AREA FORECAST DISCUSSION

 
 FXUS65 KBOI 251617
 AFDBOI
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE BOISE ID
 917 AM MST WED NOV 25 2009
 
 .DISCUSSION...12Z BOI RAOB SHOWED THAT INVERSION HAS BECOME WELL 
 ESTABLISHED IN OUR VALLEYS AS WARMING CONTINUES ABOVE 850 MB WHILE 
 SURFACE COOLED SLIGHTLY SINCE 12Z TUESDAY.  THE COLD AIR IS STILL 
 DRY AND FOG HAS NOT DEVELOPED EXCEPT IN AND NEAR MYL.  FAIRFIELD 
 DIPPED TO -3F WHICH IS SIMILAR TO YESTERDAY AND MUCH COLDER THAN 
 ANYWHERE ELSE.  LITTLE CHANGE IN WX OVER OUR CWA IS EXPECTED THROUGH 
 THU NIGHT.  WEAK PACIFIC STORM WILL BRING LIGHT RAIN AND SNOW FRIDAY 
 ...BUT MORE IMPORTANTLY THE CURRENT AIR MASS WILL BE REPLACED WITH A 
 NEW CLEANER ONE.  GFS IS THE FASTEST MODEL ON FRIDAY/S PCPN...NAM IS 
 MUCH SLOWER...AND ECM IS BETWEEN GFS AND NAM.  AFTERNOON PACKAGE 
 WILL PROBABLY EXTEND CHANCE OF PCPN INTO FRIDAY NIGHT.  FOR NOW...
 NO UPDATES.
 
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 .AVIATION...VFR TODAY AND TONIGHT. STAGNATING CONDITIONS UNDER A 
 STRONG HIGH PRESSURE RIDGE WILL HAVE AN EFFECT ON VISIBILITY TODAY 
 THROUGH THURSDAY. INVERSION WILL BE AT ITS STRONGEST TODAY FOR 
 WIDESPREAD HAZE OVER THE LOWER VALLEYS. VSBY MAY REDUCE TO 5 TO 7SM 
 IN HAZE BEFORE LOW LEVEL EAST FLOW PICKS UP AHEAD OF APPROACHING 
 PACIFIC SHORT WAVE ON FRIDAY. SURFACE WINDS LIGHT TODAY AND TONIGHT 
 WITH LIGHT WINDS ALOFT IN CENTER OF UPPER RIDGE. 
 
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 .PREV DISCUSSION...
 SHORT TERM...TODAY THROUGH THANKSGIVING...BOTH THE UPPER LEVEL RIDGE 
 AND THE INVERSION INDEX MAX OUT OVER OUR AREA TODAY. THE SURFACE 
 HIGH PRESSURE CENTER STAYS ANCHORED OVER EASTERN IDAHO THROUGH 
 THURSDAY. THE GRADIENT STRENGTHENS ACROSS SOUTHWEST IDAHO AND 
 SOUTHEAST OREGON THURSDAY AFTERNOON...PROVIDING BETTER DOWN VALLEY 
 FLOW. THIS...COMBINED WITH A STEADILY DECREASING INVERSION 
 INDEX...WILL RESULT IN SLIGHTLY WARMER AFTERNOON TEMPERATURES.   
 SKIES WILL STAY MOSTLY CLEAR THROUGH TONIGHT...THEN HIGH CLOUDS WILL 
 INCREASE FROM THE WEST ON THURSDAY AS THE NEXT PACIFIC WEATHER 
 SYSTEM MOVES ONSHORE. 
 
 LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY...APPROACHING PACIFIC 
 SHORTWAVE WILL MOVE THROUGH THE REGION ON FRIDAY WITH VALLEY RAIN 
 AND MTN SNOW. LATEST MODEL QPF AMOUNTS ARE LIGHT WITH BAND OF HIGHER 
 PW GETTING CUT OFF AS SHORTWAVE MOVES ONSHORE. OVERALL PATTERN STAYS 
 PROGRESSIVE SO PRECIP NOT EXPECTED TO LINGER AND THUS SHOULD BE 
 LIGHT. A STRONGER RIDGE WITH MORE AMPLITUDE DEVELOPS OFFSHORE DURING 
 SATURDAY...BUT A SURGE OF MOISTURE COMES SOUTHEAST THROUGH THE AREA 
 SATURDAY AND SATURDAY NIGHT BEFORE THE RIDGE CRESTS IN. THIS MAY BE 
 THE LAST CHANCE FOR MEASURABLE RAIN OR SNOW IN NOVEMBER IN WHAT HAS 
 BEEN A DRY MONTH. DEPENDING ON HOW MUCH RAIN OR SNOW FALLS OVER THE 
 WEEKEND...THIS WILL ALSO HAVE IMPLICATIONS FOR INVERSION DEVELOPMENT 
 ALONG WITH LOW CLOUDS AND FOG IN A STRONGER RIDGE PATTERN SETTING UP 
 EARLY NEXT WEEK.    
 
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 .BOI WATCHES/WARNINGS/ADVISORIES...
 ID...NONE.
 OR...NONE.
 
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 WEATHER.GOV/BOISE
 
 DISCUSSION...LC
 AVIATION.....JS
 PREV SHORT TERM...JT
 PREV LONG TERM....GS