Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000 FXUS66 KMTR 020344 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 844 PM PDT TUE SEP 1 2015 .SYNOPSIS...ASIDE FROM THE POSSIBILITY OF COASTAL DRIZZLE TONIGHT INTO WEDNESDAY MORNING...DRY WEATHER CONDITIONS WILL PERSIST THROUGH THE UPCOMING WEEKEND. TEMPERATURES WILL COOL THROUGH LATE WEEK AS AN UPPER LEVEL TROUGH DIGS SOUTHWARD INTO THE PACIFIC NORTHWEST. WARMER AND DRIER CONDITIONS RETURN FOR THE UPCOMING WEEKEND. && .DISCUSSION...AS OF 8:44 PM PDT TUESDAY...ANOTHER MILD EVENING ANTICIPATED TONIGHT WITH TEMPERATURES CURRENTLY RUNNING IN THE LOWER TO MID 60S ALONG THE COAST TO MID 70S INLAND. SATELLITE IMAGERY SHOWS A STRIP OF STRATUS ALONG THE COAST EXTENDING SOUTH FROM HALF MOON BAY. PATCHY STRATUS IS ANTICIPATED ONCE AGAIN TONIGHT WITH LOCALIZED DRIZZLE IN RESPONSE TO AN APPROACHING UPPER LEVEL DISTURBANCE THAT IS EXPECTED TO FURTHER DEEPEN THE MARINE LAYER. COOLER TEMPERATURES ARE IN STORE WEDNESDAY AS THE WEAK UPPER LEVEL SHORT WAVE SWINGS ACROSS THE REGION. THE COOLING TREND WILL CONTINUE THROUGH THE LATER HALF OF THE WEEK AS THE LONGWAVE TROUGH DIGS SOUTH OVER THE PACIFIC NORTHWEST INTO NORTHERN CALIFORNIA INTRODUCING A COOLER AIRMASS ACROSS THE NORTHERN HALF OF THE STATE. 850 MB TEMP AND 500 MB HEIGHTS WILL PLUMMET THROUGH THE END OF THE WEEK REACHING A LOW OF 8.5 C AND 269 DAM FRIDAY NIGHT. THIS WILL TRANSLATE INTO HIGHS IN THE 60S ALONG THE COAST AND 70S INLAND WITH LOWS IN THE 50S OVER LOW LYING AREAS AND 40S OVER HIGHER ELEVATIONS. THIS SYSTEM IS FORECAST TO KICK OUT TO THE NORTHEAST ON SATURDAY AND WILL BE REPLACED BY AN AREA OF HIGH PRESSURE BUILDING IN FROM THE WEST. THIS WILL KICK START A WARMING TREND THAT IS FITTING OF THE LABOR DAY WEEKEND. FURTHER WARMING IS ANTICIPATED SUNDAY AND MONDAY AS A THERMAL TROUGH SETS UP OVER THE STATE THEN SHIFTS WEST OVER THE COAST. WARM AND DRY CONDITIONS WILL PERSIST THROUGH EARLY NEXT WEEK WITH NO RAIN IN THE FORECAST THROUGH NEXT WEEK. FORECAST APPEARS ON TRACK...NO UPDATE NEED AT THIS TIME. && .AVIATION...AS OF 5:25 PM PDT TUESDAY...PATCHY COASTAL STRATUS SEEN FROM SOUTHERN MARIN COUNTY TO NORTHERN MONTEREY COUNTY OTHERWISE VFR. THE FORECAST AREA IS ON THE BOUNDARY BETWEEN VERY WEAK UPPER LEVEL SW AND NW WINDS CAUSING A NARROW BUT LONG BAND OF CIRRUS SEEN ON THE VISIBLE IMAGERY. A FAIRLY DECENT SMX-SFO PRESSURE GRADIENT IS PERSISTING SINCE LATE LAST EVENING...PRESENTLY 2 MB. NW WINDS OVER THE INNER COASTAL WATERS ARE TENDING TO