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AREA FORECAST DISCUSSION

 
 FXUS66 KMTR 251750
 AFDMTR
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
 950 AM PST WED NOV 25 2009
 
 .DISCUSSION...AS OF 9:25 AM WEDNESDAY...SLIGHT CHANCE FOR PRECIP
 LATE THURSDAY AND EARLY FRIDAY FOLLOWED BY SEASONABLE WEATHER. HIGH
 SURF POTENTIAL FOR FRIDAY AFTERNOON.
 
 MILD OFFSHORE WIND FLOW OVER THE FORECAST AREA OVERNIGHT WITH WIDE
 VARIATION IN MINIMUM TEMPERATURES RELATIVE TO ELEVATION. LOWER
 COASTAL VALLEYS AND POINTS SUCH AS SANTA ROSA WITH WIND SHELTERING
 DROPPED INTO THE 30S WHILE UPPER ELEVATIONS SUCH AS HAWKEYE
 REMAINED WARM OVERNIGHT WITH A LOW OF 63F. HOWEVER...MOST WARMER
 LOCATIONS AROUND THE COASTAL AREA WERE AROUND 50F. OVER THE LAST 24
 HOURS...CHANGES VARIED +/-2F MOSTLY ALTHOUGH S.F. AND OAK REFLECTED
 THE MILD OFFSHORE CONDITIONS WITH INCREASES OF 6-7F. PATCHY DENSE
 VALLEY FOG REPORTED AROUND THE SANTA ROSA AREA AND SOME AREAS
 AROUND THE DELTA. THE RIDGE ALOFT CONTINUES OVER THE WEST COAST
 TODAY. WITH HIGH PRESSURE CENTERED OVER THE GREAT BASIN AND THE
 THERMAL TROF IMMEDIATELY ALONG THE CENTRAL COAST...THE 13MB WMC-SFO
 PRESSURE GRADIENT WILL SUPPORT NE WINDS 10-20MPH OVER HIGHER
 ELEVATIONS RESULTING IN TEMPERATURES AGAIN GENERALLY PUSHING ABOVE
 SEASONAL NORMALS AND GENERALLY DRY CONDITIONS.
 
 BASED ON PREVIOUS FORECAST...CURRENT LONGWAVE PATTERN HAS A RIDGE OF
 HIGH PRESSURE OVERHEAD AND OVER MUCH OF THE WEST COAST. FARTHER
 UPSTREAM A LOW PRESSURE SYSTEM AND ASSOCIATED COLD FRONT CONTINUES TO
 SWING THROUGH THE GULF OF AK AND A SECOND DEEPENING SHORTWAVE TROUGH
 IS NEAR 150W.
 
 SHORT TERM...THANKSGIVING-FRIDAY...
 THE RIDGE ALOFT WILL WEAKEN AND SLIDE TOWARD THE SOUTHEAST BY EARLY
 THURSDAY. AS THIS HAPPENS...A SECOND UPSTREAM FEATURE WILL DEEPEN
 AND MOVE TOWARD THE COAST THURSDAY. MODELS ARE IN DECENT AGREEMENT
 WITH THE TIMING OF THIS FEATURE. AS MENTIONED IN PREVIOUS DISCUSSIONS
 ...THANKSGIVING DAY STILL LOOKS TO START MOSTLY SUNNY BUT AS THE
 SHORTWAVE TROUGH AND ASSOCIATED FRONT MOVE CLOSER THROUGH THE DAY
 CLOUDS WILL STEADILY INCREASE. ALL MODEL GUIDANCE KEEPS ANY PRECIP
 WELL OFFSHORE THROUGH 4 PM ON THANKSGIVING.  AFTER 4 PM THE
 LIKELIHOOD FOR DEVELOPING LIGHT SHOWERS WILL INCREASE. MODEL GUIDANCE
 HAS BEEN PRETTY PERSISTENT WITH KEEPING THE BULK OF THE PRECIP SAN
 FRANCISCO BAY NORTHWARD. THE 00Z AND EARLY 12Z MODELS ARE NO
 DIFFERENT AND NO CHANGE IN FORECAST PACKAGE THIS MORNING. EVEN WITH
 THE ADVERTISED RAINFALL THURSDAY NIGHT INTO EARLY FRIDAY AMOUNTS WILL
 BE LIGHT...GENERALLY A FEW HUNDREDTHS TO A TENTH OR TWO AT THE MOST.
 WILL CONTINUE TO KEEP MUCH OF THE SOUTHERN FORECAST AREA DRY WITH
 ONLY CLOUDS MENTIONED.
 
