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

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000 FXUS66 KMTR 180341 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 841 PM PDT FRI APR 17 2015 .SYNOPSIS...HIGH PRESSURE THIS WEEKEND WILL BRING SEASONABLE TEMPERATURES WITH TRANQUIL CONDITIONS. BY MONDAY SOME INSTABILITY WILL DEVELOP OVER THE REGION...PRODUCING CUMULUS CLOUDS AND A SLIGHT CHANCE OF AN ISOLATED SHOWER OR THUNDERSTORM ACROSS SOME OF THE REMOTE INTERIOR HILLS. BY TUESDAY AND WEDNESDAY AN UPPER LOW WILL APPROACH...RESULTING IN A COOLING TREND ALONG WITH A SLIGHT CHANCE OF SHOWERS...MAINLY OVER THE HILLS. && .DISCUSSION...AS OF 8:40 PM PDT FRIDAY...A SHALLOW MARINE LAYER DEVELOPED TODAY...RESULTING IN UP TO TEN DEGREES OF COOLING NEAR THE IMMEDIATE COAST...MAINLY FROM SAN MATEO COUNTY NORTHWARD. BUT MOST AREAS AWAY FROM THE COAST REMAINED ISOLATED FROM THE COOLING EFFECTS OF THE SHALLOW MARINE LAYER AND LIGHT ONSHORE FLOW AND ENDED UP BEING AS WARM AS YESTERDAY...OR EVEN A BIT WARMER. A RECORD HIGH OF 86 OCCURRED IN SANTA CRUZ TODAY AND SALINAS TIED THEIR RECORD HIGH FOR THE DAY WITH AN 81. A WEAK SHORTWAVE TROUGH IS CURRENTLY MOVING INLAND ACROSS THE PAC NW. THIS WEAK UPPER LEVEL DISTURBANCE IS FORECAST TO DROP SOUTH INTO NORTHERN CA ON SATURDAY AND THEN FORM A WEAK CUTOFF LOW OFF THE NORTHERN CA COAST BY LATE SUNDAY. THIS SYSTEM IS EXPECTED TO BE TOO WEAK AND DRY TO GENERATE ANY PRECIP OVER OUR AREA THROUGH THE WEEKEND...BUT IT WILL LIKELY RESULT IN AN INCREASE IN THE DEPTH OF THE MARINE LAYER AND THUS AT LEAST SLIGHT COOLING OVER THE NEXT TWO DAYS. ONSHORE FLOW IS FORECAST TO REMAIN WEAK THROUGH THE WEEKEND AND SO INLAND AREAS WILL PROBABLY SEE ONLY MODEST COOLING. THE UPSHOT IS THAT COASTAL AREAS CAN EXPECT AREAS OF LOW CLOUDS AND FOG THIS WEEKEND...BUT INLAND AREAS SHOULD REMAIN MOSTLY CLEAR AND WARM. BY MONDAY ONSHORE FLOW IS EXPECTED TO INCREASE WHICH WILL BE THE START OF A REGION-WIDE COOLING TREND. IN ADDITION...MOISTURE IS FORECAST TO INCREASE SOMEWHAT ACROSS THE SOUTHERN PART OF OUR FORECAST AREA ON MONDAY AND THERE MAY BE JUST ENOUGH INSTABILITY OVER THE HIGHER HILLS BY THAT AFTERNOON TO GENERATE ISOLATED SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF SOUTHERN SAN BENITO COUNTY. THE COOLING TREND IS EXPECTED TO RAMP UP ON TUESDAY AS AN UPPER TROUGH APPROACHES FROM THE NW. THAT TROUGH IS THEN FORECAST TO DIG SOUTH ALONG THE CA COAST ON TUESDAY NIGHT AND WEDNESDAY...FORMING AN UPPER LOW NEAR THE CENTRAL CA COAST BY LATE WEDNESDAY. SHOWER CHANCES WILL SPREAD FROM NORTH TO SOUTH ACROSS OUR REGION FROM TUESDAY INTO WEDNESDAY...BUT THE MEDIUM RANGE MODELS AGREE THAT THE BULK OF THE PRECIPITATION WITH THIS MIDWEEK SYSTEM WILL FALL OVER THE HIGHER MOUNTAINS OF CA (E.G., SIERRA NEVADA). THE PATTERN IS FORECAST TO REMAIN UNSETTLED INTO LATE NEXT WEEK...BUT THE LIKELIHOOD OF RAINFALL OF ANY SIGNIFICANCE IS DIFFICULT TO PREDICT AT THIS POINT GIVEN MODEL DIFFERENCES. THE 12Z ECMWF OFFERS THE BEST HOPE OF WIDESPREAD RAINFALL...SHOWING A POTENT AND RELATIVELY WET LITTLE SYSTEM SWEEPING ACROSS CENTRAL CA FROM LATE NEXT FRIDAY THROUGH SATURDAY MORNING. && .AVIATION...AS OF 4:49 PM PDT FRIDAY...THE CURRENT VISIBLE SATELLITE IMAGE IS SHOWING STRATUS MOVING IN ALONG THE CENTRAL CALIFORNIA COAST THIS EVENING WITH CLEAR