Weather Service Report


595 
FXUS66 KLOX 211606
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
900 AM PDT THU AUG 21 2014

.SYNOPSIS...
SOME LINGERING MID-LEVEL MOISTURE WILL RESULT IN A SLIGHT CHANCE OF 
MOUNTAIN AND DESERT THUNDERSTORMS THIS AFTERNOON. OTHERWISE...EXPECT 
A SLIGHT COOLING TREND THROUGH SATURDAY WITH INCREASING COASTAL LOW 
CLOUDS AND FOG FOLLOWED BY A WEAK AND GRADUAL WARMING TREND NEXT 
WEEK. 

&&

.SHORT TERM (TODAY-SAT)...
*** MID MORNING DISCUSSION UPDATE ***
MUCH QUIETER THIS MORNING ACROSS THE REGION.  A FEW THUNDERSTORMS 
WITH ACTIVE CLOUD TO GROUND LIGHTNING ARE ALONG THE 
CALIFORNIA-ARIZONA BORDER BUT ARE EXITING TO THE EAST AND WILL NOT 
AFFECT THE LOX SERVICE AREA.  THE MARINE LAYER WAS NOT AS WIDESPREAD 
THIS MORNING AND TEMPERATURES IN MANY INLAND VALLEYS ARE ALREADY A 
FEW DEGREES WARMER THAN YESTERDAY DUE TO THE EARLIER ACCESS TO SOLAR 
HEATING.

THE PRIMARY QUESTION AGAIN TODAY CONCERNS THE CHANCE OF 
THUNDERSTORMS.  THE CURRENT FORECAST PACKAGE HAS A SLIGHT CHANCE OF 
THUNDERSTORMS IN THE VENTURA AND LOS ANGELES COUNTY MOUNTAINS AS 
WELL AS IN THE ANTELOPE VALLEY.  THOUGH THE INSTABILITY REMAINS 
PRETTY GOOD IN THESE AREAS TODAY THE ACCESS TO PRECIPITABLE WATER 
REMAINS LOW... IS LOWER THAN IN THE AREA YESTERDAY... AND IS EVEN 
LOWER THAN THE PROJECT FOR TODAY.  AM LIKELY TO REMOVE THE 
THUNDERSTORM CHANCES FROM THE FORECAST PACKAGE FOR TODAY BUT WILL 
WAIT TO SEE IF WE POP ANY CU OVER THE MOUNTAINS BY MIDDAY AND TAKE A 
LOOK AT THE NEXT ROUND OF GUIDANCE.

NO OTHER NOTABLE CHANGES ARE EXPECTED TO THE FORECAST PACKAGE.

*** EARLY MORNING DISCUSSION***
OVERALL...00Z MODELS IN GOOD SYNOPTIC AGREEMENT THROUGH THE PERIOD. 
AT UPPER LEVELS...LOW PRESSURE SYSTEM WILL CONTINUE TO MOVE EASTWARD 
ACROSS FAR SOUTHERN CALIFORNIA TODAY AND INTO THE 4-CORNERS AREA 
TONIGHT...WITH WEAK CYCLONIC FLOW REMAINING OVER THE AREA 
FRIDAY/SATURDAY. NEAR THE SURFACE...A MODERATE ONSHORE FLOW WILL 
CONTINUE...STRENGTHENING A BIT BY FRIDAY/SATURDAY.

FORECAST-WISE...THE OVERALL WEATHER PATTERN SHOULD BE RATHER 
UNREMARKABLE. MODELS INDICATE SOME REMNANT MID-LEVEL MOISTURE AND 
INSTABILITY OVER THE VENTURA/LA MOUNTAINS AND ANTELOPE VALLEY THIS 
AFTERNOON/EVENING. SO...AN ISOLATED SHOWER/TSTM CANNOT BE RULED OUT 
SO WILL CONTINUE WITH SLIGHT CHANCE POPS FOR THOSE AREAS WITH THE 
MORNING FORECAST.

