Small Craft Advisory 4, NWS Los Angeles, CA

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
830 PM PST SUN JAN 18 2015

.SYNOPSIS...
TEMPERATURES WILL FLUCTUATE UP AND DOWN SEVERAL DEGREES...BUT REMAIN
ABOVE NORMAL THROUGH MID WEEK...AS WEAK OFFSHORE FLOW STRENGTHENS
AND WEAKENS. LOW CLOUDS AND FOG COULD RETURN TO PARTS OF THE COAST
EARLY THIS WEEK AS WELL. WELL ABOVE NORMAL TEMPERATURES ARE EXPECTED
LATER IN THE WEEK AS A LARGE RIDGE OF HIGH PRESSURE AND STRONGER
OFFSHORE FLOW DEVELOPS.

&&

.SHORT TERM (TONIGHT-WED)...
UPPER LEVEL RIDGE OF HIGH PRESSURE CONTINUES TO FLATTEN TONIGHT...ALLOWING
HIGHER LEVEL CLOUDS TO CONTINUE STREAMING OVER THE AREA THROUGH
MONDAY. NEAR THE SURFACE...OFFSHORE GRADIENTS CONTINUE TO WEAKEN.
ACARS SOUNDING OVER LOS ANGELES SHOWING A RETURN OF A SHALLOW MARINE
LAYER THIS EVENING...AROUND 400 FEET. WITH THESE FACTORS IN MIND...THERE
IS AN INCREASED THREAT OF LOW CLOUDS AND DENSE FOG RETURNING
ALONG COASTAL AREAS...HOWEVER THE UPPER LEVEL HIGH CLOUDS MAY DISRUPT
THE LOW CLOUDS AT TIMES.  CURRENT SATELLITE IMAGERY AND SURFACE
OBSERVATIONS ALREADY SHOWING A RETURN OF LOW CLOUDS AND FOG ACROSS
PORTIONS OF THE CENTRAL COAST...ALONG WITH PATCHY LOW CLOUDS AND FOG
ACROSS THE SANTA BARBARA SOUTH COAST AND VENTURA COAST. DURING THE
OVERNIGHT HOURS...PATCHY LOW CLOUDS AND DENSE FOG WILL LIKELY EXPAND
TO THE LOS ANGELES COAST. OTHER AREA OF CONCERN TONIGHT WILL BE LOW
CLOUDS AND FOG THAT IS CURRENTLY OVER THE SAN JOAQUIN VALLEY
ADVECTING INTO THE INTERIOR VALLEYS OF SLO COUNTY OVERNIGHT FROM THE
EAST. TEMPERATURES WILL LIKELY NUDGE DOWN A FEW DEGREES DURING THE
NEXT COUPLE OF DAYS BUT STILL REMAINING ABOVE SEASONAL NORMALS.

*** FROM PREVIOUS DISCUSSION ***

A LONGWAVE RIDGE OVER THE WEST COAST WILL RESULT IN EFFICIENT
BLOCKING OF A SHORTWAVE TROUGH APPROACHING THE CALIFORNIA COAST
TUESDAY INTO WEDNESDAY. THE LATEST MODELS SHOW THE ENERGY SPLITTING
AS IT ENCOUNTERS THE WEST COAST RIDGE...DRAGGING A BAGGY TROUGH
ACROSS SOUTHWEST CALIFORNIA EARLY WEDNESDAY. THERE IS AN OUTSIDE
CHANCE OF LIGHT RAIN OVER THE AREA LATE TUESDAY NIGHT AND
WEDNESDAY...SO LOW IN FACT THAT PRECIP CHANCES ARE KEPT UNDER 10
PERCENT. MOISTURE WILL BE AN IMPORTANT LIMITING FACTOR AS A STREAM
OF SUBTROPICAL MOISTURE DEPICTED BY THE GFS REMAINS WELL SOUTH OF
THE AREA. THE GFS WOULD LIKE TO BRING THIS MOISTURE AROUND THE LOW
AND INTO SOUTHERN CALIFORNIA FROM THE NORTHEAST ON WEDNESDAY...BUT
PRECIPITABLE WATER AMOUNTS REMAIN LOW.

