Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 181045 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
340 AM PDT SAT APR 18 2015

.SYNOPSIS...

EXPECT A MODEST COOLING TREND THROUGH MONDAY...WITH MORE SIGNIFICANT
COOLING EARLY NEXT WEEK ACROSS SOUTHWESTERN CALIFORNIA OVER THE NEXT
SEVERAL DAYS AS ONSHORE FLOW INCREASES AND BRINGS NIGHT THROUGH
MORNING LOW CLOUDS BACK TO THE COAST AND SOME COASTAL VALLEYS
THROUGH AT LEAST MID WEEK. THERE WILL BE A SLIGHT CHANCE FOR
THUNDERSTORMS ACROSS SOME LOCAL MOUNTAIN AREAS EARLY NEXT
WEEK. ANOTHER UPPER LOW WILL BRING A MORE WIDESPREAD CHANCE FOR
SHOWERS BY MID WEEK. AN ISOLATED THUNDERSTORM CANT BE RULED OUT AS
WELL WITH THIS UPPER LOW.

&&

.SHORT TERM (TODAY-MON)...SKIES WERE MOSTLY CLEAR ACROSS THE
FORECAST AREA THIS MORNING...WITH THE EXCEPTION OF PATCHY DENSE FOG
ACROSS THE CENTRAL COAST. THE LOW CLOUDS AND FOG WHICH HAS FILLED IN
THE ENTIRE COASTAL WATERS N OF POINT CONCEPTION WILL CONTINUE TO
TREK SOUTHWARD TOWARDS THE SANTA BARBARA CHANNEL THIS MORNING.  THE
INVERSION REMAINS QUITE SHALLOW WHICH WILL ALLOW FOR THE PATCHY
DENSE FOG TO PERSIST ACROSS THE COASTAL WATERS AND LINGER NEAR THE
CENTRAL COAST INTO THE EARLY AFTERNOON HOURS. ONSHORE FLOW WILL
STRENGTHEN TODAY WHICH WILL BRING COOLER MOIST AIR BACK TO MUCH OF
THE COASTAL AREAS TODAY. EXPECT 3 TO 5 DEGREES OF COOLING ACROSS
MUCH OF THE FORECAST AREA TODAY. SKIES SHOULD REMAIN MOSTLY CLEAR
OVER LAND TODAY EXCEPT FOR THE IMMEDIATE CENTRAL COAST.

BY TONIGHT...LOW CLOUDS AND PATCHY FOG SHOULD BECOME MORE WIDESPREAD
ACROSS MUCH OF THE COASTAL AREAS AND INTO THE SANTA YNEZ VALLEY AND
LIKELY INTO THE SAN GABRIEL AND PORTIONS OF THE SAN FERNANDO VALLEY
BY SUNDAY MORNING. HIGH TEMPS WILL CONTINUE TO TREND DOWNWARD AS THE
COMBINATION OF MODERATE ONSHORE SURFACE FLOW AND A MORE TROUGHY
UPPER LVL PATTERN SETS UP THROUGH NEXT WEEK.

