Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 171211
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
515 AM PDT WED SEP 17 2014

...UPDATED AVIATION...MARINE AND BEACH DISCUSSIONS...

.SYNOPSIS...
IT STILL WILL BE HOT TODAY AWAY FROM THE COAST. LINGERING MID LEVEL
MOISTURE WILL ALLOW FOR A CHANCE OF SHOWERS AND THUNDERSTORMS OVER
EASTERN LOS ANGELES COUNTY LATE THIS MORNING THROUGH THIS EVENING.
AN APPROACHING TROUGH OF LOW PRESSURE WILL BRING SIGNIFICANT
COOLING TREND TO THE AREA THURSDAY THROUGH FRIDAY...WITH INCREASING
NIGHT THROUGH MORNING LOW CLOUDS AND FOG...AND SOME LOCAL DRIZZLE
POSSIBLE. UPPER LEVEL HIGH PRESSURE MAY BRING SOME WARMING TO THE
REGION LATE IN THE WEEKEND INTO EARLY NEXT WEEK.

&&

.SHORT TERM (TODAY-FRI)...PATCHY LOW CLOUDS ON THE CENTRAL COAST
THIS MORNING SHOULD BECOME MORE WIDESPREAD...AND WILL LIKELY PUSH
INTO THE SANTA YNEZ VALLEY BY MID MORNING. THERE WILL BE LOCAL DENSE
FOG...BUT LIKELY NOT WIDESPREAD ENOUGH FOR DENSE FOG ADVISORIES.
ELSEWHERE...SKIES SHOULD REMAIN MOSTLY CLEAR. GUSTY WINDS HAVE
DIMINISHED ACROSS SRN SBA COUNTY...SO WIND THE WIND ADVISORY AND THE
FLAG WARNING WILL BE ALLOWED TO EXPIRE. PRESSURE GRADIENTS WERE
STILL OFFSHORE THIS MORNING BUT WILL TURN ONSHORE THIS
AFTERNOON...AND ARE FORECAST TO BE AROUND 3 MB MORE ONSHORE THIS
AFTERNOON THAN THEY WERE ON TUESDAY. WITH HEIGHTS AND THICKNESSES
FALLING ACROSS THE REGION...AND TEMPS AT 950 MB FORECAST TO BE
3 TO 4 C LOWER THAN ON TUE. THIS SHOULD BRING SEVERAL DEGREES OF
COOLING TO MUCH OF THE REGION TODAY. HOWEVER...WITH THE WEAK
OFFSHORE FLOW TO START...TEMPS WILL LIKELY SOAR QUICKLY THIS
MORNING...SO MAX TEMPS MAY STILL REACH OR EXCEED 100 DEGREES IN THE
WARMEST VALLEY LOCATIONS. OVERALL...THOUGH...TODAY SHOULD BE
NOTICEABLY COOLER THAN IT WAS ON TUE.

THE TRICKIEST PART OF THE FORECAST WILL BE THE POTENTIAL FOR
CONVECTION. WITH GOOD MOISTURE CONTENT THROUGH THE ATMOSPHERE...ANY
THUNDERSTORM THAT DEVELOPS WILL LIKELY BRING HEAVY DOWNPOURS...AND
WITH VERY WEAK STEERING FLOW LATER THIS MORNING INTO THIS
AFTERNOON...ANY STORM WOULD BE VERY SLOW MOVING...RAISING THE
SPECTER OF FLASH FLOODING. THE WRF SHOWS DECENT INSTABILITY ACROSS
THE L.A. COUNTY MTNS...MAINLY ACROSS ERN L.A. COUNTY...AND
THE ADJACENT PORTIONS OF THE ANTELOPE VALLEY. IT ALSO SHOWS A
TONGUE OF HIGH 850 MB DEW POINTS OF 12 TO 15C ACROSS L.A. COUNTY...
AND OBSERVATIONS IN THE MTNS SUPPORT THIS. WITH THE HIGH 850 MB DEW
POINT LINGERING WELL INTO THE AFTERNOON...BLV THERE WILL BE ENOUGH
MOISTURE AND INSTABILITY TO ALLOW FOR SOME THUNDERSTORMS TO
DEVELOP...MAINLY ACROSS ERN L.A. COUNTY. AFTER COORDINATION WITH
SURROUNDING OFFICES...HAVE DECIDED TO ISSUE A FLASH FLOOD WATCH FOR
THE MTNS OF L.A. COUNTY AND THE ANTELOPE VALLEY...NOTING THAT THE
FOCUS IS EXPECTED TO BE OVER EASTERN SECTIONS. THE GFS IS QUITE A
BIT DRIER...AND WOULD SUGGEST LITTLE CONVECTIVE THREAT.
HOWEVER...ITS 850 MB DEW POINTS/MOISTURE LOOK TO BE TOO LOW...AND
IT SEEMS TO BE A BIT TOO FAST WITH THE APPROACHING TROUGH.
THEREFORE...HAVE LEANED TOWARD THE WRF FOR THIS FORECAST.

