807 
FXUS66 KLOX 122054
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
150 PM PDT FRI APR 12 2013

.SYNOPSIS...

COOLER THAN NORMAL TEMPERATURES EXPECTED THROUGH EARLY NEXT WEEK AS 
A LOW PRESSURE AREA DEVELOPS ALONG THE WEST COAST. BREEZY AT 
TIMES...ESPECIALLY IN THE ANTELOPE VALLEY. A DEEPENING MARINE LAYER 
WILL RESULT IN LIMITED AFTERNOON CLEARING FOR COASTAL AREAS. DRIZZLE 
OR LIGHT RAIN POSSIBLE ACROSS LA AND VENTURA COUNTY MONDAY MORNING. 
DAYTIME HIGHS WILL DROP TO 5-10 DEGREES BELOW NORMAL SUNDAY AND 
MONDAY.

&&

.SHORT TERM (TODAY-MON)...NICE MARINE LYR CLEARING MOST AREAS TODAY 
AS A LITTLE OFFSHORE TREND IN THE GRADIENTS DEVELOPED BEHIND A WEAK 
TROF THAT PASSED THROUGH LAST NIGHT. DESPITE THAT TEMPERATURES TODAY 
GENERALLY RAN CLOSE TO OR A FEW DEGREES BELOW THURSDAY'S LEVELS. A 
LITTLE INCREASE IN HEIGHTS TODAY BEHIND THE TROF SHOULD RESULT IN A 
SLIGHT DECREASE IN MARINE LYR DEPTH, BUT OVERALL COVERAGE EXPECTED 
TO BE SIMILAR.

OVER THE WEEKEND A TROF WILL START TO DIVE SOUTH ALONG THE WEST 
COAST. THIS WILL BE BRING ABOUT A DEEPENING MARINE LYR AND STRONGER 
ONSHORE FLOW. WE WILL FEEL THE EFFECTS OF THE LATTER AS EARLY AS 
SATURDAY AS THE ANTELOPE VALLEY SEES A RATHER SUBSTANTIAL INCREASE 
IN AFTERNOON WINDS. WITH LAX-DAG GRADIENT UP TO ALMOST 9MB IN THE 
AFTERNOON WINDS SHOULD EXCEED ADVISORY LEVELS AT LEAST IN THE 
FOOTHILL AREAS (LAKE PALMDALE, POPPY PARK, ETC.). THE STRONG ONSHORE 
TRENDS WILL ALSO LIKELY MAKE FOR A MUCH SLOWER CLEARING DAY AT LEAST 
FOR THE COAST AND I SUSPECT THAT MANY BEACHES FROM SBA TO REDONDO 
WILL STRUGGLE TO CLEAR AT ALL. HOWEVER, OUTSIDE OF THE BEACHES AND 
THE ANTELOPE VALLEY, SATURDAY SHOULD BE A PRETTY NICE DAY BUT A FEW 
DEGREES COOLER THAN TODAY. 

THE TROF CONTINUES TO SLIDE SOUTH SUNDAY INTO MONDAY, RESULTING IN 
FURTHER DEEPENING OF THE MARINE LYR AND STRENGTHENING OF THE ONSHORE 
FLOW. BY SUNDAY LAX-DAG GRADIENT OVER 10MB SHOULD YIELD WIDESPREAD 
ADVISORY LEVEL WINDS IN THE AV, GUSTING TO AROUND 50 MPH IN AREAS. 
MUCH SLOWER MARINE LYR CLEARING, POSSIBLY LITTLE IF ANY CLEARING 
SOUTH OF PT CONCEPTION, ESPECIALLY ON MONDAY. DRIZZLE OR LIGHT RAIN 
A STRONG POSSIBILITY BY MONDAY, ESPECIALLY IN LA COUNTY. DAYTIME 
HIGHS FALLING TO 5-10 DEGREES BELOW NORMAL BY MONDAY.

.LONG TERM (TUE-FRI)...MODELS DIFFER WITH REGARD TO HOW FAR WEST THE 
TROF WILL DIG, THOUGH THE MAJORITY SOLUTION SEEMS TO FAVOR A MORE 
WESTERLY TRAJECTORY. THE ONLY HOLDOUTS CONTINUE TO BE THE 
OPERATIONAL GFS AND A FEW OF THE ENSEMBLE MEMBERS WHICH TRACK IT 
FARTHER EAST AND FASTER. EVEN THE NAM, WHICH ONLY GOES OUT TO MONDAY 
AFTERNOON, LOOKS VERY SIMILAR TO THE EURO. THIS MAKES THE FORECAST 
PROBLEMATIC IN A COUPLE WAYS. THE FARTHER WEST SOLUTION WOULD RESULT 
IN STRONGER WINDS ACROSS THE AREA MONDAY NIGHT INTO TUESDAY AND 
WOULD ALSO DELAY THE WARMING TREND NEXT WEEK. EITHER WAY, THOUGH, 
PRETTY BREEZY MOST AREAS EARLY NEXT WEEK, THOUGH NOT EXPECTING TO 
SEE THE KIND OF WIND WE SAW LAST MONDAY. 

OPTED TO TREND BACK DAYTIME HIGHS NEXT WEEK BASED ON THE SLOWER TROF 
MOVEMENT FAVORED BY THE MAJORITY OF THE MODELS TODAY. BY WEDNESDAY 
THERE ARE HUGE DIFFERENCES IN THE FORECAST HIGHS BETWEEN THE GFS AND 
THE EC. THE GFS HAS A DECENT OFFSHORE FLOW WITH THICKNESSES IN THE 
MID 560S WHILE THE EURO IS STILL ONSHORE WITH THICKNESSES IN THE LOW 
540S. THIS AMOUNTS TO POTENTIALLY 20 DEGREES OF HIGH TEMPERATURE 
DIFFERENCE BETWEEN THE MODELS IN SOME PLACES SO DEFINITELY NOT AN 
EASY FORECAST.

&&

.AVIATION... 12/1800Z
MODERATE TO HIGH CONFIDENCE IN 18Z TAFS. EXPECT CLEARING OF MARINE 
CIGS AT ALL SITES BY 21Z...ALTHOUGH TIMING COULD DIFFER +/- 1 HR 
FROM TAF TIMES. HIGH CONFIDENCE THAT MARINE LAYER WILL DEEPEN 
OVERNIGHT INTO EARLY SATURDAY...WITH STRATUS CLOUDS AFFECTING ALL 
COAST AND VALLEY SITES...BUT LOWER CONFIDENCE IN TIMING AND HEIGHT 
OF CIGS. EXPECT GENERALLY IFR CONDS FOR KSBA AND SITES N OF PT 
CONCEPTION...AND MVFR CONDS FURTHER SOUTH. GUSTY ONSHORE WINDS WILL 
AFFECT KPMD AND KWJF DURING THE AFTERNOON AND EVENING HOURS. 

KLAX...MODERATE TO HIGH CONFIDENCE IN 18Z TAF. MARINE CIGS EXPECTED 
TO RETURN TO THE SITE AROUND 03Z...BUT TIMING COULD DIFFER BY +/- 2 
HOURS. 

KBUR...MODERATE CONFIDENCE IN 18Z TAF. THE TIMING OF MARINE CIGS 
RETURN TO THE SITE MAY DIFFER BY +/- 2 HOURS OR MORE FROM TAF TIMES. 
20% CHANCE CONDS WILL FALL INTO THE IFR CATEGORY OVERNIGHT. 


&&

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

&&

$$

PUBLIC...MW
AVIATION...SMITH
SYNOPSIS...MW

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