Weather Service Report


207 
FXUS66 KLOX 191738 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1040 AM PDT FRI SEP 19 2014

.SYNOPSIS...
WEAK UPPER LEVEL LOW PRESSURE WILL BRING BELOW NORMAL TEMPERATURES 
TO MUCH OF THE REGION THROUGH THE WEEKEND. TEMPERATURES WILL LIKELY 
WARM TO NEAR NORMAL EARLY NEXT WEEK AS THE UPPER LOW MOVES EAST AND 
HIGH PRESSURE BRIEFLY RETURNS. ANOTHER TROUGH OF LOW PRESSURE MAY 
BRING A COOLING TREND FOR THE SECOND HALF OF NEXT WEEK.
 
&&

.SHORT TERM (REST OF TODAY-SUN)...WITH THE CLOSED UPPER LOW 
CONTINUING TO SPIN ITS WAY DOWN THE CENTRAL COAST...A WEAK ONSHORE 
GRADIENT AND A MODERATE TO STRONG EDDY...THERE'S BEEN QUITE A BIT OF 
STRATUS COVERAGE INLAND THIS MORNING WITH AROUND A 3K FT MARINE 
LAYER. COOLING TREND ALSO ON TRACK WITH MANY LOCATIONS AS MUCH AS 10 
DEG COOLER THAN YESTERDAY MORNING'S READINGS AT THIS TIME. SO COOLER 
HIGH TEMPS FORECAST FOR TODAY LOOK GOOD. VISIBLE LOOP SHOWING 
STRATUS DECK IS TRYING TO THIN OUT SO EXPECT MOST AREAS TO CLEAR OUT 
BY LATE MORNING BUT POSSIBLY NOT BY EARLY AFTERNOON. WILL TWEAK THE 
FORECAST FOR LESS CLOUDS THIS AFTERNOON OVER ALL BUT THE VENTURA AND 
SBA COUNTY MOUNTAINS WHERE THERE STILL APPEARS TO BE AT LEAST A 
SLIGHT CHANCE OF CONVECTION THIS AFTERNOON. LATEST MODEL CONVECTIVE 
PARAMETERS SHOW SOME INSTABILITY WITH LIFTED INDICIES AROUND -3.0 
CENTERED OVER THE VTU COUNTY MOUNTAINS NORTH INTO SBA MOUNTAINS...A 
POOL OF LOW TO MID LEVEL MOISTURE INDICATED BY A BROAD AREA OF 850 
DEWPOINTS BETWEEN 10 AND 12C...AND FINALLY SOME DYNAMIC HELP FROM A 
FAVORABLE POSITION OF THE UPPER LOW. WHAT DOES FORM SHOULD BE MOVING 
FAST ENOUGH TO LIMIT ANY FLASH FLOODING. OVERALL WILL LEAVE TRW 
CHANCES IN THE FORECAST FOR THIS AFTERNOON OVER THE AREAS OF VTU AND 
SBA COUNTY MOUNTAINS. CONVECTIVE INDICATORS HINT AT POSSIBLE 
ACTIVITY OVER THE LA COUNTY MOUNTAINS BUT WILL KEEP CHANCES OUT FOR 
NOW AND MONITOR THROUGH THE AFTERNOON. 

WILL LIKELY GO AHEAD AND ADD TRW CHANCES FOR SATURDAY AFTERNOON IN 
THIS AFTERNOON'S UPDATE. MOISTURE APPEARS TO BE A LITTLE MORE 
LIMITED...BUT MODELS FORECASTING THE UPPER LOW TO EJECT OUT OVER THE 
AREA TOMORROW...SO MOISTURE DEFICIENCY SHOULD BE MADE UP FOR BY 
BETTER DYNAMICS. AT FIRST GLANCE BELIEVE BETTER CHANCE WILL AGAIN BE 
OVER VTU AND SBA COUNTY MOUNTAINS DUE TO THAT AREA'S RELATIVELY 
BETTER MOISTURE AVAILABILITY...BUT DYNAMICS APPEAR BETTER SOUTH OVER 
LA COUNTY. WILL TAKE A CLOSER LOOK THIS AFTERNOON. THE MORNING'S 
MARINE LAYER STRATUS WILL BE A TRICKY FORECAST SO PERSISTENCE LOOKS 
TO BE THE BEST OPTION.  

