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AREA FORECAST DISCUSSION

 
 FXUS66 KMTR 241203
 AFDMTR
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
 403 AM PST TUE NOV 24 2009
 
 .DISCUSSION...AS OF 3:00 AM PST TUESDAY...LARGE SCALE SYNOPTIC
 PATTERN SHOWS FLAT RIDGE OVER CALIFORNIA WITH WEAK OFFSHORE FLOW AS
 HIGH PRESSURE BUILDS INTO THE GREAT BASIN BEHIND AN EXITING TROUGH
 THROUGH THE PLAINS.  A LARGE UPPER LOW IS COVERING MOST OF THE GULF
 OF ALASKA AND AND WILL BE THE NEXT WEATHER MAKER FOR THE PACNW AND
 NORTHERN CA.
 
 SKIES ARE MOSTLY CLEAR WITH JUST A FEW PATCHES OF DENSE FOG IN THE
 NORTH BAY...MAINLY NEAR SANTA ROSA.  A FEW HIGH CLOUDS ARE
 SPILLING OVER THE RIDGE INTO NORTHERN CA AND A FEW OF THESE MAY
 PASS QUICKLY OVER THE FAR NORTH THIS MORNING. TEMPERATURES ARE
 RUNNING IN SOME LOCATIONS 3 TO 5 DEGREES WARMER THIS EVENING AS THE
 OFFSHORE GRADIENT OF CLOSE TO 1 MB FROM SAC TO SFO AND OVER 10 MB
 FROM WMC TO SFO IS GENERATING SOME NE WINDS IN THE EAST BAY HILLS.
 WINDS OF 15 TO 25 KTS HAVE BEEN REPORTED AT ELEVATIONS ABOVE 1000
 FT.  WHERE THE WINDS ARE BLOWING TEMPERATURES ARE IN THE LOW 50S
 AND WHERE THESE WINDS ARE NOT BLOWING TEMPERATURES ARE IN THE MID 30S
 TO LOWER 40S.
 
 TODAY SHOULD BE MOSTLY SUNNY WITH A FEW DEGREES OF WARMING OVER
 YESTERDAY.  EXPECT HIGHS IN THE MID TO UPPER 60S NORTHERN HALF OF
 THE DISTRICT WITH UPPER 60S TO MID 70S SOUTHERN HALF.  THIS IS SOME
 5 TO 10 DEGREES ABOVE NORMAL.  EXPECT THIS CLEAR MILD WEATHER TO
 CONTINUE WITH EVEN A FEW MORE DEGREES OF WARMING FOR WEDNESDAY AS
 HIGH PRESSURE DOMINATES THE AREA.  MAY AGAIN SEE SOME PATCHY GROUND
 FOG IN PROTECTED LOW LYING AREAS FOR WED MORNING BUT MOSTLY IN THE
 NORTH BAY.  OFFSHORE WINDS SHOULD HELP KEEP FOG FROM DEVELOPING FOR
 MOST OF THE EAST AND SOUTH BAY AND MONTEREY BAY AREA.
 
 
 THANKSGIVING DAY WILL START OFF WITH JUST SOME PATCHY DENSE GROUND
 FOG IN THE NORTH BAY VALLEYS GIVING WAY TO INCREASING CLOUDS FROM
 THE NORTH AND WEST AS A WEAK COLD FRONT APPROACHES.  EXPECT JUST A
 SLIGHT CHANCE OF RAIN ALONG THE SONOMA COAST BY LATE THURSDAY WITH
 CHANCES INCREASING AND SPREADING SOUTH TO THE BAY AREA BY THURSDAY
 NIGHT.  THIS WILL BE A WEAK SYSTEM AND RAIN AMOUNTS WILL BE LESS
 THAN A TENTH OF AN INCH IN THE NORTH A MAYBE A FEW HUNDREDTHS AROUND
 THE BAY BY SUNRISE FRIDAY.  JUST A FEW LOW CLOUDS WILL DRIFT AS FAR
 SOUTH AS MONTEREY BAY FRIDAY MORNING WITH CLEARING SKIES IN THE
 NORTH.
 
