Small Craft Advisory 28, NWS San Francisco Bay Area, CA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1100 AM PDT MON APR 20 2015

.SYNOPSIS...COOL CONDITIONS WILL PERSIST NEAR THE COAST TODAY WITH
WARM TEMPERATURES EXPECTED INLAND. TEMPERATURES COOL SLIGHTLY
REGION-WIDE BEGINNING TUESDAY AS A SERIES OF WEAK UPPER LEVEL
SYSTEMS PUSH ACROSS THE REGION. THESE WEAK WEATHER SYSTEMS WILL
PRODUCE A SLIGHT CHANCE OF SHOWERS AT TIMES TUESDAY THROUGH
THURSDAY...BUT MAINLY OVER THE INLAND MOUNTAINS.

&&

.DISCUSSION...AS OF 9:12 AM PDT MONDAY...DEEP MARINE LAYER IN
PLACE THIS MORNING TO AROUND 2500 FEET ALONG THE COAST WITH
STRATUS HAVING OVERSPREAD NEARLY ALL VALLEYS ACROSS THE DISTRICT
BELOW THIS ELEVATION. A WEAK UPPER LOW WEST OF LOS ANGELES WILL
KEEP THE MARINE LAYER DEEP WITH ONSHORE FLOW IN PLACE TODAY.
EXPECT FAIRLY SLOW BURN-OFF OF THE LOW CLOUDS TODAY GIVEN THE DEEP
LAYER WITH LITTLE OR NO CLEARING NEAR THE COAST AND SOME PARTS OF
THE BAY.

UPPER LOW OVER SOUTHERN CALIFORNIA WONT MOVE MUCH THROUGH WEDS
KEEPING CONDITIONS FAIRLY STATIC WITH A DEEP MARINE LAYER AND NEAR OR
BELOW NORMAL TEMPS. THIS FEATURE WILL HELP TO GENERATE AFTERNOON
SHOWERS AND T-STORMS OVER THE SIERRA AND OTHER HIGH MOUNTAINS OF
THE STATE BUT NOT EXPECTING ANY ACTIVITY OVER THE BAY AREA
HILLS...EXCEPTION BEING SOME LOCALIZED NIGHT AND MORNING DRIZZLE
DUE TO A DEEP MARINE LAYER.

MID AND LONG RANGE MODELS KEEP THE MAIN STORM TRACK JUST NORTH OF
THE BAY AREA. THE SYNOPTIC PATTERN LOOKS TO REMAIN FAIRLY ACTIVE
BUT AT THIS TIME IT LOOKS LIKE MOST RAINS WILL STAY ACROSS FAR
NORTHERN CALIFORNIA AND POINTS NORTHWARD.

&&

.PREV DISCUSSION...AS OF 4:37 AM PDT MONDAY...ONSHORE FLOW AND A
PERSISTENT MARINE LAYER GREATER THAN 2KFT DEEP HAS ALLOWED FOR LOW
CLOUDS TO ONCE AGAIN DEVELOP WELL INLAND INTO MOST VALLEY
LOCATIONS THIS MORNING. THIS HAS HELD OVERNIGHT TEMPERATURES IN
THE LOW/MID 50S REGION-WIDE. MEANWHILE...A WEAK MID/UPPER LEVEL
LOW PRESSURE SYSTEM CONTINUES TO DROP SOUTHWARD OFF OF THE CENTRAL
COAST AND WILL APPROACH THE SOUTHERN CALIFORNIA COAST DURING THE
NEXT 24 HOURS OR SO. AS THIS SYSTEM LINGERS OFF OF THE
COAST...WEATHER CONDITIONS TODAY WILL BE A NEAR REPEAT OF THOSE ON
SUNDAY. THUS...COOL TEMPERATURES NEAR THE COAST WHILE INLAND AREAS
ONCE AGAIN WARM INTO THE 70S AND LOWER 80S. IN ADDITION...THE
FORECAST MODELS KEEP THE BEST MID-LEVEL MOISTURE ASSOCIATED WITH
THIS SYSTEM WELL INLAND TODAY. WITH THAT...WILL MAINTAIN A DRY
FORECAST THROUGH THIS AFTERNOON/EVENING.

AS THE MARINE LAYER DEEPENS OVERNIGHT...PATCHY FOG AND DRIZZLE
WILL BE POSSIBLE ALONG THE COAST BY EARLY TUESDAY MORNING.
DAYTIME TEMPERATURES WILL FINALLY COOL INLAND THROUGH MIDWEEK AS
850MB CONDITIONS COOL AHEAD OF AN APPROACHING UPPER LEVEL TROUGH.
THE FORECAST MODELS CONTINUE TO STRUGGLE ON HOW MUCH MOISTURE
WILL BE ADVECTED INTO THE REGION WITH THIS SYSTEM...AND IF THE
ATMOSPHERE WILL BECOME UNSTABLE ENOUGH FOR SHOWERS/THUNDERSTORMS
TO DEVELOP OVER THE INLAND HILLS/MOUNTAINS. FOR NOW...WILL KEEP A
SLIGHT CHANCE OF SHOWERS AND THUNDERSTORM OVER THE MOUNTAINS OF
SAN BENITO COUNTY FOR TUESDAY AFTERNOON/EVENING AND SHOWERS OVER
MUCH OF THE HIGHER TERRAIN ON WEDNESDAY. AS A BROAD MID/UPPER
LEVEL TROUGH REMAINS OVER MUCH OF THE WEST COAST THROUGH LATE
WEEK WITH WEAK DISTURBANCES MOVING ACROSS THE REGION...CANNOT
RULE OUT A FEW SHOWERS OVER THE INLAND HILLS/MOUNTAINS THROUGH
THURSDAY. THE MEDIUM RANGE MODELS NOW SHOW DRY CONDITIONS
RETURNING TO THE REGION FOR FRIDAY AS THE UPPER LEVEL TROUGH AXIS
SHIFTS INLAND. HAVING SAID ALL THAT...MOST LOCATIONS WILL SEE
LITTLE TO NO RAINFALL THROUGH LATE WEEK.

MUCH OF THE UPCOMING WEEKEND IS NOW FORECAST TO REMAIN DRY WITH
THE UPPER LEVEL STORM TRACK WELL TO THE NORTH. HOWEVER...WILL
CARRY A SLIGHT CHANCE OF PRECIPITATION OVER THE NORTH BAY SUNDAY
INTO MONDAY AS THE 12Z GFS PUSHES A SYSTEM INTO THE PACIFIC
NORTHWEST WITH TRAILING MOISTURE ALONG A FRONTAL BOUNDARY
DROPPING SOUTHWARD. MEANWHILE...THE CMC AND ECMWF MAINTAIN DRY
WEATHER CONDITIONS FOR LATE IN THE FORECAST PERIOD WITH WEAK
RIDING OVER CENTRAL CALIFORNIA. OVERALL...CHANCES FOR MEASURABLE
RAINFALL OVER THE REGION THROUGH THE END OF APRIL ARE LOOKING
MINIMAL AT BEST.

&&

.AVIATION...AS OF 11:00 AM PDT MONDAY...STILL HAVE WIDESPREAD
CLOUDS ACROSS A GOOD PORTION OF OUR AREA ALTHOUGH LAST FEW FRAMES
SHOW IT IS DEFINITELY DIMINISHING. FOR THE TAF PACKAGE ONLY MADE A
FEW MINOR CHANGES TO THE BURN-OFF TIMES AND CONDITIONS FOR TODAY.
WOULD EXPECT ALL TERMINALS TO BE BACK TO VFR BY 20Z. WIND WILL
PICK UP OVER THE AFTERNOON WITH TYPICAL SEA BREEZES EXPECT. SPEEDS
SHOULD GENERALLY BE UNDER 15 KT. MVFR TO POSSIBLE IFR RETURNS
TONIGHT. WITH A DEEP MARINE LAYER PLUS WIND EXPECTED TO STAY 270
TO 290 FORECAST CALLS FOR VRF BREAK-OUT TO BE ABOUT THE SAME OR
EVEN AN HOUR OR TWO LATER FOR TOMORROW. OVERALL MODERATE
CONFIDENCE.

VICINITY OF KSFO...SATELLITE AND CAMS SHOW CLOUDS STARTING TO THIN
OUT JUST TO THE SOUTH WITH BKN-OVC MVFR CIGS FORECAST TIL 19Z.
WESTERLY WINDS ARE LIKELY TO REMAIN UNDER 20 KNOTS TODAY. MVFR
RETURNS AROUND 04Z. MODERATE TO HIGH CONFIDENCE FOR TODAY.

SFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...IFR CIGS EXPECTED 19-20Z FOLLOWED BY
PARTIAL CLEARING FOR THE AFTERNOON HOURS. PERSISTENCE FORECAST FOR
THE EVENING...STRATUS IS LIKELY TO RETURN EARLY BETWEEN 01 AND
02Z.

&&

.MARINE...AS OF 08:53 AM PDT MONDAY...NORTHWESTERLY WINDS WILL BE
ON THE INCREASE STARTING TOMORROW AS HIGH PRESSURE BUILDS IN FROM
THE NORTH. THE BIGGEST IMPACT WILL BE FOR ZONES NORTH OF POINT
REYES.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...SF BAY NORTH OF THE BAY BRIDGE

&&

PUBLIC FORECAST: RWW
AVIATION: BELL
MARINE: BELL

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