AN UPPER LOW WILL APPROACH THE NRN CA COAST TONIGHT AND THU...WITH
A TROUGH EXTENDING SOUTHWARD TO WEST OF THE FORECAST AREA. SWLY FLOW
ALOFT WILL SPREAD ACROSS THE REGION THIS EVENING...SHUNTING ANY MID
LEVEL MOISTURE AND CONVECTION EAST OF THE AREA. LOW LEVEL N-S
GRADIENTS WILL BE STRONG ENOUGH FOR SOME GUSTY N WINDS THRU AND
BELOW PASSES AND CANYONS OF THE SANTA YNEZ RANGE AND THE ADJACENT S
COAST OF SBA COUNTY...AND WINDS COULD GET CLOSE TO ADVISORY LEVELS
ONCE AGAIN. NIGHT THROUGH MORNING LOW CLOUDS AND FOG WILL BECOME
WIDESPREAD IN COASTAL AREAS TONIGHT...WITH THE EXCEPTION OF THE S
COAST OF SBA COUNTY...WHERE NLY FLOW WILL LIKELY KEEP SKIES MOSTLY
CLEAR. SOME STRATUS COULD EVEN PUSH INTO THE LOWER VALLEY LOCATIONS
FOR A FEW HOURS THU MORNING. WITH GOOD ONSHORE GRADIENT...SKIES MAY
HAVE A TOUGH TIME CLEARING NEAR THE COAST ON THU...ESPECIALLY N OF
PT CONCEPTION...WHERE THERE WILL ALSO BE SOME MID LEVEL CLOUDS
ASSOCIATED WITH A WEAKENING SFC FRONT. AT THIS POINT...DO NOT EXPECT
ANYTHING MORE THAN A FEW SPRINKLES WITH THE DYING FRONT ACROSS
NORTHERN SECTIONS. WITH CONSIDERABLE HEIGHT FALLS AND INCREASING
ONSHORE FLOW...EXPECT SIGNIFICANT COOLING ACROSS THE ENTIRE AREA ON
THU...ESPECIALLY IN THE VLYS...WHERE MAX TEMPS MAY BE DOWN MORE
THAN 15 DEGREES FROM THOSE REACHED TODAY IN SOME AREAS.

ALL MODELS SHOW THE UPPER LOW DROPPING DOWN THE COAST OF CA THU
NIGHT AND FRI MORNING...REACHING A POSITION NEAR POINT CONCEPTION
FROM FRI AFTERNOON. EXPECT A RATHER DEEP MARINE LAYER THU NIGHT/FRI
MORNING...WITH CLOUDS POSSIBLY UP TO THE COASTAL SLOPES.  THERE
COULD BE SOME DRIZZLE OR EVEN A LITTLE LIGHT RAIN FRI
MORNING...ESPECIALLY ACROSS THE FOOTHILLS OF L.A. COUNTY AS SOME LOW
LEVEL LIFT DEVELOPS IN THE INCREASINGLY CYCLONIC FLOW. THERE MAY BE
ONLY PARTIAL CLEARING ON FRIDAY. MAX TEMPS WILL BE DOWN A FEW MORE
DEGREES IN MOST AREAS...DOWN TO BELOW NORMAL LEVELS IN MOST AREAS
FOR THE FIRST TIME IN SINCE THE 4TH OF THE MONTH.

