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

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000 FXUS66 KMTR 041636 AFDMTR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 936 AM PDT TUE AUG 4 2015 .SYNOPSIS...SUBTROPICAL MOISTURE MOVING IN FROM THE SOUTHWEST MAY RESULT IN ISOLATED SHOWERS AND THUNDERSTORMS THIS AFTERNOON...MAINLY OVER THE SAN FRANCISCO BAY AREA AND PARTICULARLY IN THE NORTH BAY. OTHERWISE...MILD TEMPERATURES ARE FORECAST TO CONTINUE THROUGH TUESDAY. A MODEST WARMING TREND IS THEN EXPECTED WEDNESDAY AND THURSDAY AS HIGH PRESSURE BUILDS ACROSS THE REGION. COOLER TEMPERATURES WITH ISOLATED SHOWERS AND THUNDERSTORMS MAY OCCUR FRIDAY. && .DISCUSSION...AS OF 09:30 AM PDT TUESDAY...A WEAK MID/UPPER LEVEL DISTURBANCE CONTINUES TO APPROACH THE SAN FRANCISCO BAY AREA THIS MORNING FROM THE SOUTHWEST. THIS FEATURE AIDED IN LESS WIDESPREAD COVERAGE OF STRATUS THIS MORNING...WITH ONLY PATCHY LOW CLOUDS REPORTED INLAND. WHILE MOISTURE ALOFT IS LIMITED WITH THIS SYSTEM...CANNOT RULE OUT ISOLATED SHOWERS AND THUNDERSTORMS THROUGH THE AFTERNOON. THE BEST CHANCES WILL GENERALLY BE ACROSS SAN MATEO AND ALAMEDA COUNTIES AND AREAS NORTHWARD THROUGH THE NORTH BAY. THE LATEST KMUX RADAR DATA DOES SHOW RETURNS OVER THE COASTAL WATERS AT THIS HOUR...YET MUCH OF THIS IS LIKELY ELEVATED AND NOT REACHING THE SURFACE. WILL CONTINUE TO MONITOR THIS THROUGH THE AFTERNOON AS THE DISTURBANCES SWEEPS ACROSS THE REGION. HAVE MADE A FEW ADJUSTMENTS TO THE FORECAST TO REFLECT THE CURRENT ANALYSIS AND LATEST MODEL GUIDANCE. && .PREV DISCUSSION...AS OF 3:30 AM PDT TUESDAY...SATELLITE IMAGE SHOWS STRATUS IS SLOWER TO MOVE ONSHORE THIS MORNING. THE STRATUS IS FINALLY FILLING IN OVER THE COASTAL WATERS AND IS STILL EXPECTED TO REACH THE SFO AND MRY BAY AREA AFTER SUNRISE. MID AND HIGH CLOUDS WILL INCREASE OVER THE SFO BAY AREA AND NORTH BAY AS AN UPPER LEVEL DISTURBANCE APPROACHES THE NORTHERN CALIFORNIA COAST. THIS DISTURBANCE WILL MOVE INLAND THIS AFTERNOON WITH MODELS INDICATING WEAK INSTABILITY OVER THE NORTH BAY AS THE SYSTEM MOVES INLAND WITH CAPE VALUES AROUND 200 J/KG. THE COMBINATION OF THE WEAK INSTABILITY AND THE MOISTURE WILL BRING A SLIGHT CHANCE OF SHOWERS OR THUNDERSTORMS FROM THE SFO BAY AREA NORTH THIS AFTERNOON. TEMPERATURES WILL BE ABOUT 3-5 DEGREES COOLER TODAY. CONVECTION THREAT WILL END TUESDAY EVENING AS THE SYSTEM MOVES NORTHEAST. DRIER SOUTHWEST FLOW ALOFT WILL BRING WARMER TEMPERATURES TO THE AREA WEDNESDAY AND THURSDAY. THE STRATUS SHOULD REMAIN INTACT AND CONTINUE TO BRING NIGHT AND MORNING LOW CLOUDS TO THE COASTAL AREAS. ANOTHER UPPER LEVEL LOW WILL APPROACH THE STATE ON FRIDAY. MEDIUM RANGE MODELS INDICATE THIS IS A SLIGHTLY STRONGER SYSTEM...WILL HAVE MORE INSTABILITY THROUGH UPWARD VERTICAL MOTION...AND WILL MOVE ACROSS OUR CWA. HAVE INTRODUCED A SLIGHT CHANCE OF CONVECTION FROM THE SFO BAY AREA NORTH FOR FRIDAY. TEMPERATURES WILL BE COOLER. DRY SOUTHWESTERLY FLOW RETURNS FOR NEXT WEEKEND. && .AVIATION...AS OF 4:58 AM PDT TUESDAY...FOR 12Z TAFS...HIGH CLOUDS CONTINUE TO MOVE ACROSS THE REGION THIS MORNING WITH LOW CLOUDS GRADUALLY FILLING IN ALONG THE COAST AND DEVELOPING LOCALLY INLAND. TEMPORARY CIGS ANTICIPATED THIS MORNING WITH AND EARLY CLEARING EXPECTED. WINDS WILL REMAIN LIGHT THROUGH MIDDAY. MODERATE CONFIDENCE. VICINITY OF KSFO...TEMPORARY MVFR CIGS EXPECTED TO FORM BETWEEN 12Z-16Z THIS MORNING. LIGHT WINDS AROUND 10 KT WILL INCREASE TO AROUND 15 KT THIS AFTERNOON. KSFO BRIDGE APPROACH... SIMILAR TO KSFO. MONTEREY BAY AREA TERMINALS...VFR CONDITIONS WITH MAINLY HIGH CLOUDS. TEMPORARY CIGS CAN`T BE RULED OUT AROUND SUNRISE THIS MORNING. LOW CONFIDENCE. LIGHT WINDS. && .MARINE...AS OF 09:30 AM PDT TUESDAY...MAINLY LIGHT TO LOCALLY MODERATE WINDS AND CALM SEAS ARE FORECAST THROUGH TONIGHT. THE STRONGEST WINDS WILL BE OVER THE NORTHERN SAN FRANCISCO BAY IN THE AFTERNOON...ESPECIALLY NEAR THE GOLDEN GATE BRIDGE AND ANGEL ISLAND. WINDS ARE EXPECTED TO INCREASE AND SHIFT TO THE NORTHWEST AFTER MIDWEEK. && .MTR WATCHES/WARNINGS/ADVISORIES... .TDAY...NONE. $$ PUBLIC FORECAST: RGASS AVIATION: CW MARINE: SIMS 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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