.LONG TERM (THU-SUN)...
HIGH PRESSURE ALOFT WILL BUILD IN OVER THE WEST COAST ON
THURSDAY...WITH A SURFACE HIGH OVER THE GREAT BASIN. THIS WILL SET
THE STAGE FOR OFFSHORE TRENDS THURSDAY AND FRIDAY...ALONG WITH A
WEAK WARMING TREND. THE NORTHEAST WINDS ARE EXPECTED TO BE
RELATIVELY WEAK AT THIS TIME...WITH PEAK GUSTS NEAR 35 MPH OVER THE
WIND-PRONE RIDGES AND CANYONS. FRIDAY INTO SATURDAY THE MEDIUM RANGE
MODELS SHOW AN INSIDE SLIDER CROSSING THROUGH THE CENTRAL GREAT
BASIN...FOLLOWED BY A FAIRLY STRONG UPPER RIDGE DEVELOPING OVER THE
CALIFORNIA COAST. THIS HAS THE POTENTIAL TO SET UP ANOTHER ROUND OF
SANTA ANA WINDS SATURDAY AND SUNDAY.

&&

.AVIATION...18/2345Z...

MARINE LAYER AT LAX AT 2330Z IS 400 FEET DEEP AND THE INVERSION TOP IS
AT 1700 FEET WITH A TEMP OF 20 DEGREES C.

UPPER LEVEL RIDGE OF HIGH PRESSURE WILL CONTINUE TO FLATTEN OVER THE
NEXT 24 HOURS ALLOWING FOR HIGHER LEVEL CLOUDS TO STREAM OVER THE
AREA. NEAR THE SURFACE...OFFSHORE FLOW CONTINUES TO WEAKEN GRADUALLY.
WITH A SHALLOW MARINE INVERSION AND WEAK ONSHORE TRENDS...THERE IS
A CHANCE OF LIFR CIGS DEVELOPING BY EARLY MONDAY MORNING ACROSS COASTAL
PORTIONS OF LA COUNTY...INCLUDING KLAX AND KLGB. HOWEVER...CONFIDENCE
IS LOW IN THESE CIGS DEVELOPING AS UPPER LEVEL CLOUDS MAY HELP INHIBIT
THE MARINE LAYER CLOUDS FROM FORMING. HIGH CONFIDENCE OF IFR CIGS
DEVELOPING ACROSS INTERIOR PORTIONS OF SLO COUNTY (INCLUDING KPRB) OVERNIGHT
AS EASTERLY LOW LEVEL FLOW ADVECTS MOISTURE IN FROM THE SAN JOAQUIN
VALLEY.

KLAX...THERE IS A CHANCE OF CIGS 002 AND VSBY 1SM BR BETWEEN
19/11-19/17Z OTHERWISE BKN 200 WITH PERIODS OF 5SM HZ.

KBUR...VFR CONDITIONS LIKELY THROUGH THE PERIOD.

&&

.MARINE...18/800 PM...
SMALL CRAFT ADVISORY CONDITIONS LIKELY LATE MONDAY AFTERNOON THROUGH
MONDAY NIGHT FOR OUTER WATERS NORTH AND WEST OF SAN MIGUEL ISLAND.
THE SCA CONDITIONS WILL LIKELY RETURN TUESDAY AFTERNOON AND EXTEND
FROM POINT PIEDRAS BLANCAS TO THE NORTHERN CHANNEL ISLANDS.
OTHERWISE A LOW PRESSURE SYSTEM CURRENTLY OVER THE WESTERN PACIFIC
WAS GENERATING SEAS OVER 40 FEET TODAY AND IS EXPECTED TO
CONTINUE GENERATING SEAS OVER 40 FEET THROUGH MONDAY EVENING AS IT
CONTINUES EAST OVER THE WESTERN AND CENTRAL PACIFIC. THE FETCH AREA
IS BETWEEN 280-300 DEGREES RELATIVE TO THE VENTURA COAST AND THE
SWELL WILL BEGIN TO ARRIVE THURSDAY AFTERNOON.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).

&&

PUBLIC...GOMBERG/SMITH
AVIATION/MARINE...GOMBERG/30
SYNOPSIS...SUKUP

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