AREA FORECAST DISCUSSION

 
 FXUS65 KMSO 222142
 AFDMSO
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE MISSOULA MT
 242 PM MST SUN NOV 22 2009
 
 .DISCUSSION...AN UPPER LEVEL TROUGH AND ASSOCIATED JET STREAM WILL
 CONTINUE TO INFLUENCE THE NORTHERN ROCKIES THIS EVENING AND
 OVERNIGHT. THE FIRST BATCH OF PRECIPITATION FROM THIS MORNING HAS
 MOVED EAST OF THE CONTINENTAL DIVIDE AND LEFT MUCH OF WESTERN
 MONTANA AND NORTH CENTRAL IDAHO IN A BRIEF LULL. HOWEVER...AS THE
 UPPER JET PUSHES THROUGH THE REGION THIS AFTERNOON...ANOTHER
 ROUND OF SNOW SHOWERS IS EXPECTED. THE MAIN FOCUS OF THIS ACTIVITY
 IS EXPECTED TO REMAIN GENERALLY OVER NORTH CENTRAL IDAHO AND ALONG
 THE IDAHO/MONTANA BORDER. WITH SNOW LEVELS DOWN TO ALL BUT THE
 LOWEST VALLEY FLOORS...EXPECT ACCUMULATING SNOW TO CONTINUE INTO
 THIS EVENING OVER THE AFOREMENTIONED AREAS. IN ADDITION...GUSTY
 SOUTHWEST TO WEST WINDS WILL CAUSE LOCAL AREAS OF BLOWING AND
 DRIFTING SNOW...CAUSING HAZARDOUS DRIVING CONDITIONS IN LOW
 VISIBILITY. SEVERAL WINTER WEATHER ADVISORIES REMAIN IN
 PLACE...PLEASE SEE WWW.WEATHER.GOV/MISSOULA FOR FURTHER INFORMATION.
 
 THE MAIN UPPER TROUGH WILL SHIFT EAST OF THE CONTINENTAL DIVIDE
 OVERNIGHT TONIGHT...LEAVING NORTHWESTERLY FLOW ALOFT OVER THE
 NORTHERN ROCKIES. THIS FLOW REGIME WILL USHER A FEW WEAK
 DISTURBANCES THROUGH THE FLOW AND ALLOW FOR THE CONTINUATION OF
 LIGHT SHOWERS THROUGH MONDAY. THE SHOWERS MAY BECOME BANDED IN
 NATURE BY TOMORROW MORNING.
 
 MONDAY NIGHT THROUGH THURSDAY NIGHT...A FAST MOVING PACIFIC STORM 
 SYSTEM IS ANTICIPATED TO GRAZE NORTHWEST MONTANA BETWEEN MONDAY 
 NIGHT AND TUESDAY MORNING. THE MOST SIGNIFICANT STORM FEATURES ARE 
 EXPECTED TO REMAIN NORTH OF THE CANADIAN BORDER...HOWEVER UNSTABLE 
 NORTHWESTERLY FLOW AT RIDGETOP WILL LIKELY DEVELOP IN THE WAKE OF
 THIS SYSTEM. THE INSTABILITY WILL KEEP SNOW SHOWER ACTIVITY MAINLY
 LOCKED ON THE HIGH TERRAIN OF NORTHWEST MONTANA AND NORTH CENTRAL
 IDAHO. BY TUESDAY EVENING...HIGH PRESSURE WILL BECOME THE DOMINANT
 WEATHER FEATURE PRESENT ACROSS THE NORTHERN ROCKIES...WITH
 PRECIPITATION CHANCES DIMINISHING RAPIDLY THEREAFTER. VALLEY
 INVERSIONS WILL STRENGTHEN FROM TUESDAY NIGHT THROUGH
 THURSDAY...WITH RIDGETOPS AND MID SLOPES WARMING RAPIDLY.
 CONSIDERING RESIDUAL MOISTURE AND SNOW COVER EXPECTED TO BE
 PRESENT...FOG IS POSSIBLE WITHIN AREA VALLEYS DURING WEDNESDAY AND
 THURSDAY MORNINGS. LOW LEVEL MIXING WILL INCREASE BY THURSDAY
 EVENING AND ERODE MUCH OF THE AREA INVERSIONS...AS ANOTHER FAST
 MOVING SYSTEM APPROACHES THE REGION.
 
 FRIDAY THROUGH MONDAY...MEDIUM RANGE MODEL GUIDANCE IS ALL
 OVER THE MAP WITH POSSIBLE SOLUTIONS FOR THE REMAINDER OF THE
 FORECAST PERIOD. GENERALLY...THE UPPER LEVEL RIDGE WILL BEGIN TO
 SHIFT EAST INTRODUCING SOUTHWESTERLY FLOW AND POTENTIALLY BRING
 MIXING RELIEF TO FOG SOCKED VALLEY LOCATIONS. A PACIFIC TROUGH
 WILL SWING INTO THE NORTHWEST U.S. FRIDAY WITH THE POTENTIAL FOR
 SHOWER ACTIVITY TO ENCOMPASS THE REGION. THE GFS IS SHOWING A
 SLIGHTLY FASTER PROGRESSION OF THE SYSTEM AND CONCENTRATING
 PRECIPITATION CORES IN DIFFERENT LOCATIONS COMPARED TO THE ECWMF.
 THE FORECAST WAS ALREADY INDICATING A RETURN OF PRECIPITATION...SO
 KEPT THAT GOING. AFTER THE SYSTEM SETTLES INTO THE NORTHERN
 ROCKIES SATURDAY...THE GFS KICKS IT EAST WHILE THE ECWMF DIVES IT
 SOUTH INTO THE GREAT BASIN. BY THE END OF THE FORECAST PERIOD THE
 MODELS ARE OUT OF PHASE...SO TRENDED POPS SLIGHTLY TOWARDS
 CLIMATOLOGY AND MADE NO CHANGES TO TEMPERATURES UNTIL A MORE
 UNIFIED SOLUTION PRESENTS.
 
 &&
 
 .AVIATION...A PASSING UPPER LEVEL TROUGH WILL MAINTAIN LOW
 CEILINGS AND VISIBILITY THROUGH THE OVERNIGHT HOURS...CAUSING THE
 HIGHER TERRAIN TO REMAIN OBSCURED. SHOWER ACTIVITY WILL CONTINUE
 AREA WIDE THROUGH THE EVENING...BUT WILL BE MAINLY FOCUSED OVER
 NORTH CENTRAL IDAHO. SHOWER ACTIVITY IS EXPECTED TO GRADUALLY
 DECREASE IN INTENSITY AFTER 23/0600Z ALLOWING FOR AN IMPROVEMENT
 IN CEILING AND VISIBILITY.
 
 
 &&
 
 .MSO WATCHES/WARNINGS/ADVISORIES...
 MT...WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING FOR
      LOWER CLARK FORK REGION.
 
      WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING FOR 
      BITTERROOT/SAPPHIRE MOUNTAINS.
 
 ID...WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR 
      OROFINO/GRANGEVILLE REGION.
 
      WINTER WEATHER ADVISORY UNTIL 10 PM PST THIS EVENING FOR 
      NORTHERN CLEARWATER MOUNTAINS-SOUTHERN CLEARWATER MOUNTAINS.
 
 &&
 
 

 
 SHORT TERM...PALLISTER
 LONG TERM....ZUMPFE/NOLTE
 AVIATION...PALLISTER
 
 
 
 
 
 

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