AREA FORECAST DISCUSSION

 
 FXUS65 KMSO 241028
 AFDMSO
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE MISSOULA MT
 328 AM MST TUE NOV 24 2009
 
 .DISCUSSION...A WEAK UPPER LEVEL LOW IS PASSING THROUGH CENTRAL
 ALBERTA THIS MORNING WILL DRAG A BROAD AREA OF MOISTURE AND
 GENTLE ATMOSPHERIC LIFT ALONG THE CANADIAN BORDER TODAY. FORECAST
 MODELS CONTINUE TO SHOW AN INCREASING CHANCE FOR LIGHT SNOW
 SHOWERS THROUGHOUT THE DAY. THIS APPEARS TO BE JUSTIFIED BY
 INCREASED CLOUD COVER OVER WASHINGTON EARLY THIS MORNING. THE GFS
 HAS BEEN FAR TOO BROAD WITH THE MOISTURE AND LIFT...THUS PREFER
 THE NAM AS IT SEEMS TO HAVE A GOOD HANDLE ON CURRENT CONDITIONS
 AND ITS FORECAST MOISTURE FIELDS APPEARS MUCH MORE REALISTIC.
 
 BY THIS EVENING A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD INTO
 THE PACIFIC NORTHWESTERN STATES. AS IT MOVES INLAND...THE LOWER/MIDDLE
 LEVEL CLOUDS AND ANY ASSOCIATED PRECIPITATION WILL BE SHIFTED INTO
 FAR NORTHWEST MONTANA. MODELS ARE SUGGESTING THAT LIFT MAY INCREASE
 BY EARLY WEDNESDAY MORNING BUT WITH LIMITED MOISTURE AND WARM AIR
 INCREASING ALOFT DUE TO THE BUILDING RIDGE...BELIEVE ANY
 ACCUMULATION WILL BE VERY LIGHT DUE TO LOW SNOW/LIQUID RATIOS.
 TEMPERATURES ALOFT WILL WARM AS THE RIDGE BUILDS INTO THE REGION
 WEDNESDAY. HOWEVER MOST OF THE LOWER VALLEYS WILL REMAIN QUITE
 COOL AND INVERTED THROUGHOUT THE DAY DUE PRIMARILY TO A VERY WEAK
 SURFACE PRESSURE GRADIENT AND NO APPRECIABLE WINDS.
 
 FORECAST MODELS ARE NOW LEANING TOWARDS A LESS AMPLIFIED AND
 WEAKER RIDGE OF HIGH PRESSURE COME THANKSGIVING DAY. GIVEN THAT
 THIS TREND APPEARS IN ALL MODELS...HAVE BACKED AWAY FROM AREAS OF
 FREEZING FOG TO FAVOR A MORE PATCHY SCENARIO. THERE DOES APPEAR TO
 BE ENOUGH DRY AIR IN THE MID LEVELS TO LIMIT THE AMOUNT OF MID
 LEVEL CLOUD COVER...HOWEVER HIGHER CLOUDS NOW APPEAR TO BE MORE
 POSSIBLE THUS GIVING ANOTHER LIMITING FACTOR TO FOG PRODUCTION.
 EVEN THOUGH A LONG LIVED FOG SITUATION DOES NOT APPEAR TO BE ON
 HAND...COOL TEMPERATURES CAN BE EXPECTED AS MOST VALLEYS WILL
 REMAIN INVERTED THROUGHOUT THE HOLIDAY.
 
 FRIDAY AND SATURDAY...BY EARLY FRIDAY MORNING THE BEGINNINGS OF
 THE NEXT WEATHER SYSTEM WILL TAKE AFFECT OVER THE NORTHERN
 ROCKIES. A WARM FRONTAL PUSH OF MOISTURE AND ASSOCIATED UPPER JET
 WILL CROSS WESTERN MONTANA AND CENTRAL IDAHO AND SPREAD
 PRECIPITATION ACROSS THE REGION THROUGH THE DAY. AS THE LOW
 PRESSURE CENTER RIDES JUST NORTH OF THE CANADIAN BORDER...IT WILL
 SWING A COLD FRONT THROUGH BY THAT EVENING...HELPING CONDITIONS TO
 TURN MUCH COLDER BEHIND THE SYSTEM AS IT EXITS SATURDAY MORNING.
 SHOWERS WILL CONTINUE AS UNSTABLE NORTHWEST FLOW TAKES OVER AND
 WILL KEEP A GENERALLY WET BUT MUCH COOLER FORECAST GOING.
 
 SUNDAY THROUGH EARLY NEXT WEEK...DIFFERENCES IN FORECAST MODELS
 LEAVE LITTLE CONFIDENCE IN HANDLING AN ADDITIONAL SHORTWAVE
 TROUGH THAT WOULD BRING MORE PRECIP TO THE NORTHERN ROCKIES ON
 SUNDAY. TIMING AND POSITION VARIES FROM MODEL TO MODEL...WITH A
 RIDGE OF HIGH PRESSURE BUILDING IN BEHIND. WITH SUCH
 DISCREPANCIES...VERY FEW CHANGES WERE MADE TO THE ONGOING FORECAST
 FOR THIS TIME PERIOD.
 
 
 &&
 
 .AVIATION...KMSO...KBTM AND KSMN ARE EXPECTED TO HAVE LITTLE IN
 THE WAY OF WEATHER IMPACTS THROUGH THE NEXT 24 HOURS AS HIGH
 PRESSURE GRADUALLY BUILDS ACROSS THE AREA. KGPI AND FLIGHT
 INTERESTS ACROSS NORTHWEST MONTANA CAN EXPECT LOWER CEILINGS AND
 WITH TERRAIN OBSCURATION IN CLOUDS AND PRECIPITATION TODAY AND
 TONIGHT.
 
 &&
 
 .MSO WATCHES/WARNINGS/ADVISORIES...
 MT...NONE.
 ID...NONE.
 &&
 
 

 
 SHORT TERM...DICKERSON
 LONG TERM....ALLEGRETTO
 AVIATION...DICKERSON
 
 
 
 
 
 
 
 

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