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AREA FORECAST DISCUSSION

 
 FXUS66 KSTO 251716
 AFDSTO
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SACRAMENTO CA
 900 AM PST WED NOV 25 2009
 
 .DISCUSSION...
 UPPER LEVEL RIDGE OF HIGH PRESSURE OVER THE AREA THIS MORNING AND 
 WILL MOVE EAST DURING THE DAY. THIS WILL BRING ANOTHER NICE FALL DAY 
 TODAY WITH TEMPERATURES IN THE MID 60S TO LOWER 70S IN THE VALLEY TO 
 THE MID 50S TO MID 60S IN THE HIGHER ELEVATIONS. PATCHY FOG FROM 
 AROUND MARYSVILLE SOUTH THIS MORNING TO AROUND MODESTO IS STARTING 
 TO DISSIPATE AND SHOULD DIMINISH BY AROUND 10 AM. THIS MORNINGS LOW 
 TEMPERATURES GENERALLY IN THE MID TO UPPER 30S IN THE 
 VALLEY...EXCEPT RED BLUFF IS WARMER WITH THE NORTHERLY WINDS 
 CONTINUING OVERNIGHT FOR A LOW OF ONLY 45. MOUNTAIN LOW TEMPERATURES 
 GENERALLY VARIED FROM THE MID 30S TO 40S.  LOCALLY GUSTY NORTHEAST 
 WINDS IN THE SIERRA AGAIN THIS MORNING WITH SURFACE HIGH PRESSURE 
 OVER THE GREAT BASIN.   
 
 THE WEATHER PATTERN CHANGES TOMORROW WITH THE RIDGE SHIFTING TO THE 
 EAST AND A TROUGH APPROACHING THE WEST COAST. THE 12Z MODELS HAVE 
 THIS SYSTEM ENTERING INTERIOR NORTHERN CALIFORNIA EARLY FRIDAY 
 MORNING AND SPREADING SOUTHEAST ACROSS THE AREA BY NOON. THE 12Z GFS 
 HAS PRECIPITATION FURTHER SOUTH THAN THE 06Z RUN AND THAN THE 
 CURRENT FORECAST SO WILL PROBABLY BUMP UP POPS FOR FRIDAY AFTER LOOK 
 AT ALL 12Z MODELS. PRECIPITATION WATER AROUND A HALF TO 0.75 INCHES 
 WITH MOST OF THE PLUME STAYING ALONG THE COAST. DYNAMICS NOT REAL 
 STRONG WITH A 100 KT NORTH-SOUTH ORIENTED JET MOVING THROUGH NORTH 
 OF INTERSTATE 80 EARLY FRIDAY MORNING.  GFS IS COLDER WITH THIS 
 SYSTEM THAN THE NAM WITH 700 MB TEMPERATURES AROUND -4 AND 
 1000-500MB THICKNESSES AROUND 5520M COMPARED TO -2  AND 5500M, 
 RESPECTIVELY ON THE NAM AT 12Z FRIDAY. SNOW LEVELS WILL BE AROUND 
 5000 TO 6000 FEET...WITH LOCALLY LOWER LEVELS POSSIBLE.  THE HIGHER 
 MOUNTAIN PASSES MAY GET A FEW INCHES OF SNOW FRIDAY. RIDGE OF HIGH 
 PRESSURE BUILDS IN BEHIND THIS SYSTEM FOR DRIER AND WARMER WEATHER 
 FOR THE WEEKEND.  NORTH TO EAST WINDS ARE ALSO EXPECTED TO RETURN 
 OVER THE WEEKEND. 
 
 
 .PREVIOUS EXTENDED DISCUSSION (SUNDAY THROUGH WEDNESDAY)...
 HIGH AMPLITUDE RIDGE REBUILDS OFF THE WEST COAST SUNDAY AND SHIFTS 
 INLAND MONDAY. THE ECMWF FLATTENS THE RIDGE SOMEWHAT MONDAY AS A 
 SHORTWAVE MOVES BY TO THE NORTH...HOWEVER THE GEM AND GFS KEEP THIS 
 FEATURE TOO FAR NORTH TO HAVE ANY INFLUENCE ON THE RIDGE. 850MB 
 TEMPERATURES RECOVER TO THE 6C-9C RANGE AND SURFACE HIGH PRESSURE 
 OVER THE GREAT BASIN WILL CONTINUE THE PATTERN OF LOCALLY BREEZY 
 NORTH TO EAST WINDS. FOG SHOULD BE PATCHY AND LIMITED TO THE LATE 
 NIGHT AND EARLY MORNING HOURS IN PRONE AREAS. THIS PATTERN WOULD 
 FAVOR ABOVE NORMAL TEMPERATURES. THE MODELS AMPLIFY THE RIDGE WELL 
 NORTH INTO BRITISH COLUMBIA/YUKON BY TUESDAY...WITH VARYING AMOUNTS 
 OF SHORTWAVE ENERGY DROPPING DOWN THE BACK SIDE OF THE RIDGE. THE 
 18Z DGEX AND 12Z GFS FROM YESTERDAY WERE SUGGESTING THAT AN 
 UNDERCUTTING OF THE WESTERLIES COULD OCCUR TOWARD THE MIDDLE OF NEXT 
 WEEK...AND SEVERAL OF THE GFS ENSEMBLES SUPPORT THIS AS WELL. BUT 
 THE 06Z DGEX AND GFS HAVE BACKED AWAY FROM THIS. SG
 
 &&
 
 .AVIATION...
 HIGH PRESSURE ALOFT REMAINS IN PLACE OVER CALIFORNIA WITH SURFACE 
 HIGH PRESSURE OVER THE GREAT BASIN. AREAS MVFR CIGS VSBY IN FOG WILL 
 IMPACT KSMF...KSAC AND KMHR UNTIL 17Z THIS MORNING. OTHERWISE VFR 
 CONDITIONS EXPECTED BEYOND 18Z ALL AREAS. LOCAL E SFC WNDS G30-40KT 
 THIS MORNING ALONG W SLOPE OF THE SIERRA CANYONS. FOG MAY BE A 
 CONCERN AGAIN THU MORN.  JMC
 
 &&
 
 .STO WATCHES/WARNINGS/ADVISORIES...NONE. 
 
 &&
 
 

 
 
 
 
 
 

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