296  
FXUS65 KMSO 202206  
AFDMSO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MISSOULA MT  
306 PM MST MON NOV 20 2017  
   
DISCUSSION
 
LATEST RADAR AND SATELLITE IMAGERY IS SHOWING A  
LINE OF MODERATE TO HEAVY SHOWERS EXTENDING FROM LOOKOUT PASS TO  
PENDLETON, OREGON. THIS LINE OF SHOWERS WILL BE THE MAIN CONCERN  
FOR TRAVEL IMPACTS THIS AFTERNOON AND EVENING. OVER THE NEXT 6  
HOURS, THIS LINE IS EXPECTED TO MOVE THROUGH CENTRAL IDAHO, THEN  
INTO WEST-CENTRAL MONTANA AND THEN INTO SOUTHWEST MONTANA. SNOW  
LEVELS ARE AROUND 4000-5000 FEET, SO MOST OF THE TRAVEL IMPACTS  
WILL BE OVER MOUNTAIN PASSES. TRAVELERS OVER MOUNTAIN PASSES  
SHOULD EXPECT SUDDEN CHANGES IN ROAD CONDITIONS AND VISIBILITY  
ACROSS ALL MOUNTAIN PASSES THROUGH THIS EVENING.  
 
PRECIPITATION WILL BEGIN TO TAPER OFF AROUND MIDNIGHT TONIGHT AND  
PARTIAL CLEARING SHOULD LEAD TO THE DEVELOPMENT OF FOG OR LOW  
STRATUS CLOUDS FOR TUESDAY MORNING ACROSS WESTERN MONTANA AND  
CENTRAL IDAHO. FOG COULD BECOME LOCALLY DENSE IN AREAS,  
ESPECIALLY ACROSS WEST-CENTRAL MONTANA AND CENTRAL IDAHO WHERE THE  
MOST CLEARING IS EXPECTED. FOR NORTHWEST MONTANA, LINGERING RAIN  
SHOWERS MIGHT LEAD TO POCKETS OF LIGHT FREEZING DRIZZLE OVERNIGHT,  
BUT CONFIDENCE IS LOW ON FREEZING DRIZZLE. MOST OF THE RAIN  
SHOWERS SHOULD EXIT THE REGION BY DAYLIGHT ON TUESDAY AND FOG  
DEVELOPMENT WILL BE POSSIBLE ACROSS NORTHWEST MONTANA AS WELL.  
 
SNOW LEVELS WILL BEGIN TO RISE LATE TUESDAY WITH AN ATMOSPHERIC  
RIVER IMPACTING THE REGION THROUGH THANKSGIVING. EVEN MOUNTAIN  
PASSES WILL RECEIVE RAIN, WITH MANY HIGH ELEVATION LOCATIONS  
SEEING OVER 1.5 INCHES OF RAIN IN A 48 HOUR PERIOD INCLUDING  
WEDNESDAY AND THURSDAY. SMALL STREAMS WILL RISE WITH INCREASED  
RUN OFF, AND PONDING OF WATER ON ROADS WILL BE AN ISSUE DUE TO  
RAIN AND MELTING SNOW IN SOME AREAS. HOWEVER, SINCE THE GROUND IS  
NOT FROZEN AND CURRENT FLOWS ARE LOW, THE CURRENT RAIN FORECAST  
IS NOT ENOUGH TO CAUSE SIGNIFICANT FLOODING CONCERNS AT THIS TIME.  
 
THURSDAY NIGHT, A STRONG COLD FRONT WILL COME THROUGH. CONFIDENCE  
IS MODERATE ON THE TIMING, HOWEVER, WHEN THIS FRONT DOES COME  
THROUGH, THE PRECIPITATION WILL DRASTICALLY DECREASE AS THE RAIN  
TURNS TO SNOW. AT THIS TIME, ONLY A FEW INCHES OF SNOW IS  
EXPECTED AT THE HIGHER ELEVATIONS, POTENTIALLY AFFECTING AREA  
PASSES FRIDAY MORNING. STRONG WINDS ARE EXPECTED WITH THIS FRONT,  
WITH GUSTS IN THE 50 AND 60 MPH RANGES POSSIBLE IN THE MOUNTAINS.  
THE STRONG WINDS ARE A RESULT OF GOOD MODEL AGREEMENT ON A STRONG,  
ROUGHLY 140 KNOT JET AND 60 KNOT WINDS AT 10,000 FEET ABOVE SEA  
LEVEL SUPPORTING THE FRONT WHEN IT COMES THROUGH.  
 
THE STRONG WINDS WITH THE FRONT ARE ALSO CAUSING SOME UNCERTAINTY  
IN THE PRECIPITATION AMOUNT FORECAST FOR THE VALLEYS THURSDAY  
EVENING INTO FRIDAY MORNING. WITH SUCH STRONG WINDS, IT IS  
POSSIBLE THE VALLEYS WILL BE DOWN-SLOPED AND GET VERY LITTLE  
PRECIPITATION ONCE THE STRONG WINDS ARRIVE.  
 
NEXT WEEKEND A RIDGE QUICKLY REBUILDS OVER THE CONTINENTAL DIVIDE,  
LEAVING CENTRAL IDAHO AND NORTHWEST MONTANA UNDER MOIST SOUTHWEST  
FLOW AGAIN. MOSTLY CLOUDY SKIES AND LIGHT RAIN FROM TIME TO TIME  
ARE EXPECTED OVER THE WEEKEND AND EARLY NEXT WEEK. SNOW LEVELS ARE  
EXPECTED TO RISE AGAIN QUICKLY NEXT WEEK SO MOST PRECIPITATION  
WOULD BE RAIN AGAIN.  
 

 
   
AVIATION
 
MODERATE TO HEAVY RAIN/GRAUPEL SHOWERS WILL BE MOVING  
ACROSS THE REGION THIS AFTERNOON AND EVENING. KMSO AND KBTM COULD  
SEE LOCALLY HEAVY SHOWERS AS A WEAK FRONT MOVES THROUGH THIS  
EVENING. MAIN IMPACTS WILL BE VISIBILITY REDUCTIONS AND LOW  
CEILINGS THROUGH THIS EVENING. PRECIPITATION WILL END AROUND  
MIDNIGHT TONIGHT AND PARTIAL CLEARING WILL LEAD TO FOG DEVELOPMENT  
ACROSS THE AREA. KMSO AND KGPI WILL SEE THE BEST CHANCE FOR FOG  
DEVELOPMENT AT AREA TERMINALS. WITH THE RECENT RAIN, THERE IS A  
CHANCE FOR DENSE FOG DEVELOPMENT AT KGPI AND KMSO FOR TUESDAY  
MORNING.  
 

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

 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MT Page
The Nexlab ID Page Main Text Page