 EXTENDED...ONCE THE WEAK COLD FRONT PASSES SKIES SHOULD CLEAR BY
 LATE FRIDAY MOST AREAS WITH HIGHS NEAR NORMAL.  A WARMING TREND
 WILL BEGIN FOR THE WEEKEND INTO EARLY NEXT WEEK AS MODELS NOW IN
 AGREEMENT THAT A RIDGE OF HIGH PRESSURE WILL DOMINATE THE WEST
 COAST THROUGH THE EXTENDED PERIOD.  THE LATEST ECMWF DOES SHOW A
 SECONDARY TROUGH DIGGING DOWN INTO THE GREAT BASIN ON SATURDAY THAT
 WOULD BRING BREEZY NORTH WINDS TO THE AREA SATURDAY WITH JUST
 SEASONAL TEMPERATURES WHILE THE GFS WOULD HAVE LESS WINDS AND
 MILDER TEMPERATURES FROM SATURDAY AS IT HAS THIS TROUGH FARTHER
 EAST.  EITHER WAY THE WEEKEND WILL BE SUNNY AND MILD AND THIS DRY
 WEATHER PATTERN WILL CONTINUE INTO EARLY NEXT WEEK.
 
 WEEK TWO AND BEYOND...THERE ARE TWO INTERESTING FEATURES THAT MAY
 BEGIN TO SHIFT THE LARGE SCALE WEATHER PATTERNS BY EARLY DECEMBER.
 A WEAK BUT PROGRESSIVE MJO IS NOW OUT IN THE WESTERN PACIFIC AND IS
 EXPECTED TO MAINTAIN SOME STRENGTH AND CONTINUE WEST OVER THE NEXT
 TEN DAYS.  IN ADDITION TROPICAL STORM NIDA IS EXPECTED TO BECOME A
 SUPER TYPHOON AND TURN NORTH OUT NEAR 135 E AND POSSIBLY GET
 ENTRAINED INTO THE WESTERLIES CLOSE TO DEC 1.  THE MODELS HAVE BEEN
 HINTING AT A POSSIBLE BREAK THROUGH JET UNDER WHAT WILL BECOME A
 HIGH AMPLITUDE RIDGE OVER THE WEST COAST THE NEXT 5 TO 7 DAYS.  THE
 GFS HAS BEEN MORE ROBUST WITH THIS BREAKTHROUGH THAN HAS THE
 ECMWF. AS WE HAVE A MODERATE EL NINO PATTERN EXISTING THE FORECAST
 ISSUE IS WHEN AND IF THIS EL NINO WILL MANIFEST ITSELF WITH A MORE
 SOUTHERLY JET INTO CA AND INCREASING WET WEATHER.  EARLY DECEMBER
 IS ABOUT THE TIME WHEN A MODERATE EL NINO MIGHT BEGIN TO EXERT
 ENOUGH FORCING ON THE EAST ASIAN JET TO ALLOW IT TO EXTEND TO THE
 WEST COAST AT THE LATITUDE OF CENTRAL CALIFORNIA.  THE KICKER MAY
 JUST BE WHAT HAPPENS TO TYPHOON NIDA AND IF THE MJO CAN SUSTAIN
 ITSELF LONG ENOUGH TO EXTEND THE EAST ASIAN JET UNDER THE HIGH
 AMPLITUDE RIDGE.  IF THIS WERE TO HAPPEN IT APPEARS THAT THE
 EARLIEST THIS WOULD BE THE SECOND WEEK OF DECEMBER.  WITH THE
 MODELS AND THERE ENSEMBLES CONTINUING TO PUSH THIS BACK CONFIDENCE
 IS NOT HIGH.  BUT THE MANY FACTORS NOTED ABOVE ARE ALL MAJOR PLAYERS
 THAT WOULD LEAD TO A CHANGE TO WET WEATHER BY LATE WEEK TWO OR
 EARLY WEEK THREE.
 
 
 
 &&
 
 .AVIATION...AS OF 4 AM PST TUESDAY...DRY AIRMASS REMAINS IN PLACE
 WITH MOSTLY CLEAR SKIES.  ONLY RESTRICTION IS PATCHY FOG IN THE N
 BAY NEAR KSTS.  THIS FOG WILL LINGER THROUGH MID MORNING.
 
 ALL TERMINALS(EXCEPT KSTS)...VFR CONDITIONS EXPECTED WITH LIGHT
 WINDS.
 
 &&
 
 
 .MTR WATCHES/WARNINGS/ADVISORIES...
     .TDY...NONE.
 
 
 

 
 PUBLIC FORECAST: REYNOLDS
 AVIATION/MARINE: MEHLE
 
 NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO
 
 

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