Since July 1, we have had 0.03 " of rain. Average seasonal rainfall for July 29th is 0.06". We are now at 50% of our normal rainfall for this date.

TODAY: PATCHY LOW CLOUDS AND FOG IN THE MORNING THEN SUNNY. HIGHS IN THE 70S TO LOWER 80S. SOUTHWEST WINDS 5 TO 10 MPH.

TONIGHT: CLEAR IN THE EVENING THEN PARTLY CLOUDY WITH PATCHY FOG. LOWS IN THE LOWER 50S. WEST WINDS 5 TO 15 MPH.

FRIDAY: PARTLY CLOUDY WITH PATCHY FOG IN THE MORNING THEN SUNNY. HIGHS IN THE 70S TO LOWER 80S. SOUTHWEST WINDS 5 TO 10 MPH.

FRIDAY NIGHT: CLEAR IN THE EVENING THEN PARTLY CLOUDY WITH PATCHY FOG. LOWS IN THE LOWER 50S. WEST WINDS 5 TO 15 MPH.

SATURDAY: PARTLY CLOUDY WITH PATCHY FOG IN THE MORNING THEN SUNNY. HIGHS IN THE MID 70S TO UPPER 80S. SOUTHWEST WINDS 5 TO 10 MPH.

SATURDAY NIGHT: CLEAR IN THE EVENING THEN PARTLY CLOUDY WITH PATCHY FOG. LOWS IN THE LOWER 50S.

SUNDAY THROUGH WEDNESDAY: PARTLY CLOUDY WITH PATCHY FOG. HIGHS IN THE 70S TO MID 80S. LOWS IN THE LOWER 50S. && TEMPERATURE / PRECIPITATION SANTA ROSA 73 51 76 / 0 0 0 SAN RAFAEL 75 53 73 / 0 0 0 NAPA 76 50 76 / 0 0 0

AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA 450 AM PDT THU JUL 29 2010

UPDATED AVIATION FORECAST

DISCUSSION: AS OF 3:55 AM PDT THURSDAY...LOW CLOUDS ARE AGAIN EXTENDING WELL INLAND EARLY THIS MORNING...GENERALLY SIMILAR TO 24 HR AGO EXCEPT FOR BEING LESS EXTENSIVE OVER THE COAST AND HILLS FROM ABOUT PIGEON PT SOUTHWARD. THIS PRIMARILY REFLECTS THE SHIFT IN SURFACE FLOW ORIENTATION THAT`S OCCURRED...FROM SOUTHWEST TO NORTHWEST. LATEST PROFILER AND SODAR DATA SHOW A MARINE LAYER DEPTH OF ABOUT 1700 FT AT BODEGA BAY...AND 2000 FT AT SAN CARLOS AIRPORT AND FT ORD...AND THUS INDICATE AROUND 800-1000 FT OF SHALLOWING SINCE THE SAME TIME YESTERDAY. THE PROFILERS ALSO INDICATE ABOUT 2C OF WARMING HAS OCCURRED ABOVE THE MARINE LAYER. ON THE OTHER HAND...THE ONSHORE PRESSURE GRADIENT BETWEEN SFO AND SAC HAS INCREASED SLIGHTLY...FROM 2.0 MB AT 10Z YESTERDAY TO 2.6 MB AT 10Z TODAY.

IN GENERAL...CONTINUE TO EXPECT BASICALLY PERSISTENT WEATHER CONDITIONS OVER THE NEXT 7 DAYS...AS LATEST LONG RANGE MODELS KEEP THE LONG WAVE UPPER LEVEL TROUGH AXIS PARKED ALONG THE WEST COAST. THIS WILL ACT TO GENERALLY MAINTAIN THE MARINE LAYER...ONSHORE FLOW...AND A SOMEWHAT COOLER THAN NORMAL AIR MASS ALOFT. THAT SAID... DO EXPECT SOME LESSER MAGNITUDE CHANGES AND DAY-TO-DAY VARIATIONS.

OVER THE NEXT COUPLE OF DAYS...MODELS ARE IN BASIC AGREEMENT THAT A BIT OF ADDITIONAL AIR MASS WARMING WILL OCCUR ALOFT...WHICH SHOULD BE REFLECTED IN AFTERNOON TEMPS INLAND GENERALLY INCREASING A FEW DEG PER DAY. NOT MUCH CHANGE IS EXPECTED AT THE COAST HOWEVER AS THE COOL ONSHORE FLOW...ALBEIT NOW OUT OF THE NORTHWEST...WILL CONTINUE.