.LONG TERM (SAT-TUE)...THE UPPER LOW WILL REMAIN NEARLY STATIONARY
NEAR POINT CONCEPTION FRI NIGHT AND SAT. EXPECT THE DEEP MARINE
LAYER TO CONTINUE...WITH PLENTY OF NIGHT THRU MORNING LOW CLOUDS IN
COASTAL AND VALLEY AREAS...POSSIBLY UP TO THE COASTAL SLOPES ONCE
AGAIN. SOME DRIZZLE OR LIGHT SHOWERS WILL REMAIN POSSIBLE. IT WILL
BE COOL AGAIN ON SATURDAY ACROSS THE REGION. THE UPPER LOW WILL LIFT
INTO CENTRAL CA SAT NIGHT AND SUN. EXPECT BETTER CLEARING ON
SUNDAY...AND MAX TEMPS WILL LIKELY BE UP A FEW DEGREES IN MOST
AREAS. AND UPPER RIDGE WILL BUILD INTO THE REGION ON MONDAY...WITH
ADDITIONAL WARMING LIKELY...AND A REDUCTION IN NIGHT THROUGH MORNING
STRATUS. SOME ADDITIONAL WARMING IS LIKELY ON TUE AS THE RIDGE
AMPLIFIES A BIT...AND IF LOW OFFSHORE FLOW DEVELOPS...WARMING MAY BE
SIGNIFICANT.


&&

.AVIATION...17/0510Z.
N OF POINT CONCEPTION...
LOW CONFIDENCE WITH 12Z TAF AS KSMX/KSBP REMAIN CLEAR BUT COULD GO
LIFR BETWEEN 13Z AND 16Z. 50 PERCENT CHANCE FOR LIFR CONDS FOR
CENTRAL COAST BETWEEN 13Z-16Z. HIGH CONFIDENCE WITH 12Z KPRB TAF.

S OF POINT CONCEPTION...
HIGH CONFIDENCE WITH 12Z TAF THROUGH 04Z THIS EVENING FOR VFR CONDS.
LOWER CONFIDENCE FOR RETURN OF STRATUS AFTER 04Z AS IFR CIGS WILL BE
LIKELY FOR COASTAL AREAS OF LOS ANGELES AND VENTURA COUNTIES. LESS
LIKELY FOR KSBA DUE TO SUNDOWNER WINDS BETWEEN 22Z-07Z. BUT 30
PERCENT CHANCE FOR IFR CIGS AFTER 10Z THU MORNING AT KSBA.

KLAX...HIGH CONFIDENCE IN THE 12Z TAF. THERE IS 10 PERCENT CHANCE OF
IFR CONDS BETWEEN 12Z AND 15Z.

KBUR...VERY HIGH CONFIDENCE IN THE 12Z TAF WITH VFR CONDITIONS THRU
THE NEXT 24 HOUR PERIOD.

&&

.MARINE...

17/445 AM

OUTER WATERS...SMALL CRAFT ADVISORIES IN EFFECT FOR OUTER WATERS
FROM POINT POINT SAL AND AREAS SOUTH THROUGH EARLY THURSDAY MORNING.
MODERATE CONFIDENCE FOR PZZ670 TO REMAIN BELOW WIND ADVISORY
THRESHOLDS THROUGH THIS WEEKEND. 60 PERCENT CHANCE FOR SMALL CRAFT
ADVISORIES FOR PZZ673-676 FOR THURSDAY AFTERNOON AND EVENING.

THE WESTERN HALF OF THE SANTA BARBARA CHANNEL WILL SEE LOCAL
NORTHWEST GUSTS TO 25 KT LATE THIS AFTERNOON AND EVENING. 30 PERCENT
CHANCE THAT A SMALL CRAFT ADVISORY WILL BE NEEDED. OTHERWISE NO
OTHER ISSUES THROUGH THIS WEEKEND.

&&

.BEACHES...

17/445 AM

A LONG PERIOD (16-17+ SECOND) SOUTHERN HEMISPHERE SWELL WILL
CONTINUE TO MOVE THROUGH THE COASTAL WATERS. SWELL HEIGHT WILL
REMAIN BETWEEN 1 AND 2 FEET...BUT WITH A LONG PERIOD...EXPECT SURF 2
TO 4 FEET WITH LOCAL SETS TO 5 FEET ACROSS SOUTHWEST FACING BEACHES.
THE MAIN ISSUE WILL BE SIGNIFICANT AMOUNT OF RIP CURRENT ACTIVITY
THROUGH AT LEAST FRIDAY.

THERE IS NO LONGER A THREAT OF SWELLS FROM HURRICANE ODILE.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH (SEE LAXFFALOX)
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
HIGH RIP CURRENT RISK (SEE LAXSRFLOX).

&&

$$

PUBLIC...DB
AVIATION/MARINE...CK
SYNOPSIS...DB

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