AREA FORECAST DISCUSSION

 
 FXUS65 KMSO 050336
 AFDMSO
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE MISSOULA MT
 936 PM MDT SAT OCT 4 2008
 
 .UPDATE...MADE SOME MINOR TWEAKS TO POPS AND MAX RH FORECAST.
 
 
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 .DISCUSSION...THE SURFACE FRONT THAT BROUGHT A LINE OF SHOWERS AND
 ISOLATED THUNDERSTORMS TO THE NORTHERN ROCKIES THIS AFTERNOON
 AND EVENING IS NOW ALONG THE CONTINENTAL DIVIDE. THE ATMOSPHERE
 REMAINS UNSTABLE BEHIND IT AND SCATTERED RAIN AND MOUNTAIN SNOW
 SHOWERS WILL CONTINUE THROUGH SUNDAY MORNING.
 
 SHOWERS ARE EXPECTED TO TAPER OFF THROUGH THE DAY IN THE VALLEYS
 WITH OROGRAPHIC PRECIPITATION MAINLY CONFINED TO THE MOUNTAINS AS
 THE UPPER LEVEL TROUGH TRACKS OVER THE NORTHERN ROCKIES. WINDS
 WILL INCREASE ALONG THE CONTINENTAL DIVIDE SUNDAY AFTERNOON AND
 EVENING AS THE SURFACE PRESSURE GRADIENT TIGHTENS IN RESPONSE TO
 THE PASSAGE OF THE UPPER LEVEL TROUGH.
 
 
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 .AVIATION...AN UPPER LEVEL TROUGH POSITIONED OVER THE
 PACIFIC NORTHWEST WILL PRODUCE SCATTERED SHOWERS ACROSS WESTERN
 MONTANA AND NORTH CENTRAL IDAHO THROUGH SUNDAY EVENING. LOW
 CEILINGS AND MOUNTAIN OBSCURATIONS ARE EXPECTED TO IMPACT ALL
 AIRFIELDS IN THE AREA. SUNDAY AFTERNOON AND EVENING WESTERLY
 WINDS WILL BECOME GUSTY AT TIMES AS THE SURFACE PRESSURE GRADIENT
 TIGHTENS IN RESPONSE TO THE UPPER LEVEL TROUGH PASSAGE.
 
 
 &&
 
 .PREV DISCUSSION... /ISSUED 509 PM MDT SAT OCT 4 2008/ 
 
 DISCUSSION...ANOTHER UPDATE THIS AFTERNOON AND EVENING TO
 INCREASE WINDS ACROSS NORTH CENTRAL IDAHO...ESPECIALLY FOR
 GRANGEVILLE AND LOWER HELLS CANYON. SOUTHWEST WINDS HAVE
 INCREASED IN THIS REGION WITH GUSTS UP TO 30 MPH AHEAD OF A SURFACE
 FRONT WHICH WILL TRACK EASTWARD THIS EVENING. EXPECT WINDS TO
 DECREASE AROUND 9 PM. 
 
 PREV DISCUSSION... /ISSUED 418 PM MDT SAT OCT 4 2008/
 
 DISCUSSION...JUST A QUICK UPDATE THIS AFTERNOON TO ADD ISOLATED
 THUNDERSTORMS TO NORTHWEST MONTANA EARLY THIS EVENING AS A LINE OF
 SHOWERS WITH ISOLATED THUNDERSTORMS TRACKS NORTHEAST IN A LINE FROM
 THE NORTHERN CLEARWATER MOUNTAINS UP THROUGH THE IDAHO PANHANDLE.
 THUNDERSTORM POTENTIAL IS EXPECTED TO DECREASE BY LATER THIS
 EVENING.
 
 PREV DISCUSSION... /ISSUED 249 PM MDT SAT OCT 4 2008/
 
 DISCUSSION...A COOL AND UNSTABLE ATMOSPHERE WILL REMAIN OVER THE
 REGION THIS EVENING AS A TROUGH OF LOW PRESSURE OVER THE PACIFIC
 NORTHWEST MOVES OVER ID AND MT OVERNIGHT. WIDESPREAD SHOWERS WILL
 EXIST THIS EVENING WITH A SLIGHT CHANCE OF THUNDERSTORMS OVER THE SOUTHERN
 CLEARWATER AND BITTERROOT/SAPPHIRE MOUNTAIN RANGES. THE ATMOSPHERE
 WILL BEGIN TO SLOWLY STABILIZE AFTER MIDNIGHT...WITH SHOWERS
 DECREASING ESPECIALLY IN THE VALLEYS. SNOW LEVELS WILL DROP TO
 NEAR 6000 FEET IN NORTHWEST MT...WITH SOME LIGHT SNOW POSSIBLE
 OVER THE HIGHER PEAKS. A STRONG WEST TO NORTHWEST FLOW ALOFT WILL
 DEVELOP IN THE WAKE OF THE PASSING TROUGH ON SUNDAY. THIS PATTERN
 WILL FAVOR OROGRAPHIC OR MOUNTAIN SHOWERS WITH A DECREASING TREND
 OF SHOWERS IN THE VALLEYS BY AFTERNOON. A WEAK PASSING FEATURE
 WILL MOVE OVER NORTHWEST MT SUNDAY NIGHT...TO KEEP A SLIGHT CHANCE
 OF MOUNTAIN SHOWERS GOING OVERNIGHT. VALLEYS SHOULD BE PRIMARILY
 DRY SUNDAY NIGHT.
 
 MONDAY THROUGH WEDNESDAY...A BRIEF RIDGE OF HIGH PRESSURE WILL
 EXIT MONDAY EVENING AND GIVE WAY TO ANOTHER TROUGH EXPECTED TO
 BRING SHOWERS ACROSS THE REGION THROUGH WEDNESDAY MORNING. DURING
 THIS TIME...AN UPPER JET WILL NOSE INTO NORTHERN IDAHO AND
 NORTHWEST MONTANA AND CREATE RATHER WINDY CONDITIONS. LATEST GFS
 MODEL RUN WEAKENED THIS JET SLIGHTLY FROM PREVIOUS RUNS...BUT
 DECIDED TO INCREASE WINDS NONETHELESS FOR TUESDAY INTO
 WEDNESDAY...PARTICULARLY IN HIGHER ELEVATIONS.
 
 THURSDAY THROUGH SATURDAY...NEXT SYSTEM EXPECTED TO IMPACT THE
 NORTHERN ROCKIES WILL COME IN THE FORM OF A DEEP TROUGH OF LOW
 PRESSURE. TIMING ON THIS TROUGH IS A LITTLE OFF BETWEEN
 MODELS...BUT ARE IN AGREEMENT THAT THE SYSTEM WILL COOL
 TEMPERATURES QUITE A BIT AND BRING RAIN AND MOUNTAIN SNOW SHOWERS
 FOR THE BEGINNING OF THE WEEKEND. JUST HOW MUCH COOLING WILL OCCUR
 WILL HAVE TO BE MONITORED AS TIME PASSES. SNOW LEVELS AND MIN TEMPS
 REALLY WANT TO COOL SIGNIFICANTLY...BUT CONFIDENCE AT THIS TIME IS
 NOT HIGH ENOUGH YET TO GO AS COLD AS SOME MODELS HAVE BEEN HINTING
 AT.
 
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 .MSO WATCHES/WARNINGS/ADVISORIES...
 MT...NONE.
 ID...NONE.
 &&
 
 

 
 UPDATE...DEROSA
 PREVIOUS DISCUSSIONS...DEROSA/FELSCH/ALLEGRETTO
 AVIATION...DEROSA
 
 
 
 
 
 
 
 

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