AREA FORECAST DISCUSSION

 
 FXUS65 KMSO 242133
 AFDMSO
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE MISSOULA MT
 233 PM MST TUE NOV 24 2009
 
 .DISCUSSION...
 
 TONIGHT THROUGH WEDNESDAY...A SHORTWAVE WEATHER DISTURBANCE WILL
 CONTINUE ITS PROGRESSION EASTWARD THIS EVENING AND OVERNIGHT AS
 HIGH PRESSURE MOVES IN FROM THE WEST. NORTHWESTERLY FLOW ALOFT WILL
 BE THE DOMINANT FLOW OVER THE NORTHERN ROCKIES OVERNIGHT AND
 THROUGH WEDNESDAY WITH MODEL CROSS SECTIONS SUPPORTING ENOUGH LOW
 LEVEL MOISTURE AND OROGRAPHIC LIFT FOR LIGHT MOUNTAIN SNOW SHOWERS
 MAINLY NORTH. LOOKOUT PASS HAS BEEN THE MOST INFLUENCED BY THESE
 SHOWERS WITH OFF AND ON LOWERED VISIBILITIES. SOME DRIER AIR WILL
 BEGIN TO MOVE INTO THE AREA OVERNIGHT ALLOWING FOR THESE SHOWERS
 TO DECREASE BY WEDNESDAY MORNING. LOW LEVEL INVERSIONS WILL ALLOW
 FOR SOME FOG DEVELOPMENT WEDNESDAY MORNING WITH THE MAIN FOCUS
 BEING IN NORTH CENTRAL IDAHO AND NORTHWEST MONTANA.
 
 THURSDAY...HIGH PRESSURE AND A STABLE ATMOSPHERE SHOULD PREVAIL.
 HOWEVER THERE SHOULD BE ENOUGH HIGH CLOUDS TO KEEP FOG FROM
 BECOMING WIDESPREAD IN THE VALLEYS. FRIDAY AND SATURDAY...A TROUGH
 OF LOW PRESSURE SHOULD IMPACT THE REGION. THERE SHOULD BE
 SUFFICIENT MOISTURE AND ENERGY TO PRODUCE SOME SNOW...ESPECIALLY
 OVER THE HIGHER TERRAIN.
 
 IN THE EXTENDED PERIODS FROM SUNDAY THROUGH EARLY NEXT WEEK THERE
 IS AGAIN A LOT OF UNCERTAINTY. FOR INSTANCE...NEARLY ALL THE
 OPERATIONAL FORECAST GUIDANCE A DAY AGO SHOWED A RIDGE OF HIGH
 PRESSURE AND DRY CONDITIONS FOR EARLY NEXT WEEK. GUIDANCE TODAY
 SHOWS SOMETHING QUITE DIFFERENT WITH MOISTURE MOVING THROUGH A
 FLAT RIDGE OF HIGH PRESSURE SUNDAY FOLLOWED BY ANOTHER WEATHER
 SYSTEM LATE MONDAY INTO TUESDAY. WHAT TO DO? GIVEN THE
 UNCERTAINTY...HAVE ELECTED TO GO WITH A MORE CLIMATOLOGICAL
 FORECAST WITH SOME MENTION OF PRECIPITATION AND NEAR NORMAL
 TEMPERATURES.
 
 &&
 
 .AVIATION...AN EXISTING SHORTWAVE LOW PRESSURE TROUGH WILL KEEP
 LIGHT MOUNTAIN SNOW SHOWERS INTO THE OVERNIGHT TONIGHT. HIGH
 PRESSURE WILL BEGIN TO BUILD INTO THE REGION FROM THE WEST TONIGHT
 AND THROUGH WEDNESDAY...ALTHOUGH MODEL SOUNDINGS AND AREA CROSS
 SECTIONS SHOW LINGERING LOW AND MID-LEVEL MOISTURE. THIS MOISTURE
 WILL BE ENOUGH TO KEEP LOWERED CLOUD DECKS MAINLY THROUGH WESTERN
 MONTANA THROUGH WEDNESDAY MORNING BEFORE A DRIER AIRMASS MOVES INTO
 THE NORTHERN ROCKIES BY WEDNESDAY EVENING. 
 
 &&
 
 .AIR STAGNATION...A RIDGE OF HIGH PRESSURE WILL BUILD OVER
 NORTH CENTRAL IDAHO AND WESTERN MONTANA TONIGHT AND THEN PERSIST
 THROUGH THURSDAY. THIS WILL SUPPORT A STABLE ATMOSPHERE...ESPECIALLY
 IN THE VALLEYS. A WEATHER SYSTEM AND ASSOCIATED COLD FRONT SHOULD
 MOVE ACROSS THE AREA FRIDAY AND SIGNIFICANTLY INCREASE THE LOWER
 ATMOSPHERE MIXING.
 
 &&
 
 .MSO WATCHES/WARNINGS/ADVISORIES...
 MT...NONE.
 ID...NONE.
 &&
 
 

 
 SHORT TERM...KITSMILLER
 LONG TERM....BAUCK
 AVIATION...KITSMILLER