Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 060334
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
830 PM PDT TUE MAY 5 2015

.SYNOPSIS...

STRONG ONSHORE FLOW WILL BRING EXTENSIVE LOW CLOUDS INTO THE LOWER
COASTAL SLOPES ALONG WITH PATCHY DRIZZLE THROUGH WEDNESDAY. A LOW
PRESSURE SYSTEM WILL ARRIVE WEDNESDAY NIGHT BRINGING A CHANCE OF
SHOWERS AND THUNDERSTORMS THROUGH FRIDAY. GUSTY ONSHORE WINDS WILL
CONTINUE IN THE MOUNTAINS AND DESERTS THE NEXT FEW DAYS.
TEMPERATURES WILL REMAIN BELOW NORMAL THIS WEEK THEN WARM TO ABOVE
NORMAL BY NEXT WEEK AS HIGH PRESSURE BUILDS IN.

&&

.SHORT TERM (TONIGHT-SAT)...
WEAK UPPER LEVEL TROUGH COMBINED WITH STRONG ONSHORE FLOW BROUGHT
A 4500 FOOT MARINE LAYER DEPTH TO THE REGION TODAY. AS A RESULT...CLOUDS
PERSISTED THROUGH THE AFTERNOON HOURS ACROSS MUCH OF LOS ANGELES
AND VENTURA COUNTIES...KEEPING TEMPERATURES ON THE COOLER SIDE TODAY.
THE STRONG ONSHORE GRADIENTS (WITH LAX-DAGGETT PEAKING AT +10.2 MB THIS
AFTERNOON) BROUGHT ANOTHER ROUND OF GUSTY ONSHORE WINDS IN THE MOUNTAINS
AND ANTELOPE VALLEY. A WIND ADVISORY REMAINS IN EFFECT THROUGH TOMORROW
FOR THE ANTELOPE VALLEY...WHERE ISOLATED GUSTS AS HIGH AS 55 MPH WILL
CONTINUE IN THE FOOTHILLS. ANOTHER CLOUDY COOL DAY ON TAP FOR
SOUTHWEST CALIFORNIA ON WEDNESDAY...WITH CLOUDS LIKELY STRUGGLING TO
CLEAR ONCE AGAIN IN THE AFTERNOON HOURS.

THE BIG WEATHER STORY WILL BE THE COLD LOW PRESSURE SYSTEM ORIGINATING
IN THE GULF OF ALASKA DIGGING SOUTHWARD INTO CALIFORNIA LATE WEDNESDAY
NIGHT INTO FRIDAY. THIS SYSTEM IS UNSEASONABLY COLD WITH 500 MB TEMPERATURES
FALLING AS LOW AS -28 DEGREES CELSIUS AND THICKNESSES BOTTOMING OUT
AROUND 540 DM. MODELS CONTINUE TO TREND THE COLDER AIR AND BETTER DYNAMICS
FURTHER WEST...ESPECIALLY THE NAM MODEL. WITH THIS IN MIND...THERE IS
INCREASING CONFIDENCE THAT SOUTHWEST CALIFORNIA WILL FEEL SOME IMPACTS
FROM THIS SYSTEM. MOISTURE IS SOMEWHAT LIMITED WITH THIS SYSTEM...WITH
PRECIPITABLE WATER VALUES GENERALLY RANGING BETWEEN .50 AND .75
INCHES. HOWEVER...THIS SYSTEM DOES POSSESS GOOD DYNAMICS AND COLD AIR
ALOFT...RESULTING IN A VERY UNSTABLE AIR MASS. THE FOCUS OF BEST DYNAMICS
AND INSTABILITY APPEARS TO BE SOMETIME BETWEEN THURSDAY AFTERNOON
AND THURSDAY NIGHT...ALTHOUGH MODELS HAVE BEEN WAVERING A BIT ON
TIMING OF BEST INSTABILITY FOR VENTURA AND LOS ANGELES COUNTIES. AS
THE COLD CORE SWINGS THROUGH THE AREA...00Z NAM CONTINUES TO SHOW A
WELL DEFINED POCKET OF INSTABILITY WITH LIFTED INDEX VALUES IN THE
-3 TO -6 RANGE AND CAPE VALUES APPROACHING 1000 J/KG. THESE ARE
RATHER IMPRESSIVE CONVECTIVE PARAMETERS FOR SOUTHERN CALIFORNIA. IN
EVENING UPDATE...HAVE EXPANDED THE THREAT OF THUNDERSTORMS
TO INCLUDE COASTAL AND VALLEY AREAS OF LOS ANGELES AND VENTURA COUNTIES
FOR THURSDAY NIGHT. WITH SUCH COLD AIR ALOFT AND INSTABILITY WITH
THIS SYSTEM...THE MAIN THREATS WITH ANY STORMS WILL BE HAIL AND
BRIEF HEAVY DOWNPOURS.