***FROM PREVIOUS DISCUSSION***    

LATEST FOG PRODUCT IMAGERY INDICATED PLENTY OF LOW LEVEL MOISTURE 
LINGERING ACROSS COAST AND VALLEYS N OF POINT CONCEPTION...WHILE LOW 
CLOUDS WERE MORE RANDOM IN NATURE FOR AREAS SOUTH OF POINT 
CONCEPTION. LOW CLOUDS SHOULD FILL IN ACROSS COAST AND VALLEYS OF 
LOS ANGELES...VENTURA AND SANTA BARBARA COUNTIES BY DAWN. THERE WILL 
BE ENOUGH LOW LEVEL LIFT TO CAUSE SOME PATCHY DRIZZLE TO OCCUR JUST 
ABOUT ANYWHERE WEST OF THE MOUNTAINS THIS MORNING. LATEST ACARS 
SOUNDING NEAR LAX SHOWED A VERY WEAK INVERSION IN PLACE WHICH MAKES 
SENSE WHY CLOUDS ARE NOT MORE UNIFORM S OF POINT CONCEPTION THIS 
MORNING. WIND PATTERNS ARE INTERESTING THIS MORNING. OVER THE 
COASTAL AREAS INTO LA COUNTY THE FLOW IS MOSTLY CYCLONIC NW BECOMING 
SW OVER LA COUNTY. HOWEVER...NORTHERLY WINDS WERE OCCURRING OVER THE 
MOUNTAINS AND SAN JOAQUIN VALLEY. THIS NORTHERLY FLOW WAS CAUSING 
ADDITIONAL CLOUDS TO PILE UP ALONG THE NORTHERN SLOPES OF THE LOCAL 
MOUNTAINS THIS MORNING INCLUDING THE I-5 CORRIDOR.

SYNOPTICALLY...A CLOSED 578 DM UPPER LOW CURRENTLY OFF THE CENTRAL 
COAST WILL DRIFT SLOWLY SOUTH JUST WEST OF POINT CONCEPTION BY THIS 
AFTERNOON. THE PROXIMITY OF THE UPPER LOW WILL ALLOW FAVORABLE COOL 
CYCLONIC FLOW OVER MOST OF LOS ANGELES...VENTURA AND SANTA BARBARA 
COUNTIES TODAY. THERE IS NOT MUCH IN THE WAY OF MOISTURE ASSOCIATED 
WITH THE UPPER LOW...BUT THERE WILL BE PLENTY LOW CLOUDS LINGERING 
ACROSS THE COAST AND VALLEYS THROUGH THIS MORNING AND INTO THE 
AFTERNOON ACROSS MOST COASTAL AREAS. RAP AND NAM-WRF MODELS 
INDICATED THAT THERE WOULD BE ENOUGH INSTABILITY AND LIMITED MID 
LEVEL MOISTURE TO WARRANT A SLIGHT CHANCE FOR SHOWERS OR 
THUNDERSTORMS TO DEVELOP OVER THE VENTURA COUNTY MOUNTAINS AS WELL 
AS PORTIONS OF THE SANTA BARBARA COUNTY MOUNTAINS THIS AFTERNOON AND 
EVENING HOURS. TEMPERATURES WILL CONTINUE TO TREND COOLER THROUGH 
SATURDAY AS THE UPPER LOW MOVES DIRECTLY OVER SBA/VENTURA 
COUNTIES SATURDAY AFTERNOON. THERE IS NOT MUCH DIFFLUENCE ASSOCIATED 
WITH THE UPPER LOW FOR SATURDAY AND MODELS WERE NOT PICKING UP ON 
ANY ADDITIONAL MOISTURE OR CONVECTIVE PARAMETERS ACROSS THE LOCAL 
MOUNTAINS. WILL LET LATER SHIFTS LOOK CLOSER TO SEE IF SLIGHT CHANCE 
POPS WILL BE NEEDED FOR SAT IN THE LOCAL MTNS ONCE AGAIN.EXPECT HIGH 
TEMPS TO BE NEAR OR JUST BELOW NORMAL TODAY AND SATURDAY.

BY SUNDAY...THE UPPER LOW WILL FILL IN AND MOVE NE INTO NEVADA 
ALLOWING HEIGHTS AND THICKNESS LVLS TO RISE. THERE WILL BE NIGHT 
THROUGH MORNING LOW CLOUDS BUT A QUICKER BURNOFF AND HIGH TEMPS WILL 
BE A FEW DEGREES HIGHER...ESPECIALLY ACROSS INTERIOR 
LOCATIONS...WITH WARMEST VALLEY LOCATIONS IN THE MID 80S...AND MID 
TO UPPER 70S ALONG THE COAST. 