OTHERWISE...THE PATTERN THROUGH SATURDAY WILL BE DICTATED BY THE 
INFLUENCE OF THE MARINE LAYER STRATUS. STRATUS HAVING A HARD TIME 
GETTING ESTABLISHED THIS MORNING...AND SKIES COULD START OUT A LOT 
MORE SUNNY ACROSS COASTAL/VALLEY AREAS THAN PREVIOUSLY EXPECTED. FOR
TONIGHT THROUGH SATURDAY...THE CONTINUED ONSHORE FLOW SHOULD HELP 
GET THE MARINE STRATUS ESTABLISHED ACROSS THE COASTAL PLAIN AND 
LOCALLY INTO THE COASTAL VALLEYS (ESPECIALLY BY SATURDAY MORNING). 
WITH THE INVERSION REMAINING ON THE WEAK SIDE...ANY STRATUS THAT 
DEVELOPS DURING THE NIGHT/MORNING HOURS SHOULD DISSIPATE NICELY EACH 
AFTERNOON. 

AS FOR TEMPERATURES...EXPECT ONLY MINOR FLUCTUATIONS FROM TODAY 
THROUGH SATURDAY. FOR COASTAL/VALLEY AREAS...TODAY SHOULD BE A FEW 
DEGREES WARMER DUE TO LESS MARINE LAYER INFLUENCE...BUT A SLIGHT 
COOLING TREND IS ANTICIPATED FRIDAY/SATURDAY DUE TO ANTICIPATED 
INCREASE IN STRATUS COVERAGE. FOR INLAND AREAS...TODAY SHOULD BE 
SEVERAL DEGREES WARMER...WITH NEAR PERSISTENCE/VERY SLIGHT COOLING 
FOR FRIDAY/SATURDAY.

.LONG TERM (SUN-WED)...FOR EXTENDED...MODELS SHOW SOME SIGNIFICANT 
DIFFERENCES WHICH RESULT IN A RATHER LOW CONFIDENCE FORECAST. AT
UPPER LEVELS...BOTH THE GFS/ECMWF NOSE IN A RIDGE FROM THE SOUTHEAST 
ON SUNDAY. HOWEVER...FROM MONDAY THROUGH WEDNESDAY...THE MODELS 
DIVERGE NOTICEABLY. THE GFS MAINTAINS ITS PREVIOUS THINKING OF A 
EASTERN PACIFIC RIDGE SHIFTING EASTWARD OVER THE DISTRICT. THE ECMWF 
ON THE OTHER HAND DROPS A LOW PRESSURE SYSTEM SOUTH ACROSS 
CALIFORNIA. THIS NEW ECMWF SOLUTION IS VASTLY DIFFERENT FROM THE 12Z 
RUN (WHICH MATCHED UP WELL WITH THE CONSISTENT GFS SOLUTIONS). SO 
WILL DISCOUNT THIS NEW ECMWF SOLUTION FOR NOW. 

FORECAST-WISE...THE IDEA OF A BUILDING UPPER LEVEL RIDGE WILL MEAN A 
WARMING TREND FOR ALL AREAS THROUGH THE PERIOD. AS FOR SKY 
CONDITION...WILL EXPECT GENERALLY MOSTLY CLEAR SKIES WITH ANY 
STRATUS/FOG LIKELY CONFINED TO THE COASTAL PLAIN. THERE COULD BE 
SOME INCREASE IN MID/HIGH LEVEL CLOUDS EARLY NEXT WEEK FROM THE 
VARIOUS TROPICAL SYSTEMS IN THE EASTERN PACIFIC...BUT NOT CONFIDENT 
ENOUGH IN ANY MODEL SOLUTION TO INCLUDE ANY MENTION IN THE MORNING 
FORECAST PACKAGE AT THIS TIME. 

&&

.AVIATION...21/1240Z...

N OF POINT CONCEPTION...
LOW CONFIDENCE WITH 12Z TAFS. CIGS DID NOT MATERIALIZE THROUGH THE 
OVERNIGHT HOURS...BUT WERE APPROACHING THE CENTRAL COAST THIS 
MORNING. THERE IS A 30 PERCENT CHANCE THAT LIFR/IFR CIGS WILL AFFECT 
KSBP/KSMX THROUGH 16Z. LITTLE BETTER CONFIDENCE THAT LIFR CIGS WILL 
REDEVELOP AFTER 05-07Z TONIGHT. 20 PERCENT CHANCE THAT KPRB WILL GET 
IFR CIGS BETWEEN 14-16Z. 

