Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 190601
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1000 PM PST THU DEC 18 2014

...UPDATED AVIATION SECTION...

.SYNOPSIS...

WEAK HIGH PRESSURE ALOFT WILL BREAK DOWN FRIDAY AS A WEAK STORM
SYSTEM WILL BRING ANOTHER CHANCE OF LIGHT RAIN FROM FRIDAY
THROUGH FRIDAY NIGHT. HIGH PRESSURE WILL BUILD OVER THE AREA THIS
WEEKEND...BRINGING DRY WEATHER AND A WARMING TREND THROUGH THE
MIDDLE OF NEXT WEEK.

&&

.UPDATE...

A DIRTY RIDGE OF HIGH PRESSURE IS MOVING OVER THE REGION THIS
EVENING FROM THE WEST. AN UPSTREAM COLD FRONT ABOUT 500 MILES
WEST OF POINT CONCEPTION WILL MOVE INTO THE REGION ON FRIDAY. THE
STORM SYSTEM IS RATHER WEAK...BUT RAIN OR SHOWERS CANNOT BE RULED
OUT. THE CURRENT PACKAGE HAD MENTIONS OF RAIN OR SHOWERS...WHICH
SEEMS AGREEABLE BASED UPON 00Z NAM-WRF 850 MB MIXING RATIOS IN
EXCESS OF 6 G/KG WITH THE STORM SYSTEM. THE BEST CHANCE OF
RAINFALL WILL BE FOR AREAS NORTH OF POINT CONCEPTION...WITH THE
HIGHEST RAINFALL AMOUNTS EXPECTED IN NORTHWEST SAN LUIS OBISPO
COUNTY. A FEW TWEAKS WERE MADE TO THE TIMING OF THE FRONTAL
BOUNDARY. SLIGHT CHANCE POPS WERE ALSO ADDED FOR THE ANTELOPE
VALLEY AS A FEW SHOWERS CANNOT BE RULED OUT IN THE MOJAVE DESERT.

&&

.PREV DISCUSSION...

SHORT TERM...A FEW LIGHT SHOWERS WERE OCCURRING OVER THE EASTERN
SAN GABRIEL MOUNTAIN RANGE THIS AFTERNOON...OTHERWISE SKIES
REMAINED PARTLY TO MOSTLY CLOUDY. HIGH TEMPS WILL BE FAIRLY
SIMILAR TO YESTERDAY IN MOST AREAS. THE MAIN TROUGH AXIS HAS MOVED
EAST INTO ARIZ. A BRIEF SHORTWAVE RIDGE WILL BUILD IN AS ANOTHER
WEAK UPPER TROUGH APPROACHES THE FORECAST AREA WITHIN BROAD NW
FLOW ALOFT. A WEAK COLD FRONT ASSOCIATED WITH THIS TROUGH THAT
WILL BRING LIGHT SHOWERS TO AREAS N OF POINT CONCEPTION...MOSTLY
LESS THAN A TENTH OF AN INCH...EXCEPT FOR THE NW PORTION OF SLO
COUNTY WHERE LOCALLY HIGHER AMOUNTS CAN OCCUR. THE COLD FRONT
WEAKENS FURTHER AS IT MOVES INTO VENTURA AND LOS ANGELES COUNTIES
FRIDAY EVENING/OVERNIGHT HOURS. WITH 850 MB WINDS (5,000 FT)
EXPECTED TO BE OUT OF THE NW...THIS WILL NOT BE CONDUCIVE FOR ANY
SHOWERS TO HOLD TOGETHER AS IT APPROACHES THE VENTURA AND LOS
ANGELS COUNTY COAST AND VALLEYS. HOWEVER...WITH ALL THE LOW LEVEL
MOISTURE ALREADY IN PLACE...HAVE PUT IN SLIGHT CHANCE POPS FOR
LA/VTU COUNTIES FRIDAY EVENING THROUGH THE OVERNIGHT HOURS. AS THE
FRONT PUSHES EAST...CLOUDS WILL BEGIN TO BANK UP AGAINST THE
NORTHERN SLOPES OF THE SBA/VTU AND NW PORTION OF LA COUNTY
MOUNTAINS FRIDAY NIGHT INTO SATURDAY MORNING. A FEW LIGHT SHOWERS
WILL BE POSSIBLE OR A FEW SNOW FLURRIES ABOVE 6,000 FT. THERE MAY
BE AN INCH OF TOTAL SNOW ACCUMULATION ABOVE 6,500 FT.