WEAKEN BECAUSE OF THIS SOUTH-NORTH DIRECTED GRADIENT. ONSHORE WINDS WILL PERSIST THIS EVENING HOWEVER...DRIVEN BY A SLOWLY INCREASING SFO-SAC GRADIENT PRESENTLY 2.4 MB. STRATUS AND FOG ARE EXPECTED TO INCREASE TONIGHT WITH INCREASING INLAND INTRUSION...BUT MAINLY LATE TONIGHT INTO WEDNESDAY MORNING. THE GFS MODEL IS CONSISTENT WITH FORECASTING A FAIRLY VIGOROUS LOW-LEVEL TROUGH OVER THE EPAC TO SLIDE SOUTHWARD OVER THE COASTAL WATERS TOMORROW. INCREASING BOUNDARY LAYER HUMIDITY OVERNIGHT INTO WEDNESDAY MORNING COUPLED WITH LOWER LEVEL COOLING WILL LIKELY ENHANCE STRATUS CLOUD COVER POSSIBLY CAUSING A FEW LOCALIZED POCKETS OF DRIZZLE. MESOSCALE MODEL PREDICTS 3-4 MB ACV-SFO GRADIENT WEDNESDAY INTO WEDNESDAY NIGHT BUT GIVEN BACK-DROP OF THE MID-WEEK WEATHER PATTERN WOULD NOT BE SURPRISED IF IT BECAME A BIT STRONGER. IF IT DOES W-NW WINDS WILL TEND TO BE A BIT GUSTIER THAN ADVERTISED AND SKIES WILL TEND TO CLEAR OUT FASTER FROM NORTH-SOUTH WED EVENING AND NIGHT. VICINITY OF KSFO...VFR. INCREASING MARINE LAYER DEPTH FORECAST DURING THE PERIOD. MVFR CIGS BEGINNING EARLY WED MORNING...BUT LESS CONFIDENT ABOUT HOW LONG CIGS WILL LAST AT KSFO WED. FEW-SCT014-015 FORECAST LATE MORNING THROUGH AFTERNOON. MODEL GUIDANCE INDICATES GUSTY WESTERLY WINDS WED AFTERNOON AND EVENING SUSTAINED AND GUSTS UP OVER 20 KNOTS. KSFO BRIDGE APPROACH...SIMILAR TO KSFO. MONTEREY BAY AREA TERMINALS...SW-W WIND FLOW INTO THE MONTEREY BAY WITH STRATUS CLOUDS GRADUALLY APPROACHING THE TERMINALS THIS EVENING. IFR CIGS FORECAST TO DEVELOP 03Z-06Z...IFR PREVAILING OVERNIGHT. MVFR CIGS LATE WED MORNING WITH PARTIAL CLEARING BY WED AFTERNOON. && .MARINE...AS OF 1:51 PM PDT TUESDAY...A WEAK SURFACE PRESSURE GRADIENT WILL MAINTAIN GENERALLY LIGHT WINDS OVER A GOOD PORTION OF THE COASTAL WATERS THROUGH WEDNESDAY AFTERNOON. MODERATE WINDS ARE HOWEVER EXPECTED TO PERSIST OVER THE NORTHERN OUTER COASTAL WATERS THROUGH TONIGHT. THE SURFACE PRESSURE GRADIENT IS EXPECTED TO INCREASE FOR THE SECOND HALF OF THE WEEK...RESULTING IN STRENGTHENING WINDS. && .MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...SCA...PT ARENA TO PIGEON PT 10-60 NM UNTIL 2 AM SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 2 AM SCA...SF BAY UNTIL 8 PM && $$ PUBLIC FORECAST: CW AVIATION: CANEPA MARINE: LARRY VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO FOLLOW US ON FACEBOOK AND TWITTER AT: WWW.FACEBOOK.COM/NWSBAYAREA WWW.TWITTER.COM/NWSBAYAREA

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