AREA FORECAST DISCUSSION

 
 FXUS65 KMSO 252113
 AFDMSO
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE MISSOULA MT
 213 PM MST WED NOV 25 2009
 
 .DISCUSSION...SURFACE AND UPPER RIDGE WILL BE CENTERED OVER THE
 INTERMOUNTAIN REGION TONIGHT THROUGH THURSDAY AFTERNOON. STILL
 HAVE SOME MOISTURE AND ENERGY STREAMING ACROSS THE APEX OF THIS
 UPPER RIDGE KEEPING CLOUDS OVER NORTHWEST MONTANA...MAINLY ALONG
 THE CANADIAN BORDER. TONIGHT LOOKS LIKE THE BEST POTENTIAL FOR FOG
 DEVELOPMENT ACROSS THE VALLEYS OF NORTH CENTRAL IDAHO AND WESTERN
 MONTANA...BUT HOW DENSE THE FOG IS WILL BE HIGHLY DEPENDENT ON
 SNOW ON THE GROUND...AND OR RECENT PRECIPITATION OVER THE AREA THE
 LAST 24 TO 36 HOURS. AT THIS TIME...VALLEYS ACROSS NORTHWEST
 MONTANA FROM NOXON TO KALISPELL AND WEST GLACIER AND POINTS NORTH
 ARE EXPECTED TO SEE FOG DEVELOP SHORTLY AFTER SUNSET...WHICH MAY
 BECOME DENSE DURING THE OVERNIGHT PERIOD. ALSO...HIGHER VALLEYS OF
 THE CLEARWATER MOUNTAINS WITH SNOW COVER...ELK CITY AND LOLO AND
 LOST TRAIL PASSES ARE EXPECTED TO SEE THE MOST FOG. OTHER VALLEY
 LOCATIONS OF NORTH CENTRAL IDAHO AND WESTERN MONTANA MAY STILL SEE
 FOG DEVELOPMENT TONIGHT...BUT SHOULD BE PATCHY IN NATURE.
 
 THE FOG WILL LINGER INTO THE EARLY AFTERNOON HOURS OF THANKSGIVING
 DAY...THEN GRADUALLY LIFT IN THE AFTERNOON AND EVENING AS AN
 APPROACHING PACIFIC WEATHER SYSTEM BEGINS TO INCREASE THE SURFACE
 PRESSURE GRADIENT AND RESULTANT WINDS. THIS PACIFIC WEATHER SYSTEM
 STILL LOOKS TO SPLIT ALONG THE WEST COAST WITH A WAVE DIVING INTO
 NORTHERN CALIFORNIA AND THE GREAT BASIN. MOISTURE AND LIFT
 ASSOCIATED WITH THE TROUGH LOOKS SUFFICIENT ACROSS THE
 INTERMOUNTAIN REGION FOR WIDESPREAD PRECIPITATION FRIDAY AND
 FRIDAY NIGHT. WARM...MOIST AIR AHEAD OF THIS SYSTEM WILL SPREAD
 PRECIPITATION IN THE FORM OF RAIN ACROSS NORTH CENTRAL IDAHO AND
 WESTERN MONTANA FRIDAY MORNING THEN SPREAD SOUTH AND EAST DURING
 THE DAY. AN ASSOCIATED COLD FRONT WILL SWEEP THROUGH FRIDAY
 EVENING LOWERING SNOW LEVELS TO MOST VALLEY FLOORS. WITH BRUNT OF
 PRECIPITATION AHEAD OF AND ALONG THE FRONT...ACCUMULATIONS ARE ONLY
 EXPECTED IN THE HIGHER TERRAIN AND THE MONTANA/IDAHO PASSES. AT
 THIS TIME...ACCUMULATIONS LOOK TO BE LESS THAN 5 INCHES OVER AN 18
 HOUR PERIOD OVER THE PASSES...AND A DUSTING IN THE VALLEYS.
 
 SATURDAY AND SUNDAY... THE NORTHERN ROCKIES WILL REMAIN UNDER
 THE INFLUENCE OF AN EXITING WEATHER SYSTEM WITH INCREASED SNOW
 CHANCES AGAIN SATURDAY. MOUNTAIN PASSES WILL LIKELY EXPERIENCE
 ACCUMULATING SNOWFALL THROUGH SATURDAY AND EVEN INTO SUNDAY.
 HOLIDAY TRAVELERS SHOULD MONITOR LATEST FORECASTS THROUGH THE END
 OF THE WEEK FOR POTENTIAL CHANGES AS THIS STORM SYSTEM DEVELOPS.
 
 MONDAY THROUGH WEDNESDAY...MODEL GUIDANCE HAVE COME INTO BETTER
 AGREEMENT WITH THE NEXT WEATHER PRODUCER PROJECTED TO ARRIVE TO THE
 PACIFIC NORTHWEST ON MONDAY AND THROUGH THE NORTHERN ROCKIES ON
 TUESDAY. THIS WEATHER SYSTEM LOOKS TO BE IN THE FORM OF A COLD LOW
 PRESSURE TROUGH WITH THE POTENTIAL FOR SNOW DOWN TO MOST VALLEY
 FLOORS... AND THE ADDITION OF A POTENTIALLY COLD AIRMASS. THE MAIN
 CHANGES TO THE FORECAST WERE TO INCREASE POPS ON TUESDAY AND
 DECREASE TEMPERATURES THROUGH THE MIDDLE OF THE WEEK.
 
 
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 .AVIATION...UPPER RIDGE BUILDING OVER THE INTERMOUNTAIN REGION
 WILL HELP STRENGTHEN INVERSIONS IN THE VALLEYS OF NORTH CENTRAL
 IDAHO AND WESTERN MONTANA. WITH MOSTLY CLEAR SKIES UNDER THIS
 RIDGE...POTENTIAL FOR FOG DEVELOPMENT STILL EXISTS...BUT THE AREAS
 THAT RECEIVED PRECIPITATION OVER THE LAST 36 HOURS...NORTHWEST
 MONTANA...ARE EXPECTED TO BE MOST IMPACTED. KGPI IS EXPECTED TO
 SEE LOW CEILINGS AND FOG DEVELOP THIS EVENING...THEN CONTINUE
 THROUGH THE NIGHT. REMAINING AIRFIELDS ARE ONLY EXPECTED TO SEE
 VICINITY FOG AND SCATTERED LOWER CLOUDS AS LOWER LEVELS ARE MUCH
 DRIER. 
 
 
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 .AIR STAGNATION...UPPER RIDGE WILL BE THE STRONGEST OVER THE
 INTERMOUNTAIN REGION TONIGHT THROUGH THURSDAY AFTERNOON.
 INVERSIONS WILL BE STRONGEST DURING THIS TIME WITH PARTICULATES
 TRAPPED IN THE VALLEYS. NEXT PACIFIC SYSTEM WILL MOVE ONTO THE
 WEST COAST THURSDAY EVENING. THIS APPROACHING WEATHER SYSTEM WILL
 INCREASE THE SURFACE PRESSURE GRADIENT AND BEGIN TO MIX OUT MANY
 OF THE VALLEYS...STARTING IN NORTH CENTRAL IDAHO IN THE
 EVENING...THEN INTO WESTERN MONTANA BY FRIDAY MORNING. 
 
 
 &&
 
 .MSO WATCHES/WARNINGS/ADVISORIES...
 MT...NONE.
 ID...NONE.
 &&
 
 

 
 SHORT TERM...MEAD
 LONG TERM....KITSMILLER
 AVIATION...MEAD