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.
&&
.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.
&&
.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
