826  
FXUS65 KMSO 221054  
AFDMSO  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MISSOULA MT  
354 AM MST TUE JAN 22 2019  
   
DISCUSSION
 
RECENT SNOW HAS COMBINED WITH A MELT-REFREEZE  
SITUATION ON AREA ROADWAYS, MAKING FOR VERY SLICK CONDITIONS  
ACROSS MUCH OF WEST CENTRAL AND NORTHWEST MONTANA THIS MORNING.  
EVEN THOUGH PRECIPITATION HAS ENDED, PLEASE USE CAUTION WHILE  
TRAVELING THIS MORNING.  
 
THE REGION'S NEXT ROUND OF WINTRY WEATHER WILL BEGIN TONIGHT, AS  
MOISTURE MOVES INTO THE NORTHERN ROCKIES FROM THE WEST. IN DOING  
SO, MODERATE TO HEAVY SNOWFALL WILL IMPACT MOUNTAINOUS TERRAIN  
ALONG THE ID/MT BORDER AND ALONG THE SPINE OF THE DIVIDE. AREA  
MOUNTAIN PASSES AND HIGH VALLEYS SHOULD ANTICIPATE DEGRADING  
TRAVEL CONDITIONS TONIGHT THROUGH THE ENTIRE DAY ON WEDNESDAY. AT  
THE SAME TIME, BACKCOUNTRY CONDITIONS WILL DETERIORATE QUICKLY,  
DUE TO STRONG RIDGETOP WINDS (GUSTING TO 40-50 MPH) ALONG WITH  
MODERATE TO HEAVY SNOW.  
 
BY WEDNESDAY MORNING, VALLEYS ACROSS NORTH CENTRAL IDAHO AND  
WESTERN MONTANA WILL BEGIN TO SEE SOME SNOWFALL, WHICH MAY MIX AT  
TIMES WITH RAIN ALONG AND SOUTH OF THE I-90 CORRIDOR THROUGH THE  
AFTERNOON HOURS. BY WEDNESDAY EVENING, THE COLD FRONT WILL CROSS  
THE REGION, DRIVING SNOW LEVELS BACK DOWN TO VALLEY FLOORS AND  
CHANGING PRECIP BACK OVER TO SNOW. DEPENDING ON HOW QUICK THIS  
TRANSITION OCCURS WILL DETERMINE JUST HOW MESSY WEDNESDAY  
AFTERNOON'S COMMUTE COULD GET (PARTICULARLY FOR LOCATIONS SUCH AS  
THE MISSOULA/BITTERROOT VALLEYS, WHERE THE RAIN-TO-SNOW TRANSITION  
ZONE WILL BE MOST NOTABLE).  
 
WEDNESDAY NIGHT THROUGH THURSDAY: LINGERING SNOW IN THE MOUNTAINS  
WILL CONTINUE, WHILE VALLEY SNOWFALL GRADUALLY TAPERS OFF THROUGH  
THURSDAY MORNING. WHEN IT'S ALL SAID AND DONE, A STORM TOTAL  
SNOWFALL AMOUNT ABOVE 4500 FEET WILL RANGE SOMEWHERE BETWEEN 10  
TO 14 INCHES OF NEW SNOW.  
 
THE EXTENDED RANGE OF THE FORECAST (FRIDAY THROUGH NEXT TUESDAY)  
WILL BE LARGELY DOMINATED BY THE PRESENCE OF TWO VERY STRONG  
WEATHER FEATURES SPREAD ACROSS NORTH AMERICA: AN AMPLIFIED HIGH  
PRESSURE RIDGE ALONG THE WEST COAST, AND AN ANOMALOUSLY DEEP  
TROUGH OF LOW PRESSURE EXTENDING FROM THE HUDSON BAY IN CANADA TO  
THE GULF OF MEXICO. THE RESULTANT NORTHWEST FLOW ALOFT IS OFT RIPE  
WITH WEAK WEATHER FEATURES THAT ARE VERY CHALLENGING FOR LONG  
RANGE MODELS TO ACCURATELY DECIPHER. THE FIRST FEATURE APPEARS TO  
QUICKLY PASS OVER THE NORTHERN ROCKIES FRIDAY, SPREADING LIGHT  
SNOW ABOUT THE AREA. THE FLOW APPEARS TO SETTLE SOME FOR THE  
WEEKEND, THOUGH THERE COULD STILL BE ADDITIONAL WEAK WEATHER  
SYSTEMS PASSING THROUGH THE FLOW THAT MODELS ARE NOT DEPICTING AT  
THIS TIME.  
 
A MORE ROBUST LOW PRESSURE TROUGH APPEARS TO ACCOMPANY A POLAR  
COLD FRONT AS IT PUSHES SOUTH OUT OF CANADA AND ACROSS THE PACIFIC  
NORTHWEST AND NORTHERN ROCKIES EARLY NEXT WEEK. WHILE THIS MAY NOT  
BE A FULL BLOWN 'ARCTIC' EVENT, THE AIR MASS EXCHANGE  
ACCOMPANYING THE COLD FRONT COULD BE RATHER STARK. AND YES, A  
PERIOD OF ADDITIONAL SNOWFALL SEEMS POSSIBLE AS WELL. THEREAFTER,  
NORTHWEST FLOW ALONG WITH LOW FORECAST CONFIDENCE RESUME AND  
PERSIST THROUGH AT LEAST MID WEEK.  
 

 
   
AVIATION
 
CLOUDS WILL BE STEADILY INCREASING THROUGHOUT THE DAY  
ACROSS THE REGION WHICH WILL HELP LIFT ANY FOG THAT HAS FORMED  
EARLIER THIS MORNING. OTHERWISE FEW ADDITIONAL AFFECTS WILL BE  
FELT BY THOSE WITH AVIATION INTERESTS THROUGHOUT THE AREA TODAY  
AND THIS EVENING. LIGHT SNOW WILL BEGIN TO FALL AT KGPI AFTER  
23/0800Z WITH THE POSSIBILITY OF LOWERED VISIBILITY AND CEILINGS  
HEIGHTS CONTINUING INTO WEDNESDAY MORNING. WIDESPREAD TERRAIN  
OBSCURATION WILL BE COMMON BY WEDNESDAY MORNING AS WELL.  
 

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

 
 

 
 
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