359 
FXUS66 KLOX 292052
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
150 PM PDT SAT SEP 29 2012

.SYNOPSIS...

AS HIGH PRESSURE BUILDS OVER THE GREAT BASIN..TEMPERATURES WILL WARM 
TO ABOVE NORMAL THROUGH THE MIDDLE OF NEXT WEEK...WITH RECORD 
BREAKING HEAT POSSIBLE ON MONDAY AND TUESDAY FOR SOME LOCATIONS. 
ONSHORE FLOW WILL RETURN LATE TUESDAY AND WEDNESDAY WITH A COOLING 
TREND EXPECTED FOR THE REST OF NEXT WEEK.
 
&&

.SHORT TERM (TONIGHT-TUE)...
MAIN FORECAST ISSUE WILL BE TEMPERATURES THROUGH TUESDAY. MARINE 
LAYER CONTINUES TO SHRINK TO JUST A FEW HUNDRED FEET THIS 
AFTERNOON...HOWEVER LOW CLOUDS PERSIST ALONG THE CENTRAL COAST 
BEACHES. EXPECT STRATUS AND FOG IN THESE AREAS TONIGHT BUT QUICKLY 
DISSIPATING EARLY SUNDAY. A FEW HIGH CLOUDS CONTINUE TO STREAM 
ACROSS SOUTHERN COUNTIES AND A FEW CUMULUS BUILD-UPS OCCURRING IN 
THE MOUNTAINS DUE TO LEFTOVER MOISTURE. ONLY SIGNIFICANT WEATHER 
FEATURE TONIGHT IS A WEAK SUNDOWNER FOR THE SANTA YNEZ MOUNTAINS. 
EXPECT UP TO 20KT NORTHERLY WINDS TO CREATE SOME GUSTY WINDS THROUGH 
AND BELOW PASSES AND CANYONS OF SANTA BARBARA COUNTY...BUT REMAIN 
BELOW ADVISORY LEVEL.

THE UPPER LOW PRESSURE SYSTEM WELL OFF THE WEST COAST WOBBLES BACK 
TO THE WEST ON SUNDAY. THIS ALLOWS HIGH PRESSURE TO BUILD ACROSS 
CALIF WITH THE OFFSHORE PRESSURE GRADIENTS BRINGING DRIER AIR ACROSS 
THE REGION. MAXIMUM TEMPERATURES WILL INCREASE 3-6 DEGREES FOR MOST 
VALLEY AND COASTAL AREAS ON SUNDAY. THE HOTTEST AND DRIEST DAY WILL 
BE MONDAY WITH SLIGHTLY STRONGER OFFSHORE TRENDS. ALL TEMP STUDY 
DATA AND CURRENT BIAS-CORRECTED MODEL GUIDANCE ARE SLIGHTLY COOLER 
THAN PREVIOUS FORECASTS...SO HAVE REDUCED HIGHS BY A DEGREE OR TWO. 
THIS STILL WILL CREATE NEAR RECORD HIGH TEMPERATURES FOR MONDAY 
AFTERNOON WITH HUMIDITIES IN THE SINGLE DIGITS...MAKING IT FEEL LESS 
HOT OVERALL. THE MAIN FORECAST CHANGE OCCURS ON TUESDAY. 950MB TEMPS 
COOL BY 6-8 DEGREES CELSIUS OVER NORTHERN COUNTIES AND 2-5 DEGREES 
OVER VENTURA AND LOS ANGELES COUNTIES...PLUS WINDS TURN ONSHORE IN 
THE AFTERNOON. HAVE REDUCED MAXIMUM TEMP FORECASTS BY 3-6 DEGREES 
FOR TUESDAY OVER WHAT WE EXPECT ON MONDAY. THIS ONSHORE FLOW 
TRANSITION WILL MAKE IT DIFFICULT TO REACH MAX HEATING ALONG COASTAL 
AREAS DEPENDING ON WHEN THE MARINE AIR KICKS IN. THIS WILL ALSO BE A 
CRITICAL FIRE WEATHER PERIOD ON TUESDAY WHEN ONSHORE WINDS COMBINE 
WITH HOT INLAND TEMPERATURES. SEE FIRE DISCUSSION BELOW. OTHER 
ADJUSTMENTS INCLUDED HIGHER NIGHTTIME TEMPERATURES FOR THE SANTA 
MONICA AND SAN GABRIEL MOUNTAIN FOOTHILL AREAS WHERE READINGS WILL 
LIKELY REMAIN IN THE 70S AND LOWER 80S SUNDAY AND MONDAY NIGHTS.

.LONG TERM (WED-SAT)...
THE HIGH PRESSURE RIDGE WILL BE FURTHER MODIFIED ON WEDNESDAY AS THE 
UPPER LOW PRESSURE SYSTEM OFF THE COAST SHIFTS NORTHWARD AND THE 
FIRST WINTER STORM SYSTEM OF THE SEASON ENTERS THE NORTHERN ROCKIES. 
OUR HEIGHTS SLOWLY DROP ON WEDNESDAY WITH A STRONGER ONSHORE FLOW 
WHICH WILL KNOCK ANOTHER 4-8 DEGREES OFF THE AFTERNOON HIGHS. THIS 
COOLING TREND CONTINUES ALL WEEK WITH A DEEPENING MARINE LAYER 
LEADING TO HIGHER INLAND HUMIDITIES AND MORNING/NIGHT COASTAL CLOUDS 
AND FOG. EXPECT A LOW PRESSURE SYSTEM TO BE PARKED OFF THE NORTHERN 
CALIF COAST BY SATURDAY. 

&&

.AVIATION...29/1800Z.

MID/UPPER LEVEL TROUGH OF LOW PRESSURE UPSTREAM WILL SHIFT NORTH AND 
WEST WHILE A RIDGE OF HIGH PRESSURE CENTERED SOUTH APPROACHES THE 
AREA. UPPER LEVEL MODERATE TO STRONG SOUTHWEST WINDS WILL BECOME 
WEST SOUTHWEST WHILE MID LEVEL LIGHT NORTH WINDS BECOME EAST THEN 
SOUTHEAST AFTER 30/15Z. MARINE LAYER TOP WAS .8KFT THIS MORNING AND 
WILL DIFFER BY MINUS .6KFT...LOW CLOUD FIELD WILL DISSIPATE AND OR 
SHIFT OFFSHORE. WEAK TO MODERATE ONSHORE PRESSURE GRADIENT THROUGH 
30/01Z AND AFTER 30/21Z OTHERWISE WEAK TO MODERATE NORTHERLY 
GRADIENT BETWEEN 30/05-30/18Z.

KLAX...VERY LIKELY SCT 250 AFTER 30/03Z. CHANCE LOW LEVEL WINDS 
08010KT AT APPROXIMATELY 1KFT BETWEEN 30/07-30/12Z.   

KBUR...VERY LIKELY SCT AFTER 30/03Z. CHANCE LOW LEVEL WINDS 01010KT 
AT APPROXIMATELY 2KFT BETWEEN 30/05-30/11Z. 

VIRTUALLY CERTAIN - 95-100%
VERY LIKELY       - 80-95%
LIKELY            - 60-80%
CHANCE            - 30-60%
VERY UNLIKELY     - 20% OR LESS

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING (SEE LAXRFWLOX).
FIRE WEATHER WATCH (SEE LAXRFWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
HIGH RIP CURRENT RISK (SEE LAXSRFLOX).
SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).

&&

$$

PUBLIC...BOLDT
AVIATION...30
SYNOPSIS...BARTLING

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