.LONG TERM (MON-THU)...BOTH GFS AND ECMWF STAY IN PRETTY GOOD 
AGREEMENT OVER THE LONG TERM PERIOD. A WEAK RIDGE WILL BEGIN TO 
BUILD OVER BAJA CALIFORNIA WHILE MUCH OF NORTHERN CALIFORNIA REMAIN 
UNDER A BROAD UPPER TROUGH THROUGH WED. EXPECT NIGHT THROUGH MORNING 
LOW CLOUDS FOR COASTAL AREAS AND POSSIBLY SOME COASTAL VALLEYS 
THROUGH WED MORNING. TEMPS WILL CONTINUE TO REBOUND MONDAY AND 
TUESDAY WITH HIGHS REACHING THE LOWER 90S ACROSS WARMEST VALLEY 
LOCATIONS. FOR WED AND THU...A BROAD UPPER TROUGH WILL BEGIN TO DIG 
FARTHER SOUTH. THE GFS IS SHOWING A SHARPER TROUGH WHICH WOULD MEAN 
MORE SIGNIFICANT COOLING BY THURSDAY...WHERE THE EUROPEAN MODEL IS 
LESS PRONOUNCED. AT THIS POINT HAVE TRENDED HIGH TEMPS DOWN SLIGHTLY 
FOR WED...WITH A FEW MORE DEGREES OF COOLING FOR THURSDAY TO 
SLIGHTLY BELOW NORMAL FOR THIS TIME OF YEAR. 


&&

.AVIATION...19/1800Z.

MID/UPPER LEVEL LOW PRESSURE SYSTEM CENTERED SOUTHWEST OF POINT 
CONCEPTION WILL SHIFT NORTHEAST. UPPER LEVEL STRONG SOUTHWEST WINDS 
WILL BECOME MODERATE SOUTHWEST BY 21/00Z WHILE MID LEVEL LIGHT 
SOUTHEAST WINDS BECOME MODERATE SOUTHEAST AFTER 20/08Z OVER THE 
AREA. ISOLATED THUNDERSTORMS BETWEEN 19/23-20/03Z OVER VENTURA AND 
SANTA BARBARA COUNTY MOUNTAINS WITH TOPS 45KFT AND STORMS WILL MOVE 
NORTH APPROXIMATELY 15KT. LOW LEVEL CLOUD TOPS WERE APPROXIMATELY 
3KFT ALONG THE CENTRAL COAST TO 3KFT OVER THE BIGHT. THE CAPPING 
INVERSION WAS WEAK AND WILL LIKELY DIFFER LITTLE SATURDAY MORNING 
FROM THIS MORNING. THE CLOUD FIELD WAS DISORGANIZED...BROKEN OVER 
THE BIGHT AND SCATTERED ON THE CENTRAL COAST AND WILL LIKELY 
CONTINUE DISORGANIZED SATURDAY MORNING. WEAK ONSHORE PRESSURE 
GRADIENT BECOMING MODERATE ONSHORE AFTER 20/19Z.  

KLAX...LIKELY SCATTERED 035 BY 19/20Z. CHANCE CIGS 015 BETWEEN 
20/09-20/17Z AND CIGS 027 BETWEEN 20/17-20/19Z.

KBUR...LIKELY SCATTERED 025 BY 19/20Z. CHANCE CIGS 017 BY 20/10Z. 

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

&&

.MARINE...19/900 AM.
THERE IS A CHANCE SMALL CRAFT ADVISORY CONDITIONS IN THE VICINITY OF 
THE NORTHERN CHANNEL ISLANDS WILL DEVELOP THIS AFTERNOON AND END 
LATE TONIGHT. THERE IS A CHANCE SMALL CRAFT ADVISORY CONDITIONS WILL 
REDEVELOP EACH EVENING AND EXIST SEVERAL HOURS EACH DAY 
SUNDAY THROUGH TUESDAY. THERE IS A CHANCE THE NORTHWEST WINDS WILL 
INCREASE TO GALES THURSDAY AFTERNOON IN THE VICINITY OF THE NORTHERN 
ISLANDS TO SAN NICOLAS ISLAND. A MIXED WEST NORTHWEST SWELL AND 
SOUTH SOUTHWEST SWELL WILL CONTINUE TO SUBSIDE AND LINGER THROUGH 
SATURDAY. SWELLS ORIGINATING FROM A FAST MOVING AND SHORT LIVED GULF 
OF ALASKA STORM ON THURSDAY ARE EXPECTED TO ARRIVE SUNDAY FROM 
295-305. THERE IS A CHANCE THE SWELL WILL PEAK SUNDAY NIGHT AND 
LINGER THROUGH TUESDAY. A LOW PRESSURE SYSTEM IS LIKELY TO DEVELOP 
OVER THE EASTERN PACIFIC NEXT WEEK MONDAY THROUGH TUESDAY AND 
GUIDANCE HAD TRENDED DEEPER WITH THE SYSTEM. SWELLS GENERATED BY 
STORM FORCE WINDS ARE EXPECTED TO ARRIVE FROM 300-310 DEGREES 
WEDNESDAY EVENING AND PEAK THURSDAY AND LINGER THROUGH FRIDAY. 

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).

&&

$$

PUBLIC...JACKSON/KAPLAN
AVIATION/MARINE...30
SYNOPSIS...SUKUP

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