WITH THE TRAJECTORY OF THIS SYSTEM...IT WOULD APPEAR THAT LOS ANGELES
COUNTY AND POINTS SOUTH AND EAST WILL HAVE THE BEST MOIST CYCLONIC
FLOW PATTERN. IN COORDINATION WITH SAN DIEGO OFFICE...HAVE TRENDED POPS
HIGHER FOR LOS ANGELES COUNTY FOR THURSDAY NIGHT INTO FRIDAY MORNING.
ANOTHER POTENTIAL IMPACT WITH THIS STORM WILL BE UNUSUALLY LOW SNOW
LEVELS...MORE LIKE A TYPICAL WINTER SYSTEM. IN EVENING UPDATE...HAVE
LOWERED SNOW LEVELS TO AROUND 5000 FEET AS MODELS CONTINUE TO TREND
THE SYSTEM COLDER AND FURTHER WEST OVER OUR REGION. SNOW LEVELS
COULD FALL LOCALLY BELOW 5000 FEET IN HEAVIER CONVECTIVE SHOWERS. A
WINTER WEATHER ADVISORY WILL NEED TO BE CONSIDERED FOR THIS
STORM AS WE DRAW CLOSER TO THE EVENT DUE TO THE UNSEASONABLY LOW
SNOW LEVELS EXPECTED.


*** FROM PREVIOUS DISCUSSION ***

SATURDAY WILL BRING CLEARING SKIES BUT THERE IS A POSSIBILITY OF
LINGERING SHOWERS IN THE LOS ANGELES MOUNTAINS ESPECIALLY IN THE SAN
GABRIEL MOUNTAINS.

.LONG TERM (SUN-TUE)...
WARMING TEMPERATURES ON SUNDAY AND MONDAY THEN NEAR SEASONAL
TEMPERATURES ON TUESDAY BUT PARTLY CLOUDY AS A WEAK BOUNDARY MOVES
THROUGH THE REGION.

&&

.AVIATION...05/2345Z.

AT 2340Z...THE MARINE INVERSION AT KLAX WAS BASED AROUND 4500 FEET.
THE TOP OF THE INVERSION WAS AROUND 5700 FEET WITH A TEMPERATURE OF
9 DEGREES CELSIUS.

WEAK UPPER LEVEL TROUGH COMBINED WITH STRONG ONSHORE FLOW RESULTING
IN LOW CLOUDS LINGERING ACROSS MUCH OF VENTURA AND LOS ANGELES COUNTIES
THIS AFTERNOON...WITH PATCHIER COVERAGE FOR AREAS NORTH OF POINT
CONCEPTION. CONTINUED DEEP MARINE LAYER MOST LIKELY LINGERING IN THE
4000 TO 5000 FOOT RANGE THROUGH WEDNESDAY...WITH PATCHY DRIZZLE
POSSIBLE FOR AREAS SOUTH OF POINT CONCEPTION. MVFR TO VFR CIGS LIKELY
TO CONTINUE FOR MOST COASTAL/VALLEY TAF SITES THROUGH WEDNESDAY.
GUSTY ONSHORE WINDS EXPECTED FOR KPMD AND KWJF THROUGH THE
PERIOD...STRONGEST IN THE AFTERNOON HOURS...WHEN THERE WILL BE A CHANCE
OF LOWERING VSBYS DUE TO BLOWING DUST AND SAND.

KLAX AND KBUR...MVFR TO VFR CIGS WILL LIKELY CONTINUE THROUGH THE
PERIOD...WITH ONLY A 20 PERCENT CHANCE OF CLEARING ON WEDNESDAY
AFTERNOON.

&&

.MARINE...05/800 PM.

HIGH CONFIDENCE THAT SMALL CRAFT ADVISORIES WILL CONTINUE FOR THE
OUTER COASTAL WATERS THROUGH THURSDAY. SOUTH SWELL WILL GRADUALLY
SUBSIDE OVERNIGHT INTO WEDNESDAY. SLIGHT CHANCE OF THUNDERSTORMS
FOR THURSDAY INTO THURSDAY NIGHT ACROSS THE COASTAL WATERS AS
COLD LOW PRESSURE SYSTEM SWINGS SOUTHWARD ACROSS THE REGION.


&&

.LOX WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY (SEE LAXNPWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
HIGH SURF ADVISORY (SEE LAXCFWLOX).
BEACH HAZARD STATEMENT (SEE LAXCFWLOX).

&&
$$

PUBLIC...GOMBERG/KJ
AVIATION...GOMBERG
MARINE...GOMBERG
SYNOPSIS...GOMBERG

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