 THE COLD FRONT WILL EXIT THE AREA ON FRIDAY WITH A CLEARING TO
 FOLLOW. A DROP IN TEMPERATURE IS EXPECTED ON FRIDAY WITH POST-
 FRONTAL COLD AIR ADVECTION AS 850 MB TEMPS DROP A FEW DEGREES AND
 COOL NORTHWEST FLOW DEVELOPS AT THE SFC.
 
 FRIDAY CONCERN IS THE ARRIVAL OF A LARGE WAVE TRAIN SPREADING DOWN
 THE COAST FRIDAY. HAZARDOUS WEATHER OUTLOOK HAS BEEN ISSUED TO
 REFLECT THREAT FOR HOLIDAY VISITORS TO THE CENTRAL COAST FROM THIS
 LARGE AND HIGH ENERGY SWELL. ANY FORMAL HIGH SURF ADVISORY WILL BE
 ISSUED EARLY THANKSGIVING DAY SHOULD MODELS MAINTAIN CONSISTENCY.
 
 LONG TERM...SATURDAY-TUESDAY...
 NO CHANGE MADE TO THE LONG TERM FORECAST.  HIGH PRESSURE IS
 FORECAST TO BUILD BEHIND THE DEPARTING COLD FRONT WITH A SLIGHT
 WARMING TREND. SOME INCONSISTENCY BETWEEN ECMWF AND GFS SOLUTIONS IN
 THAT THE ECMWF BUILDS A VERY HIGH AMPLITUDE RIDGE BY WEDNESDAY THAT
 EXTENDS WELL NORTHWARD ALONG THE BRITISH COLUMBIA COAST WHILE THE
 GFS MAINTAINS SOLUTIONS INDICATING THREAT OF WEAK ZONAL FLOW
 UNDERCUTTING THE RIDGE SAME TIME PERIOD. WATCHING FOR VERY REMOTE
 POSSIBILITY OF VERY STRONG TROPICAL CYCLONE NIDA MOISTURE ABLE TO
 ENTRAIN INTO ANY ZONAL FLOW BREAK-THROUGH. LACK OF CONSISTENCY DOES
 NOT GIVE ANY CONFIDENCE TO THIS SOLUTION AT THIS POINT IN TIME.
 PREVIOUSLY MENTION OF MADDEN-JULIAN OSCILLATION CONTRIBUTING TO THE
 CYCLONE MOISTURE AND POSSIBILITY OF BREAK-THROUGH ALSO BECOMING
 LESS LIKELY. STILL...WILL MAINTAIN WATCH FOR THIS VERY LOW
 PROBABILITY OF CONVERGING OF EVENTS FOR MIDWEEK TIME PERIOD. AT THIS
 POINT...DRY WEATHER WITH TEMPS AT OR EVEN SLIGHTLY ABOVE NORMAL
 BEST FORECAST.
 
 &&
 
 .AVIATION...AS OF 9:45 AM PST WEDNESDAY...CLEAR SKIES AND LIGHT
 WINDS WILL CONTINUE TO PREVAIL ACROSS THE AREA TODAY AND TONIGHT...
 AS HIGH PRESSURE OVER THE GREAT BASIN MAINTAINS A DRY AIR MASS AND A
 WEAK OFFSHORE ORIENTED PRESSURE GRADIENT. HOWEVER SOME PATCHY
 GROUND FOG CAN BE EXPECTED TO REDEVELOP AROUND KSTS LATE THIS
 EVENING.
 
 ALL TERMINALS(EXCEPT KSTS)...VFR CONDITIONS EXPECTED THROUGH
 WEDNESDAY WITH LIGHT WINDS.
 
 &&
 
 
 .MTR WATCHES/WARNINGS/ADVISORIES...
     .TDY...NONE.
 
 
 

 
 PUBLIC FORECAST: MM/GUDGEL
 AVIATION/MARINE: BLIER
 
 NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO
 
 

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