SKIES OVER LAND. THE FORT ORD PROFILER IS SHOWING A SHALLOW MARINE LAYER DEVELOPING. WITH ONSHORE FLOW INCREASING THE SHALLOW MARINE LAYER MAY BE ADVECTED INTO THE SAN FRANCISCO BAY AREA RESULTING IN LOW CIGS LATER THIS EVENING. THE WRF HIGH RES FORECAST MODEL DEVELOPS AN EDDY IN MONTEREY BAY WHICH MAY KEEP STRATUS OUT OF THE MONTEREY BAY AREA TERMINALS OVERNIGHT. VICINITY OF KSFO...VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH AROUND 1100Z AT WHICH POINT BKN-OVC008 WILL BE POSSIBLE. FIRST GUESS AT THE MORNING BURN OFF IS 1600 TO 1700Z. CONFIDENCE IS MODERATE. SFO BRIDGE APPROACH...SIMILAR TO KSFO. MONTEREY BAY AREA TERMINALS...VFR IS EXPECTED TO PREVAIL THROUGH THE NEXT 24 HOURS. HOWEVER...A PERIOD OF LOW CIGS BKN-OVC008 WILL BE POSSIBLE AFTER MIDNIGHT. CONFIDENCE IS MODERATE. && ...BEACH HAZARD STATEMENT IN EFFECT THROUGH FRIDAY EVENING... .BEACHES...AS OF 10:15 AM PDT FRIDAY...LONG PERIOD SWELLS OF 17-19 SECONDS WILL CONTINUE THROUGH THIS EVENING. THE LONG PERIOD WAVES WILL COINCIDE DURING A PERIOD OF LIGHT OFFSHORE WINDS PROMOTING GLASSY WAVE CONDITIONS SUPPORTIVE OF LARGE BREAKING WAVES. THESE STRONG WAVES WILL PROMOTE HAZARDOUS BEACH CONDITIONS INCLUDING STRONG RIP CURRENTS...LARGE SURF AND SNEAKER WAVES. VISITORS/DIVERS/SURFERS HEADING TO THE BEACH SHOULD REMAIN ALERT FOR RAPIDLY CHANGING SEA CONDITIONS. FISHERMEN SHOULD AVOID FISHING FROM ROCKS AND JETTIES AND BEACH VISITORS SHOULD REFRAIN FROM CLIMBING ON ROCKS OR VISITING STEEP BEACHES. NEVER TURN YOUR BACK TO THE OCEAN WHEN VISITING THE BEACH. IF YOU SEE SOMEONE BEING WASHED INTO THE OCEAN BY A WAVE DO NOT ATTEMPT TO RESCUE THEM ON YOUR OWN...YOU COULD BECOME A VICTIM YOURSELF. INSTEAD CALL 911 IMMEDIATELY FOR ASSISTANCE AND KEEP A CLOSE EYE ON THE VICTIM UNTIL HELP ARRIVES. && .CLIMATE...RECORD HIGH TEMPERATURES FOR FRIDAY (4/17) ALONG WITH THE MOST RECENT DATE IT OCCURRED. SF BAY AREA .LOCATION.................4/17 KENTFIELD...............89/1999 SAN RAFAEL..............88/1954 NAPA....................88/1954 SAN FRANCISCO...........79/1954 SFO AIRPORT.............82/1954 OAKLAND (DOWNTOWN)......78/1977 OAKLAND AIRPORT.........87/1954 RICHMOND................86/1954 LIVERMORE...............90/1966 MOFFETT FIELD...........83/1954 SAN JOSE................92/1999 GILROY..................92/1999 MONTEREY BAY AREA .LOCATION.................4/17 MONTEREY................80/1952 SANTA CRUZ..............84/1938 SALINAS.................81/1999 SALINAS AIRPORT.........87/1952 KING CITY...............98/1954 && .MARINE...AS OF 01:01 PM PDT FRIDAY...HIGH PRESSURE OFF THE PACIFIC NORTHWEST COAST WILL HELP TO MAINTAIN NORTHERLY FLOW ALONG THE CENTRAL COAST. NORTHWEST WINDS WILL INCREASE NORTH OF POINT REYES LATER TODAY...ESPECIALLY OVER THE OUTER WATERS. A LONG PERIOD WILL CONTINUE TO IMPACT THE COASTAL WATERS AS WELL. && .MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...SCA...PT ARENA TO PT REYES 10-60 NM SCA...ROUGH BAR ADVISORY FOR SF BAR UNTIL 6 AM SCA...SF BAY NORTH OF THE BAY BRIDGE UNTIL 9 PM && $$ PUBLIC FORECAST: DYKEMA AVIATION: LARRY MARINE: MM CLIMATE: HENDERSON/BELL VISIT US AT WEATHER.GOV/SANFRANCISCO FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSBAYAREA WWW.TWITTER.COM/NWSBAYAREA WWW.YOUTUBE.COM/NWSBAYAREA

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