FOR SUNDAY THERE WILL CONTINUE TO BE SOME WIDESPREAD COOLING WITH
LOW CLOUDS LIKELY LINGERING ACROSS SOME BEACH AREAS INTO THE
AFTERNOON HOURS. MODELS ARE ALSO PICKING UP ON SOME MARGINAL
INSTABILITY OVER THE VENTURA AND LOS ANGELES COUNTY MOUNTAINS THIS
AFTERNOON. THERE WILL BE VERY LITTLE IN THE WAY OF MID LEVEL
MOISTURE TO TAP INTO SUNDAY...BUT THERE WILL BE A FEW FLAT CU
BUILD-UPS IN THE LOCAL MOUNTAINS. EXPECT THE RETURN OF NIGHT THROUGH
MORNING LOW CLOUDS SUNDAY NIGHT INTO MONDAY. AN UPPER LEVEL TROUGH
WILL CONTINUE TO DEEPEN...AND MODELS ONCE AGAIN ARE PICKING UP ON
SOME INSTABILITY OVER THE MOUNTAINS MONDAY AFTERNOON...ESPECIALLY
THE VENTURA COUNTY MOUNTAINS WHERE THERE LOOKS TO BE A POOL OF MID
LEVEL MOISTURE TO TAP INTO. IF AN ISOLATED STORM IS ABLE TO
INITIATE...THERE WILL BE ENOUGH LIFT WITH ~600 J/KG OF CAPE THAT
ELEVATED THUNDERSTORMS ARE POSSIBLE. THE MAIN IMPACT WOULD BE
ISOLATED DRY LIGHTNING AND GUSTY OUTFLOW WINDS. MEANWHILE...COAST
AND VALLEYS WILL CONTINUE THE COOLING TREND WITH MOST INLAND COASTAL
AREAS AND VALLEYS WILL BE IN THE LOWER TO MID 70S.

.LONG TERM (TUE-FRI)...BOTH THE GFS AND ECMWF ARE IN FAIRLY GOOD
AGREEMENT WITH CONTINUING AN UPPER LEVEL TROUGH PERSISTING OVER THE
FORECAST AREA THROUGH ALL OF NEXT WEEK. THERE WILL BE ANOTHER SLIGHT
CHANCE OF ELEVATED THUNDERSTORMS OVER THE VENTURA/SBA COUNTY
MOUNTAINS ON TUESDAY AFTERNOON AND EVENING WITH PARTLY CLOUDY SKIES
LIKELY INCREASING OVER THE REGION. BOTH MODELS CONTINUE TO SHOW THE
UPPER LOW DIGGING FARTHER SOUTH AND CUTOFF OVER THE SOUTHERN
CALIFORNIA COASTAL WATERS ON WEDNESDAY AND THURSDAY. AS HAS BEEN
TYPICAL MOST OF THIS PAST WINTER...THE UPPER LOW WILL MAKE IT VERY
DIFFICULT TO PIN POINT WHEN AND WHERE THE PRECIPITATION WILL OCCUR.
WITH 500 MB TEMPS EXPECTED TO BE AROUND -25 DEGREES CELSIUS NEAR THE
CENTER OF THE LOW...THERE WILL BE THE POSSIBILITY OF ISOLATED
THUNDERSTORMS OVER THE REGION. AT THIS POINT WILL HOLD OFF ON ADDING
THUNDER. BUT AS WE GET CLOSER TO THIS SCENARIO...THERE IS A GOOD
CHANCE THAT SOME MENTION OF "SLIGHT CHANCE THUNDERSTORMS" WILL BE
ADDED. SNOW LEVELS WILL ALSO BE LOWER FOR THIS TIME OF YEAR...AROUND
5000 FT...WEDNESDAY INTO WEDNESDAY EVENING...THEN LOWERING TO AROUND
4000 FT NEAR THE GRAPEVINE. WEDNESDAY NIGHT INTO THURSDAY MORNING.
WE ARE NOT EXPECTING MUCH IN THE WAY OF PRECIP WITH THIS
SYSTEM...EXCEPT THERE COULD BE BRIEF PERIODS OF HEAVY RAIN WITH ANY
THUNDERSTORMS.

&&

.AVIATION...18/1120Z

AT 0853Z THERE WAS A SURFACE BASED INVERSION AT KLAX. THERE TOP OF
THE INVERSION WAS AT 2100 FEET WITH A TEMPERATURE OF 19 CELSIUS.

STRATUS WILL AFFECT THE IMMEDIATE CENTRAL COAST THROUGH
MID MORNING...WITH LIFR TO VLIFR CONDS. ELSEWHERE...EXPECT VFR CONDS
THROUGH THIS EVENING. STRATUS SHOULD PUSH INTO COASTAL AREAS BY LATE
EVENING...REACHING THE VLYS LATE TONIGHT. CONDS SHOULD BE MOSTLY IFR
TO LIFR.

