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 WWW.WEATHER.GOV/LOSANGELES