THEN IN THE SATURDAY AFTERNOON TO SUNDAY TIME FRAME...THE NAM AND TO A LESSER DEGREE THE GFS AND ECMWF HINT AT ANOTHER WEAK SHORTWAVE ROTATING IN TOWARDS THE COAST...WHICH WOULD ACT TO ENHANCE THE MARINE LAYER AND INCREASE THE ONSHORE FLOW A BIT...AND THUS BRING SOME MODEST COOLING TO ALL BUT THE MOST SEABREEZE PROTECTED INLAND AREAS.

FURTHER INTO THE EXTENDED...AS NOTED ABOVE...THE LONG WAVE UPPER LEVEL TROUGH AXIS IS EXPECTED TO REMAIN IN THE VICINITY OF THE WEST COAST. LATEST MODEL OUTPUT DOES SUGGEST HOWEVER THAT IT WILL WEAKEN A BIT AND SHIFT A TAD EASTWARD DURING THE FIRST PART OF NEXT WEEK...WHICH WOULD RESULT IN LESS STRATUS AND A MODEST WARMING TREND FOR US.

&&

AVIATION: AS OF 4:50 AM PDT THURSDAY...WEAK LOW PRESSURE ALOFT IMMEDIATELY ALONG THE CENTRAL CALIFORNIA COAST CONTINUES TO ENHANCE THE MARINE LAYER ALONG THE COAST SLIGHTLY HIGHER THAN CLIMATE NORMAL. AND ALTHOUGH SURFACE FLOW ALONG THE COAST IS BEGINNING TO RESPOND TO BUILDING HIGH PRESSURE ALONG THE WEST COAST AND VEER TO THE NORTHWEST...ONSHORE SEA BREEZES PERSISTENTLY DEVELOP OVER AREA TERMINALS AFTER 20Z IN THE AFTERNOON HOURS. MVFR OVC CIG IN STRATUS WITH TOPS JUST OVER 2000 FT MSL AND SLIGHTLY LOWER THAN YESTERDAY. EXPECT STRATUS TO BURN BACK TO THE COAST BY 1830Z AROUND S.F.BAY AND AFTER 19Z ALONG THE CENTRAL COAST PROVIDING CAVU CONDITIONS. VFR/CAVU INLAND AREAS. MVFR CIG IN STRATUS RETURNING TO CENTRAL COAST BY 05Z AND S.F.BAY AFTER 07Z THIS EVENING.

VICINITY OF KSFO...MVFR CIG OVC011-013 IN STRATUS WITH LITTLE LOWER TOPS021 FROM YESTERDAY SO HAVE PLACED CLEARING 30-45 MINS EARLIER FOR KSFO THIS MORNING TO AROUND 18Z TIME PERIOD. CAVU AFTER 18Z WITH AFTERNOON WINDS AFTER 21Z 18G25KTS AS ONSHORE SURFACE PRESSURE GRADIENT SLIGHTLY HIGHER THAN YESTERDAY.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MRY BAY AREA TERMINALS...MVFR OVC CIG010-012 TOPS021. BECOMING CAVU AFTER 19Z FOR KMRY AND 18Z FOR KSNS. AFTERNOON WINDS AT KMRY AFTER 21Z WEST 11G16KTS AND KSNS 15G20KTS. STRATUS RETURNING WITH MVFR CIG OVC010 AROUND 05Z THIS EVENING.

&&

MTR WATCHES/WARNINGS/ADVISORIES... THIS AFTN AND EVE...SCA...SAN FRANCISCO BAY.

&&

PUBLIC FORECAST: BLIER AVIATION/MARINE: GUDGEL...PERSONAL NOTE: THIS IS MY LAST FORECAST SHIFT. I HAVE SEEN AND HELPED MOVE THE NWS FROM FACSIMILE CHARTS TO FLAT SCREEN MONITORS...AND TELETYPES TO TERA-BYTES OVER MY 36 YEARS OF SERVICE. I HAVE BEEN BLESSED TO SERVE IN THE ORIGINAL DECISION SUPPORT ROLES IN AIR POLLUTION...AG...FIRE WEATHER...AVIATION...AND MARINE PROGRAMS. THE SERVICE HAS ALWAYS BEEN ABOUT NWS CUSTOMERS AND THE ENJOYMENT OF THE FELLOWSHIP OF KINDRED SPIRITS WITHIN THE NWS TOWARD THAT END. IN GODS GRACE IN RETIREMENT I RETURN BACK TO THOSE FIRST LOVES OF AVIATION AND AG THAT BROUGHT ME TO METEOROLOGY AND WISH ONLY THE BEST FOR THOSE THAT CONTINUE TO SERVE THE NATION THROUGH THE FINEST OF GOVERNMENT AGENCIES...THE NWS.

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO