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

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000
FXUS66 KMTR 062051
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
151 PM PDT MON JUL 6 2015

.SYNOPSIS...A DEEP MARINE LAYER WILL REMAIN IN PLACE THROUGH
MIDWEEK AND RESULT IN WIDESPREAD NIGHT AND MORNING CLOUDS...PATCHY
FOG AND COASTAL DRIZZLE. TEMPERATURES WILL GENERALLY BE ON THE
COOL SIDE OF AVERAGE THROUGH THE WEEK AS AN UPPER LEVEL SYSTEM
APPROACHES THE CALIFORNIA COAST. THIS SYSTEM MAY ALSO TRIGGER
ISOLATED SHOWERS AND THUNDERSTORMS FROM WEDNESDAY AFTERNOON
THROUGH THURSDAY EVENING.

&&

.DISCUSSION...AS OF 01:50 PM PDT MONDAY...LOW CLOUDS OVER THE
REGION THIS MORNING MIXED OUT WELL THIS AFTERNOON WITH ONLY A
SMALL PATCH OF STRATUS SOUTH OF BIG SUR ALONG THE COAST.
ELSEWHERE...MOSTLY CLEAR SKIES WITH A FEW/SCT HIGH CLOUDS
STREAMING IN FROM THE MID/UPPER LEVEL LOW PRESSURE SYSTEM ABOUT
385 MILES WEST-NORTHWEST OF SAN FRANCISCO. VERY LITTLE CHANGE IS
EXPECTED THROUGH TUESDAY AS THE UPPER LEVEL SYSTEM IS FORECAST TO
REMAIN WELL WEST OF THE REGION. GIVEN THIS AND THE DEEP MARINE
LAYER IN PLACE...LOW CLOUDS WILL LIKELY REDEVELOP QUICKLY THIS
EVENING AND MAKE A PUSH INLAND OVERNIGHT. WHILE DRIZZLE IS ONCE
AGAIN POSSIBLE EARLY TUESDAY MORNING...THE MODELS SHOW IT BEING
MORE PATCHY THAN THIS MORNING. OVERALL WEATHER CONDITIONS ON
TUESDAY WILL BE SIMILAR TO TODAY WITH LOW CLOUDS MIXING OUT DURING
THE LATE MORNING HOURS.

THE UPPER LEVEL LOW WILL THEN BEGIN TO MOVE TOWARD THE CENTRAL
CALIFORNIA COAST LATE TUESDAY INTO WEDNESDAY. AS IT DOES...MID-
LEVEL MOISTURE IS EXPECTED TO WRAP AROUND THE LOW AND ADVECT
ACROSS THE REGION. THIS WILL COOL TEMPERATURES ALOFT AND HELP TO
DEEPEN OR AT LEAST MAINTAIN THE DEEP MARINE LAYER ALREADY IN PLACE
OVER THE REGION. THUS...GOOD INLAND PENETRATION OF LOW CLOUDS AND
PATCHY FOG WILL CONTINUE THROUGH MID/LATE WEEK. IN
ADDITION...SURFACE TEMPERATURES WILL BE ON A COOLING TREND THROUGH
THE REMAINDER OF THE WEEK WITH A COOLER AIR MASS MOVING OVER THE
WEST COAST.

THE MAIN FORECAST CHALLENGE CONTINUES TO BE THE POTENTIAL FOR
ELEVATED SHOWERS AND/OR THUNDERSTORMS. AS MENTIONED EARLIER...MID-
LEVEL MOISTURE WILL ADVECT OVER THE REGION WEDNESDAY AND THURSDAY
AS THE LOW APPROACHES. THIS COMBINED WITH INCREASED INSTABILITY
WILL RESULT IN A POTENTIAL FOR ISOLATED SHOWERS AND THUNDERSTORMS.
HOWEVER...THE TIMING AND POTENTIAL LOCATIONS WHERE THIS MAY OCCUR
REMAINS IN QUESTION GIVEN THE DIFFERENCES IN THE FORECAST MODELS
AND EVENTUAL TRACK OF THE SYSTEM. WITH THAT SAID...WILL KEEP A
MENTION OF SHOWERS AND THUNDERSTORMS IN THE FORECAST FROM
WEDNESDAY AFTERNOON THROUGH THURSDAY EVENING AS A HEADS-UP TO FIRE
AGENCIES AND ANY OTHERS THAT MAY BE CONCERNED OF CONVECTION. MID-
LEVEL MOISTURE MAY LINGER INTO FRIDAY MORNING WITH A SLIGHT CHANCE
OF SHOWERS OVER THE NORTH BAY.

THE MID/UPPER LEVEL SYSTEM WILL THEN LIFT TO THE NORTHEAST AND
BECOME ABSORBED IN THE MEAN FLOW FRIDAY INTO SATURDAY. THIS SHOULD
PUT AN END TO PRECIPITATION CHANCES REGION-WIDE FRIDAY NIGHT INTO
THE UPCOMING WEEKEND. THE FORECAST MODELS GENERALLY KEEP A BROAD
MID/UPPER LEVEL TROUGH ALONG MUCH OF THE WEST COAST LATE IN THE
PERIOD AND WILL LIKELY RESULT IN DRY WEATHER CONDITIONS AND
TEMPERATURES NEAR SEASONAL AVERAGES.

&&

.AVIATION...AS OF 10:55 AM PDT MONDAY... A WEAK UPPER LOW
LINGERING OFFSHORE WILL LEAD TO PREDOMINATELY ONSHORE FLOW AND VFR
CONDS TODAY. MARINE LAYER IS FORECAST TO DEEPEN TONIGHT AND SPREAD
INLAND SIMILAR TO YESTERDAYS EARLY ARRIVAL AND PERSIST AS LONG AS
OR SLIGHTLY LATER FOR TOMORROW MORNING AS UPPER LOW SHIFTS INLAND.

VICINITY OF KSFO... VFR TODAY WITH ONSHORE FLOW. SUST WINDS 15 KT
WITH GUSTS TO AROUND 20 KT THIS AFTERNOON. MVFR RETURNS AOA 05Z
TUE.

KSFO BRIDGE APPROACH... SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...VFR NORTH AND SOUTH MONTEREY BAY...
WITH MVFR THRU 19Z AT KWVI. ONSHORE FLOW SUST 10 KT WITH GUSTS TO
15 KT THIS AFTERNOON. EARLY RETURN OF LOW CIGS BY 01-02Z TUE.

&&

.MARINE...AS OF 10:43 AM PDT MONDAY...LIGHT WINDS AND SEAS ARE
EXPECTED THROUGH THE FORECAST PERIOD AS A WEAK LOW PRESSURE
LINGERS OFFSHORE.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...SF BAY UNTIL 9 PM

&&

$$

PUBLIC FORECAST: RGASS
AVIATION: DRP
MARINE: DRP


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