FOR SATURDAY...THERE WILL CONTINUE TO BE SOME LINGERING LOW LEVEL
MOISTURE IN THE MORNING...ESPECIALLY AROUND THE FOOTHILLS...SO WILL
GO WITH PARTLY CLOUDY SKIES...EXCEPT MOSTLY CLOUDY FOR THE
MOUNTAINS. HIGH TEMPS WILL BE A FEW DEGREES WARMER WITH MOST AREAS
IN THE MID TO UPPER 60S WEST OF THE MOUNTAINS.

AS THE TROUGH MOVES TO THE EAST...A NORTHERLY SURFACE PRESSURE
GRADIENT WILL DEVELOP SATURDAY AFTERNOON BRINGING GUSTY NORTHWEST TO
NORTH WINDS TO THE SANTA BARBARA COUNTY MOUNTAINS AND ADJACENT SBA
SOUTH COAST AS WELL AS THE I-5 CORRIDOR. A LOW END WIND ADVISORY
MIGHT BE NEEDED FOR THIS AREA. NORTHERLY WINDS WILL ALSO STRENGTHEN
THROUGH SANTA CLARITA...SAN FERNANDO VALLEY AND POSSIBLY INTO WEST
LA SATURDAY NIGHT BUT REMAIN BELOW ADVISORY THRESHOLDS. WITH BETTER
CLEARING EXPECTED ON SATURDAY NIGHT...THERE WILL BE A BETTER CHANCE
FOR SOME PATCHY DENSE FOG TO DEVELOP ACROSS THE SALINAS
VALLEY...WIND PROTECTED AREAS ACROSS THE CENTRAL COAST AND A FEW LOW
LYING LA/VTU/SBA VALLEY LOCATIONS.

SYNOPTICALLY...A RELATIVELY STRONG UPPER HIGH WILL BUILD IN OVER THE
EASTERN PACIFIC ON SUNDAY NUDGING HEIGHTS AND THICKNESS LVLS HIGHER
OVER THE FORECAST AREA. EXPECT MOSTLY SUNNY SKIES WITH HIGH TEMPS
EXPECTED TO REACH THE LOWER TO MID 70S FOR THE LA/VTU/SBA COUNTY
VALLEYS AND INLAND COASTAL AREAS. HI TEMPS ACROSS THE CENTRAL COAST
COULD BE A FEW DEGREES WARMER DUE TO SOME OFFSHORE FLOW
COMING OFF THE SAN LUCIA MTNS.

LONG TERM...BOTH THE GFS AND ECMWF ARE IN PRETTY GOOD AGREEMENT
KEEPING THE UPPER HIGH SITTING OVER THE EASTERN PACIFIC WITH
HEIGHTS PEAKING AT 588DM OVER OUR FORECAST AREA. SKIES WILL REMAIN
MOSTLY CLEAR THROUGH THE PERIOD WITH CONTINUED GUSTY NORTHERLY
WINDS ON MONDAY. A 1030 MB SURFACE HIGH IS PROGGED TO SET UP BY
MONDAY NIGHT INTO TUESDAY. THIS WILL CAUSE OFFSHORE WINDS TO
DEVELOP. THERE WILL BE SOME MARGINAL UPPER LEVEL SUPPORT ALLOWING
FOR A MODERATE SANTA ANA WIND EVENT. HIGH TEMPS WILL PEAK ON TUE
WITH SOME COAST AND COASTAL VALLEYS LOCATIONS REACHING THE LOWER
80S...INCLUDING THE CENTRAL COAST. BY WEDNESDAY/THURSDAY...ANOTHER
UPPER TROUGH WILL BE DIGGING DOWN ACROSS OREGON/NRN NEVADA CAUSING
HEIGHTS AND THICKNESS LEVELS TO DROP RAPIDLY. HIGH TEMPS ARE
EXPECTED TO LOWER 4 TO 6 DEGREES FOR COAST AND VALLEYS...WITH MORE
SIGNIFICANT COOLING EXPECTED ON THURSDAY. MODELS COOL THINGS OFF
AN ADDITIONAL 5 TO 8 DEGREES TO THE MID 60S IN MOST AREAS. I AM
NOT THAT CONFIDENT THAT WE WILL SEE HIGH TEMPS ONLY IN THE MID 60S
AS THERE WILL CONTINUE TO BE AN OFFSHORE COMPONENT FOR THE AREA.
HOWEVER...IF COLDER AIR DOES FILTER INTO THE INTERIOR REGION AS
THE GFS SUGGESTS...WE COULD SEE ANOTHER BURST OF GUSTY SANTA ANA
WINDS ON THURSDAY...BUT TEMPS WILL BE MUCH COOLER THAN THE PRIOR
TUESDAY.

