AREA FORECAST DISCUSSION

 
 FXUS66 KMTR 241634
 AFDMTR
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
 834 AM PST TUE NOV 24 2009
 
 .DISCUSSION...AS OF 8:00 AM PST TUESDAY...FORECAST FOCUS IN ON DRY
 TRAVEL WEATHER TODAY THROUGH THANKSGIVING DAY ACROSS THE BAY AREA
 AND MOST OF CALIFORNIA. SOME LIGHT RAIN POSSIBLE THURSDAY NIGHT
 MAINLY IN THE NORTH BAY.
 
 SHORT TERM...SKIES ARE MOSTLY CLEAR ACROSS THE CWA THIS MORNING
 WITH A FEW HIGH CLOUDS OVER THE NORTH BAY. EXPECT ANOTHER NICE LATE
 NOVEMBER DAY ACROSS NORTHERN CALIFORNIA WITH TEMPS WARMING 65 TO 70
 THIS AFTERNOON FOR MANY SITES. CURRENT PRESSURE GRADIENTS SHOW 12 MB
 OFFSHORE FROM WMC TO SFO WHICH WILL ALLOW FOR SOME ADIABATIC
 WARMING TODAY. OAKLAND NORTH RAWS SHOWS NORTHEAST WINDS GUSTING TO
 39 MPH IN THE EAST BAY HILLS.  WINDS IN THE HILLS WILL EASE THIS
 AFTERNOON THEN RAMP BACK UP AGAIN TONIGHT WITH LITTLE CHANGE IN THE
 OVERALL PATTERN. HOWEVER WINDS TO REMAIN BELOW ADVISORY CRITERIA
 FOR THE HILLS.
 
 NOT MUCH CHANGE INTO WEDS WITH STRONG HIGH PRESSURE OVER CALIFORNIA
 AND MUCH OF THE WEST COAST. DONT REALLY SEE ANY TRAVEL PROBLEMS FOR
 THOSE DRIVING IN THE CENTRAL VALLEY (ONLY PATCHY FOG) AND NO SNOW
 EXPECTED IN THE SIERRA. AIRPORT TERMINALS LOOK GOOD TOO WITH NO LOW
 CIGS OUR FOG EXPECTED THE NEXT 24-36 HOURS.
 
 PREVIOUS DISCUSSION BELOW FROM 3 AM TUESDAY....
 
 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 8:30 AM PST TUESDAY...THE DRY AIRMASS WILL
 CONTINUE...PRODUCING MOSTLY CLEAR SKIES.  PATCHY FOG IN THE
 VALLEYS POSSIBLE FOR TONIGHT.
 
 ALL TERMINALS(EXCEPT KSTS)...VFR CONDITIONS EXPECTED WITH LIGHT
 WINDS.
 
 &&
 
 
 .MTR WATCHES/WARNINGS/ADVISORIES...
     .TDY...NONE.
 
 
 

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