430 FXUS66 KLOX 212035 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 130 PM PDT FRI AUG 21 2015 .SYNOPSIS... HIGH PRESSURE WILL LOCK INTO THE FOUR CORNERS REGION SUNDAY THROUGH NEXT FRIDAY. AS RESULT MORNING CLOUDS WILL BECOME CONFINED TO THE COASTAL PLAIN WITH A GRADUAL WARMING TREND INTO EARLY NEXT WEEK. LITTLE CHANGE IS EXPECTED IN THE APPARENT WEATHER NEXT WEEK WITH TEMPERATURES REMAINING ABOVE NORMAL. && .SHORT TERM (TODAY-MON)... A WEAK UPPER-LEVEL RIDGE REMAINS IN PLACE THIS AFTERNOON WITH A WEAK UPPER LOW ABOUT 850 MILES OFF THE COAST. LOW CLOUDS HAVE BEEN STUBBORN TO CLEAR OUT OF THE LA/VENTURA/SBA COASTAL AND VALLEY AREAS THIS AFTERNOON...BUT SATELLITE IMAGERY INDICATES THAT THE STRATUS IS STARTING TO DISSIPATE. AS A RESULT OF THE SLOWER CLEARING... TEMPERATURES ARE RUNNING SEVERAL DEGREES COOLER THAN THIS TIME YESTERDAY...BUT STILL THINK THAT WE WILL GET CLOSE TO YESTERDAY'S HIGHS AND TODAY'S FORECAST HIGHS IN MOST PLACES. THE UPPER-LEVEL RIDGE WILL BUILD THROUGH EARLY NEXT WEEK...WITH THE RIDGE AXIS SHIFTING OVER THE AZ/NM BORDER BY MONDAY. THE WEAK CUTOFF LOW WILL GET ABOSORBED INTO A DEVELOPING LONG-WAVE TROUGH WELL OFF THE COAST DURING THIS TIME. AT THE SURFACE...THE ONSHORE PRESSURE GRADIENTS WILL WEAKEN THROUGH MONDAY AS WELL. THE ABOVE SYNOPTIC CHANGES WILL RESULT IN A WARMING TREND OVER THE WEEKEND INTO EARLY NEXT WEEK... ALONG WITH A SHRINKING MARINE LAYER. THE NAM SUGGESTS THAT BY SUNDAY MORNING...THE MARINE LAYER DEPTH WILL BE ABOUT HALF OF ITS CURRENT DEPTH. THIS WOULD BRING THE MARINE LAYER DEPTH TO ABOUT 1000-1500 FEET BY SUNDAY MORNING. BY MONDAY MORNING THERE IS A GOOD CHANCE THAT LOW CLOUDS AND FOG WILL BE CONFINED TO JUST THE COASTAL AREAS. HIGHS IN THE VALLEYS ON MONDAY WILL BE AROUND 100 DEGREES FOR THE WARMER VALLEY AREAS...WITH UPPER 70S AND 80S FOR THE COAST. THESE TEMPERATURES ARE ABOUT 5-10 DEGREES ABOVE NORMAL FOR THE VALLEY AREAS AND SEVERAL DEGREES ABOVE NORMAL FOR THE COASTAL AREAS. .LONG TERM (TUE-FRI)... LONG-RANGE MODELS ARE IN GOOD AGREEMENT THAT HEIGHT AND THICKNESS VALUES WILL CONTINUE TO RISE THROUGH AT LEAST MID-WEEK AS A VERY LARGE UPPER-LEVEL RIDGE DEVELOPS OVER THE WESTERN U.S. HOWEVER...IT APPEARS THAT AN EQUALLY STRONG TROUGH OFF THE PACIFIC NORTHWEST WILL PREVENT THE UPPER-HIGH FROM EXPANDING WEST AND RESULTING IN AN EXTREME HEAT WAVE FOR SW CALIFORNIA. REGARDLESS...SLIGHT WARMING SHOULD CONTINUE THROUGH AT LEAST MID-WEEK...WITH SLIGHTLY ABOVE NORMAL OR ABOVE NORMAL TEMPERATURES IN MOST PLACES. THE MARINE LAYER WILL CONTINUE TO SHRINK THROUGH MID-WEEK AS WELL...WITH A CHANCE THAT MANY COASTAL AREAS WILL BE FREE OF LOW CLOUDS BY TUESDAY OR WEDNESDAY. THE MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT THROUGH THURSDAY...THEN START TO DIVERGE ON FRIDAY...WHEN THE ECMWF TRIES TO PUSH A TROUGH THROUGH NORTHERN CALIFORNIA...WHILE THE GFS KEEPS THE UPPER-LOW WELL OFF THE COAST WITH A WEAK RIDGE OVER THE WEST COAST. FOR NOW...WENT WITH SLIGHT COOLING FOR LATE NEXT WEEK AS THE GFS ENSEMBLE MEAN KEEPS THE UPPER-LEVEL TROUGH CLOSER TO THE COAST. && .AVIATION...21/18Z AT 17Z AT KLAX... THE INVERSION WAS 2200 FEET DEEP. THE TOP WAS