&&

.AVIATION...19/0600Z.

MARINE LAYER AT LAX AT 06Z IS NONE.

WITH NO MARINE LAYER INVERSION AND MID-HIGH CLOUDS MOVING THROUGH
THE AREA TONIGHT...CONFIDENCE IS LOW TO MODERATE FOR MUCH OF THE
AREA. LOW CONFIDENCE FOR TAF SITES IN SLO AND SBA COUNTY. MODERATE
CONFIDENCE ELSEWHERE. THERE IS A 40 PERCENT CHANCE THAT LIFR
CONDITIONS WILL NOT DEVELOP AT KPRB TONIGHT. ALSO A 40 PERCENT
CHANCE THAT KSBP AND KSMX WILL NOT FALL INTO THE LIFR CATEGORY.
THERE IS A 20-40 PERCENT CHANCE THAT COASTAL SITES SOUTH OF POINT
CONCEPTION WILL HAVE MVFR CONDITIONS FROM 08-18Z...WITH KSBA AND
KOXR HAVING THE BEST CHANCES. A WEAK DISTURBANCE WITH ISOLATED
SHOWERS WILL MOVE ACROSS THE AREA FRIDAY AFTERNOON. BEST CHANCE FOR
SHOWERS WILL BE IN SLO AND SBA COUNTY. THERE IS 20-30 PERCENT CHANCE
OF MVFR CONDITIONS AT MOST SITES TOMORROW AFTERNOON.

KLAX...MODERATE CONFIDENCE IN THE 06Z TAF. THERE IS A 20 PERCENT
CHANCE OF MVFR CONDITIONS AFTER 12Z.

KBUR...MODERATE CONFIDENCE IN 06Z TAF. THERE IS A 20 PERCENT CHANCE
OF MVFR CONDITIONS AFTER 18Z.

&&

MARINE...18/900 PM.

A SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS HAS BEEN ADDED. THERE IS
A CHANCE THAT THE TIME OF ARRIVAL OF HAZARDOUS SEAS COULD PLUS OR
MINUS 3 HOURS. THE TIME OF ARRIVAL SHOULD BECOME A LITTLE MORE
CERTAIN OVER THE NEXT 12 HOURS OR SO. A SMALL CRAFT ADVISORY FOR
HAZARDOUS SEAS WILL LIKELY BE ADDED FOR THE SOUTHERN PORTION OF
THE OUTER WATERS OVER THE NEXT 12 HOURS.

THE WEST TO NORTHWEST SWELL WILL LIKELY CREATE BREAKING WAVES AT
THE HARBOR ENTRANCES SUCH AS MORRO BAY AND VENTURA HARBOR. MORRO
BAY IMPACTS COULD BEGIN AS SOON AS FRIDAY EVENING...OR AS LATE AS
EARLY SATURDAY MORNING. VENTURA HARBOR COULD BE IMPACTED AS SOON
AS SATURDAY OR AS LATE AS SATURDAY EVENING. BOTH HARBORS SHOULD
SEE IMPACTS THROUGH SUNDAY MORNING.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY (SEE LAXCFWLOX).
COASTAL FLOOD ADVISORY (SEE LAXCFWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
MARINE WEATHER STATEMENT (SEE LAXMWSLOX).

&&

$$

PUBLIC...HALL
AVIATION...SUKUP
MARINE...HALL
SYNOPSIS...HALL

WWW.WEATHER.GOV/LOSANGELES




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