KLAX...HIGH CONFIDENCE IN THE 12Z TAF WITH VFR CONDS THROUGH THIS
EVENING. THERE IS A 20 PERCENT CHANCE THAT STRATUS WILL ARRIVE AS
EARLY AS 06Z.

KBUR...HIGH CONFIDENCE IN THE 12Z TAF WITH VFR CONDS THROUGH THIS
EVENING. THERE IS A 20 PERCENT CHANCE THAT STRATUS WILL NOT ARRIVE
UNTIL AFTER 12Z SUNDAY.

&&

.MARINE...18/300 AM...UPDATED SHORTLY

WINDS WERE BELOW SCA LEVELS ACROSS MOST OF THE OUTER WATERS...BUT
LOCAL SCA LEVEL GUSTS ARE EXPECTED THROUGH TONIGHT. THERE IS A 20
PERCENT CHANCE THAT SCA LEVEL WINDS WILL BECOME WIDESPREAD ENOUGH
TO REQUIRE ADVISORIES ACROSS PORTIONS OF THE OUTER WATERS THIS
AFTERNOON AND EVENING.

A MARINE WEATHER STATEMENT IS IN EFFECT FOR AREAS OF DENSE FOG FOR
THE OUTER WATERS AND NORTHERN SECTIONS OF THE INNER WATERS. DENSE
FOG SHOULD BECOME PATCHY IN NATURE BY AFTERNOON.

&&

.FIRE WEATHER...17/1215 PM
OFFSHORE WINDS MUCH LIGHTER ACROSS DISTRICT THIS MORNING...WITH
FASTER ONSET OF ONSHORE WINDS ACROSS THE COAST AND SOME COASTAL
VALLEYS AS OF NOON. ONSHORE WINDS EXPECTED TO SPREAD ACROSS ALL
VALLEY AREAS THROUGH THE AFTERNOON...REACHING THE MOUNTAINS AND
ANTELOPE VALLEY BETWEEN 2 PM AND 6 PM. HIGH RESOLUTION WRF MODEL
INDICATING STRONGEST ONSHORE WIND PUSH EXTENDING FROM SANTA CLARITA
VALLEY THROUGH HIGHWAY 14 CORRIDOR INTO THE ANTELOPE VALLEY...WHERE
GUSTS BETWEEN 20 AND 25 MPH WILL BE COMMON...AND ISOLATED GUSTS AS
HIGH AS 30 MPH IN THE FOOTHILLS OF THE ANTELOPE VALLEY.
MEANWHILE...A WARM AND DRY AIR MASS REMAINS IN PLACE ACROSS THE
REGION TODAY. MANY INTERIOR SECTIONS WILL SEE HIGH TEMPERATURES IN
THE 80S TODAY WITH HUMIDITIES BETWEEN 7 AND 12 PERCENT. THE
COMBINATION OF GUSTY ONSHORE WINDS...WARM TEMPERATURES...AND LOW
HUMIDITIES WILL BRING ELEVATED FIRE DANGER TO THE
VALLEYS...MOUNTAINS...AND ANTELOPE VALLEY THIS AFTERNOON AND
EVENING. A SLIGHTLY STRONGER ONSHORE PUSH IS EXPECTED FOR SATURDAY
AFTERNOON AND EVENING. WHILE HUMIDITIES WILL BE SLIGHTLY HIGHER
TOMORROW...THERE WILL STILL CONTINUE TO BE AN ELEVATED FIRE DANGER
ACROSS THE MOUNTAINS AND ANTELOPE VALLEY WHERE HUMIDITIES BETWEEN 10
AND 20 PERCENT WILL BE COMMON.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
HIGH SURF ADVISORY (SEE LAXCFWLOX).
MARINE WEATHER STATEMENT (SEE LAXMWSLOX).

&&

$$

PUBLIC...KAPLAN
AVIATION/MARINE...DB

WWW.WEATHER.GOV/LOSANGELES







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