANGE MODELS ARE NOW IN GREAT  
AGREEMENT ON A SIGNIFICANT PATTERN CHANGE TO MUCH COLDER AND WETTER  
BEGINNING SOMETIME THURSDAY. A STRONG COLD FRONT IS POISED TO MOVE  
SOUTH ALONG THE ROCKY MOUNTAINS AND ADJACENT PLAINS AND THROUGH THE  
ENTIRE STATE BY LATE THURSDAY INTO FRIDAY MORNING. A RAIN/SNOW MIX  
AT THE BEGINNING LIKELY QUICKLY BECOMES A WET SNOW FOR MANY, IF NOT  
ALL, LOCATIONS IN THE MOUNTAINS AND EVEN SOME PARTS OF THE ADJACENT  
HIGH-ELEVATION VALLEYS AND HIGH PLAINS DURING THIS TIME. HIGH  
TEMPERATURES ON FRIDAY AS OF NOW APPEAR TO STRUGGLE INTO THE 30S AND  
40S FOR MANY LOCATIONS; LOWS COULD FALL INTO THE 20S (MOUNTAINS) AND  
30S FOR MUCH OF THE AREA AT NIGHT. DETAILS ON PRECIPITATION AMOUNTS,  
INCLUDING SNOW ACCUMULATIONS, WILL BE HONED IN ON WITH FUTURE  
FORECAST SHIFTS LEADING UP TO THE MAJOR WEATHER PATTERN CHANGE.  
 

 
   
AVIATION
 
 
UPDATED 505 AM MDT SAT SEP 21 2019 (21/12Z TAFS)  
 
RAIN SHOWERS, MOUNTAIN SNOW, AND AREAS OF FOG/LOW CLOUDS WILL  
CONTINUE LOW VFR/MVFR CONDITIONS WITH MOUNTAIN OBSCURATION ACROSS  
MUCH OF THE AREA THROUGH AROUND 15Z. AFTER 15Z, CONDITIONS WILL  
GENERALLY IMPROVE TO VFR THROUGH 18Z AS SKIES BECOME MOSTLY CLEAR  
WITH SOME GUSTY WESTERLY WINDS AT TIMES, ESPECIALLY OVER THE PLAINS.  
WEAK INSTABILITY MAY DEVELOP WITH THESE CLEARING SKIES, WHICH MAY  
ALLOW ISOLATED SHOWERS TO FORM OVER THE MOUNTAIN AREAS AFTER 18Z.  
HIGH PRESSURE ALOFT BUILDING INTO THE AREA AFTER 00Z WILL KEEP SKIES  
MOSTLY CLEAR WITH LIGHT WINDS. COULSTON  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
GTF 64 43 74 48 / 60 10 0 10  
CTB 64 42 71 47 / 10 0 0 0  
HLN 62 40 73 44 / 60 0 0 20  
BZN 56 35 70 39 / 50 10 0 10  
WEY 47 25 58 27 / 50 40 0 10  
DLN 58 35 66 40 / 20 0 0 20  
HVR 68 42 77 47 / 10 10 0 10  
LWT 57 40 70 45 / 70 10 0 10  
 

 
   
TFX WATCHES/WARNINGS/ADVISORIES
 
 
WINTER WEATHER ADVISORY UNTIL 6 AM MDT EARLY THIS MORNING ABOVE  
8000 FEET FOR GALLATIN...MADISON.  
 

 
 

 
 
HTTP://WWW.WEATHER.GOV/GREATFALLS  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MT Page Main Text Page