S OF POINT CONCEPTION...MODERATE CONFIDENCE FOR SBA/VTU COUNTIES FOR 
VFR CONDS THIS MORNING. KLAX WILL EXPERIENCE MVFR CONDS THROUGH 16Z 
THIS MORNING...AND LONG BEACH SHOULD ALSO HAVE MVFR CIGS BY 14Z FOR 
A FEW HOURS. LOW CONFIDENCE FOR TIMING OF STRATUS TO REDEVELOP 
OVERNIGHT INTO FRIDAY MORNING. 40 PERCENT CHANCE THAT HIGH IFR OR 
LOW MVFR CIGS WILL DEVELOP +/- 2 HOURS FROM CURRENT TAF TIME. 

KLAX...MODERATE CONFIDENCE THAT MVFR CIGS WILL SCOUR OUT AT 16Z GIVE 
OR TAKE AN HOUR. LOWER CONFIDENCE FOR HIGH IFR/LOW MVFR CIGS TO 
REDEVELOP AT 08Z. CIGS COULD DELAY A FEW HOURS BEFORE DEVELOPING.

KBUR...HIGH CONFIDENCE WITH VFR CONDS. 20 PERCENT CHANCE FOR 
IFR/LIFR CONDS AFTER 11Z FRI MORNING. 

&&

.MARINE...21/900 AM...

NO SIGNIFICANT WIND ISSUES ANTICIPATED ACROSS THE COASTAL WATERS FOR 
THE NEXT SEVERAL DAYS.

THERE WILL BE AN INCREASING 4 TO 5 FT SOUTHERLY SWELL WITH A 
MODERATE PERIOD OF 12 SECONDS THANKS TO TROPICAL STORM LOWELL. AT 
THIS TIME IT LOOKS LIKE MODELS ARE INDICATING ANOTHER TROPICAL 
DISTURBANCE JUST WEST OF CENTRAL AMERICA TO STRENGTHEN AND POSSIBLY 
DEVELOP INTO A TROPICAL DEPRESSION...WITH FURTHER STRENGTHENING 
EXPECTED AS IT APPROACHES BAJA CALIFORNIA. A FEW LONG RANGE MODELS 
LOOK TO KEEP IT NEAR BAJA CALIFORNIA AS IT TRACKS TO THE NORTH. 
THERE COULD BE ANOTHER INCREASE TO THE SOUTHERLY SWELL WITH THIS 
NEXT SYSTEM BY EARLY NEXT WEEK. 

&&

.BEACH HAZARDS...21/230 AM...

A BEACH HAZARDS STATEMENT HAS BEEN ISSUED VALID FROM 9 AM TODAY 
THROUGH SUNDAY AFTERNOON. TROPICAL STORM LOWELL WILL BE SENDING A 4 
TO 5 FOOT SOUTHERLY SWELL WITH A MODERATE 12 SECOND PERIOD ACROSS 
THE COASTAL WATERS AFFECTING SOUTH FACING BEACHES WITH DANGEROUS RIP 
CURRENTS EXPECTED. THERE WILL BE ELEVATED SURF BY FRIDAY EVENING 
THROUGH SATURDAY EVENING WITH SETS 4 TO 7 FEET POSSIBLE. THERE WILL 
BE A CHANCE THAT THE BEACH HAZARDS STATEMENT MIGHT NEED TO BE 
UPGRADED TO A HIGH SURF ADVISORY BY SATURDAY MORNING IF SURF 
INCREASES SLIGHTLY WITH SETS TO 8 FEET. BEACHES MOST SUSCEPTIBLE 
TO DANGEROUS RIP CURRENTS WILL BE ZUMA...MALIBU...CABRILLO BEACHES 
AS WELL AS SOUTHERN VENTURA COUNTY BEACHES. STRONG RIP CURRENTS AND 
LONGSHORE CURRENTS WILL CREATE DANGEROUS SWIMMING 
CONDITIONS...ESPECIALLY FOR INEXPERIENCED SWIMMERS. 

.LOX WATCHES/WARNINGS/ADVISORIES...
HIGH RIP CURRENT RISK (SEE LAXSRFLOX).
BEACH HAZARDS STATEMENT (SEE LAXCFWLOX).

&&
$$

PUBLIC...RAT/KJ
AVIATION...CAK
MARINE...SWEET
BEACH HAZARDS...CAK
SYNOPSIS...RAT/KJ/WF

WWW.WEATHER.GOV/LOSANGELES




Return to Home page


Western Regional Climate Center, wrcc@dri.edu