Area Forecast Discussion
Issued by NWS Los Angeles, CA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KLOX 060615 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1115 PM PDT TUE MAY 5 2015

UPDATED AVIATION SECTION

.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...06/0615Z.

AT 0555Z...THE MARINE INVERSION AT KLAX WAS BASED AROUND 4400 FEET.
THE TOP OF THE INVERSION WAS AROUND 6500 FEET WITH A TEMPERATURE OF
10 DEGREES CELSIUS.

PREDOMINANT MVFR CONDITIONS WILL CONTINUE TO SPREAD INTO COASTAL AND
VALLEY TERMINALS THROUGH 14Z. THERE IS A CHANCE THAT COASTAL
TERMINALS COULD STRUGGLE TO CLEAR ON WEDNESDAY WITH SCATTERED TO
BROKEN CEILINGS ABOVE 3000 FEET LINGERING INTO THE AFTERNOON HOURS.
GUSTY ONSHORE WINDS WILL DEVELOP THE ANTELOPE VALLEY TERMINALS
BETWEEN WEDNESDAY AFTERNOON AND WEDNESDAY EVENING. THERE IS A CHANCE
OF LOWERING VISIBILITIES IN BLOWING DUST FOR THE ANTELOPE VALLEY
TERMINALS.

KLAX AND KBUR...PREDOMINANT MVFR CONDITIONS WILL SPREAD IN BETWEEN
06Z AND 10Z. THERE IS A 50 PERCENT CHANCE THAT MVFR TO VFR
CONDITIONS WITH CEILINGS BELOW 5000 FEET COULD LINGER UNTIL AS LATE
AS 23Z WEDNESDAY.

&&

.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).

&&
$$

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

WWW.WEATHER.GOV/LOSANGELES





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.