AREA FORECAST DISCUSSION

 
 FXUS66 KMTR 250107
 AFDMTR
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
 505 PM PST TUE NOV 24 2009
 
 .DISCUSSION...AS OF 1:30 PM PST TUESDAY...SHORT TERM WEATHER CONCERNS
 ARE MINIMAL WITH ONLY MEDIUM TERM ISSUE ON RAIN CHANCES THANKSGIVING
 NIGHT...MAINLY FOR THE NORTH BAY.
 
 IN THE SHORT TERM...SKIES ARE SUNNY THIS AFTERNOON WITH TEMPS
 RUNNING 5 TO 10 DEGREES WARMER THAN YESTERDAY AT THIS TIME WITH HIGH
 PRESSURE BUILDING AND OFFSHORE SURFACE PRESSURE GRADIENTS.
 CURRENTLY ITS 68 IN DOWNTOWN OAKLAND WITH RECORD HIGH FOR TODAY ONLY
 71 SO TEMPS ARE RUNNING ABOVE NORMAL. OFFSHORE GRADIENTS ARE STILL
 STRONG WITH 10 MB FROM THE GREAT BASIN TO THE COAST WITH 1 MB FROM
 SAC TO SFO. THESE OFFSHORE GRADIENTS WILL KEEP SOME LOCALLY GUSTY
 NORTHEAST WINDS GOING TONIGHT ACROSS THE EAST BAY HILLS BUT WINDS
 ARE FORECAST TO STAY BELOW ADVISORY CRITERIA IN THE HILLS. LAST NIGHT
 THE WINDS IN THE HILLS KEPT TEMPS IN THE 50S TO NEAR 60 AND WOULD
 EXPECT SIMILAR TONIGHT WITH CHILLY READINGS IN THE VALLEYS BUT MILD
 IN THE HILLS WITH 850 MB TEMPS AROUND 10 CELSIUS.
 
 NOT MUCH CHANGE INTO WEDS WITH HIGH PRESSURE ALOFT STAYING OVERHEAD
 ALTHOUGH SURFACE GRADIENTS RELAX. EITHER WAY THIS ALL POINTS TO
 GOOD TRAVEL WEATHER ACROSS THE STATE WITH MAINLY CLEAR SKIES...NO
 PRECIP AND MINIMAL FOG EXPECTED IN THE GREAT VALLEY...BOTH FOR CAR
 TRAVEL AND AIR TRAVEL.
 
 THANKSGIVING DAY STARTS OUT SUNNY ACROSS THE SF BAY AREA BUT THEN A
 TROUGH OVER THE OCEAN APPROACHES THE NORTH COAST BY LATE IN THE
 DAY. NO RAIN IS FORECAST FOR THE DAYLIGHT HOURS OF THANKSGIVING. BY
 THURSDAY NIGHT LIGHT RAIN WILL BE POSSIBLE IN THE NORTH BAY WITH
 SLIGHT CHANCES FOR THE BAY AREA PROPER. HOWEVER ANY FRONT THAT
 PASSES THROUGH ON THURSDAY NIGHT WILL BE FALLING APART AS IT PASSES
 OVER OUR LATITUDES. ANY PRECIP TOTALS WOULD AVERAGE 0.10 FOR THE
 NORTH BAY WITH ONLY TRACE TO A FEW HUNDREDTHS FOR THE BAY AREA.
 
 ANY PRECIP CHANCES END BY SUNRISE FRIDAY AS HIGH PRESSURE REBUILDS
 OVER THE REGION.  THE WEEKEND WEATHER LOOKS REAL NICE WITH MORE
 OFFSHORE WIND FLOW AND TEMPS RUNNING SEVERAL DEGREES ABOVE NORMAL.
 ONCE AGAIN ANY WINDS IN THE HILLS SHOULD REMAIN BELOW ADVISORY
 CRITERIA WITH A FAIRLY TYPICAL LATE FALL OFFSHORE SYNOPTIC SET-UP.
 
 12Z GFS SHOWED SOME POSSIBLE UNDER-CUTTING OF PRECIP BY ABOUT NEXT
 WEDS BUT GFS ENSEMBLE MEMBERS AND 12Z ECMWF WERE NOT SUPPORTIVE OF
 A PATTERN CHANGE. IN LOOKING AT THE 12Z GFS ENSEMBLE SOLUTIONS THE
 GENERAL CONSENSUS AT THIS TIME INDICATES WEST COAST RIDGING WITH A
 COLD TROUGH OVER THE MIDDLE OF THE CONUS.
 
 PREVIOUS LONG RANGE DISCUSSION BELOW FROM MID-SHIFT 3 AM TUESDAY....
 
 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 5:05 PM PST TUESDAY...CLEAR SKIES WILL PERSIST
 THROUGH WEDNESDAY UNDER THE INFLUENCE OF HIGH PRESSURE. PATCHY FOG
 IS POSSIBLE ONCE AGAIN IN THE VALLEYS TONIGHT.
 
 ALL TERMINALS(EXCEPT KSTS)...VFR CONDITIONS EXPECTED THROUGH
 WEDNESDAY WITH LIGHT WINDS.
 
 &&
 
 
 .MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...NONE.
 
 
 

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