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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
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