NEAR 5450 FEET WITH A TEMPERATURE OF 25 DEGREES CELSIUS. OVERALL... MODERATE CONFIDENCE IN THE 18Z TAFS FOR THE COASTAL AND ADJACENT VALLEYS LOCATIONS AND HIGH ELSEWHERE. THE MARINE INTRUSION IS A BIT DEEPER THIS MORNING AND COMBINED WITH A MINOR CATALINA EDDY THIS WILL MAKE CLEARING A BIT SLUGGISH IN ALL COASTAL AND ADJACENT VALLEY AREAS BUT IN PARTICULAR IN THE INTERIOR LOCATIONS HOWEVER SKIES WILL CLEAR BY MIDDAY. THE INTRUSION WILL BE SLOWER TO REDEVELOP EACH NIGHT AND SHOULD DIMINISH MORE QUICKLY EACH MORNING THROUGH THE WEEKEND. AT KSBP THE SMOKE WILL CONTINUE TO AFFECT VISIBILITIES INTO THE WEEKEND. OTHERWISE AND ELSEWHERE VFR CONDITIONS WILL PREVAIL. KLAX... MODERATE CONFIDENCE IN THE 18Z TAF. THE MARINE INTRUSION IS A BIT DEEPER THIS MORNING AND COMBINED WITH A MINOR CATALINA EDDY THIS WILL MAKE CLEARING A BIT SLUGGISH HOWEVER SKIES WILL CLEAR BY MIDDAY. THE INTRUSION WILL BE SLOWER TO REDEVELOP EACH NIGHT AND SHOULD DIMINISH MORE QUICKLY EACH MORNING THROUGH THE WEEKEND. OTHERWISE VFR CONDITIONS WILL PREVAIL. KBUR... MODERATE CONFIDENCE IN THE 18Z TAF. THE MARINE INTRUSION IS A BIT DEEPER THIS MORNING AND COMBINED WITH A MINOR CATALINA EDDY THIS WILL MAKE CLEARING A BIT SLUGGISH HOWEVER SKIES WILL CLEAR BY MIDDAY. THE INTRUSION WILL BE SLOWER TO REDEVELOP EACH NIGHT AND SHOULD DIMINISH MORE QUICKLY EACH MORNING THROUGH THE WEEKEND. OTHERWISE VFR CONDITIONS WILL PREVAIL. && .MARINE...21/130 PM. LOCALLY MODERATE NORTHWEST WINDS WILL FLOW ACROSS THE CENTRAL AND SOUTHERN PORTIONS OF THE OUTER WATERS AND THE WESTERN PORTION OF THE SANTA BARBARA CHANNEL THROUGH LATE TONIGHT. WIND SPEEDS IN THIS AREA WILL BE ELEVATED WITH OCCASIONAL GUSTS TO 25 KT BUT IN GENERAL THEY WILL ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA. THERE IS A TWENTY FIVE PERCENT CHANCE OF AN ADVISORY BEING NEEDED THIS EVENING. OTHERWISE AND ELSEWHERE CONDITIONS FOR THE COASTAL WATERS WILL BE BELOW ADVISORY LEVELS. && .FIRE WEATHER...21/1625Z ELEVATED FIRE DANGER THROUGH THE WEEKEND FOR THE ANTELOPE VALLEY... MOUNTAINS... AND INTERIOR VALLEYS DUE TO COMBINATION OF GUSTY ONSHORE WINDS...WARM TEMPERATURES...AND LOW HUMIDITIES. AN UNUSUALLY STRONG ONSHORE FLOW FOR AUGUST COMBINED WITH A RATHER DEEP MARINE LAYER PATTERN WILL KEEP TEMPERATURES BELOW NORMAL AND HIGHER HUMIDITIES FOR MOST COASTAL AND VALLEY AREAS THROUGH SATURDAY. INTERIOR SECTIONS AWAY FROM THE MARINE LAYER WILL REMAIN VERY WARM AND DRY THROUGH THE PERIOD. THE ANTELOPE VALLEY... MOUNTAINS...AND INTERIOR VALLEYS WILL GENERALLY SEE HUMIDITY READINGS BETWEEN 10 AND 20 PERCENT THOUGH THE WEEK...WITH ISOLATED SINGLE DIGIT READINGS. THE STRONG ONSHORE FLOW PATTERN WILL MAINTAIN GUSTY ONSHORE WINDS EACH AFTERNOON AND EVENING THROUGH SATURDAY ACROSS INTERIOR SECTIONS...WHERE GUSTS BETWEEN 25 AND 40 MPH WILL BE COMMON. ISOLATED GUSTS AS HIGH AS 45 MPH CAN BE EXPECTED THIS AFTERNOON ACROSS THE FOOTHILLS OF THE ANTELOPE VALLEY. BRIEF CRITICAL FIRE WEATHER CONDITIONS POSSIBLE EACH AFTERNOON THROUGH SATURDAY. && .LOX WATCHES/WARNINGS/ADVISORIES... NONE && $$ PUBLIC...SUKUP AVIATION/MARINE...KJ FIRE WEATHER...GOMBERG SYNOPSIS...MUNROE WWW.WEATHER.GOV/LOSANGELES