004  
FXUS65 KMSO 081006  
AFDMSO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MISSOULA MT  
306 AM MST THU DEC 8 2022  
   
DISCUSSION
 
HIGH PRESSURE IS ESTABLISHED OVER THE NORTHERN  
ROCKIES THIS MORNING AS THE REGION LIES BETWEEN WEATHER SYSTEMS.  
WARM AFTERNOONS THE LAST FEW DAYS HAVE CAUSED SOME SNOW MELT AND  
MOISTENED UP THE BOUNDARY LAYER, SO WITH THAT MOISTURE AND THE  
STABLE CONDITIONS UNDER THE RIDGE VALLEY FOG HAS BECOME A CONCERN.  
THE FOG WILL BE SHORT LIVED AS THE NEXT WEATHER SYSTEM COMES AND  
MIXES THINGS UP TONIGHT.  
 
A FAST MOVING, NARROW TROUGH WILL CROSS THE REGION TONIGHT THROUGH  
FRIDAY. THIS SYSTEM WILL BE PRETTY MINOR IN TERMS OF SNOW ONLY  
LEAVING 4-6 INCHES IN THE CLEARWATER MOUNTAINS AND THE CABINET  
MOUNTAINS WITH GENERALLY LESS THAN AN INCH OF SNOW IN THE VALLEYS.  
 
RIGHT AFTER THE TROUGH MOVES THROUGH THE REGION MODELS CONTINUE TO  
AGREE VERY WELL ON A CLOSED LOW DIVING SOUTH ALONG THE U.S. WEST  
COAST AND MOVING EASTWARD THROUGH THE SOUTHWEST EARLY NEXT WEEK.  
THERE IS QUITE A BIT MORE UNCERTAINTY WITH THIS SYSTEM, WHICH IS  
TYPICAL OF CLOSED LOWS. MUCH OF THE STATISTICAL GUIDANCE (NBM) HAS  
BEEN GOING VERY LOW ON SNOW AMOUNTS BUT IS TRENDING UPWARD,  
WHEREAS SOME OF THE PHYSICAL MODELS (ECMWF, GFS) ARE SHOWING A  
BROAD CLOSED LOW TRACKING ACROSS SOUTHERN IDAHO AT 700 MB (ABOUT  
10,000 FEET). IF THOSE MODELS VERIFY WELL, WE WOULD EXPECT TO SEE  
MORE SNOW IN LEMHI COUNTY IDAHO AND BUTTE, MONTANA. CURRENT  
FORECASTS HAVE LESS THAN A 10 PERCENT CHANCE OF 5 INCHES OR MORE  
OF SNOW IN BUTTE, ANACONDA, AND SALMON FORE EARLY NEXT WEEK.  
 
ONCE THAT LARGE LOW PRESSURE SYSTEM MOVES BY SOME MODELS TRY TO  
BUILD IN ANOTHER WEAK RIDGE SIMILAR TO THE ONE WE HAVE NOW, WHILE  
OTHERS LEAVE AN ODD, SMALL SCALE LOW PRESSURE SYSTEM OVER THE  
COLUMBIA BASIN TO OUR WEST. NEITHER SET UP IS VERY GOOD FOR  
BRINGING MORE SNOW TO THE REGION.  
 

 
   
AVIATION
 
HIGH PRESSURE IS ESTABLISHED OVER THE NORTHERN ROCKIES  
THIS MORNING AS THE REGION LIES BETWEEN WEATHER SYSTEMS. WARM  
AFTERNOONS THE LAST FEW DAYS HAVE CAUSED SOME SNOW MELT AND  
MOISTENED UP THE BOUNDARY LAYER. THE MOIST BOUNDARY LAYER AND  
STABLE CONDITIONS UNDER THE RIDGE ARE CAUSING AN INCREASED RISK OF  
VALLEY FOG. TERMINAL KGPI HAS ALREADY REPORTED SOME FOG LAST  
NIGHT, HOWEVER, TERMINAL KMSO HAS KEPT A STEADY DRAINAGE WIND  
ALONG THE CLARK FORK RIVER MOST OF THE NIGHT, SO LITTLE IF ANY FOG  
IS EXPECTED THERE THIS MORNING. TONIGHT AND FRIDAY A FAST MOVING  
TROUGH WILL PREVENT FURTHER FOG BUT WILL ADD SOME LIGHT SNOW  
SHOWERS. OVERALL IMPACTS FROM THAT SYSTEM WILL BE MINOR.  
 

 
   
MSO WATCHES/WARNINGS/ADVISORIES
 
 
MT...NONE.  
ID...NONE.  

 
 

 
 
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