Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 040016 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
515 PM PDT SUN MAY 3 2015

UPDATED AVIATION SECTION

.SYNOPSIS...
NIGHT THROUGH MORNING LOW CLOUDS AND FOG WILL CONTINUE THROUGH
MIDWEEK WITH ONSHORE FLOW AND WEAK LOW PRESSURE. ANOTHER LOW WILL
MOVE IN THURSDAY WITH POSSIBLE RAIN SHOWERS INTO THE END OF THE
WEEK. THE TEMPERATURES SHOULD REMAIN BELOW NORMAL ALL WEEK LONG.

&&

.SHORT TERM (TODAY-WED)...
WEAK TROUGH OF LOW PRESSURE OFF THE COAST OF SOUTHERN CALIFORNIA
WILL CONTINUE TO SLOWLY TRACK EASTWARD...WITH THE LOW
BECOMING CENTERED JUST OFF OF POINT CONCEPTION BY THIS EVENING.
MEANWHILE...PRESSURE GRADIENTS ARE TRENDING ONSHORE WITH CURRENT
LAX-DAGGETT GRADIENT AT +7.2 MB. THE COMBINATION OF THE UPPER LOW
AND STRENGTHENING ONSHORE FLOW BROUGHT A DEEPER MARINE
LAYER THIS MORNING...WITH ACARS SOUNDING SHOWING A DEPTH
AROUND 2500 FEET OVER THE LA BASIN. AS A RESULT...LOW CLOUDS
WERE EXTENSIVE ACROSS COASTAL AND VALLEY AREAS THIS MORNING ALONG
WITH COOLER DAYTIME TEMPERATURES ACROSS MUCH OF THE DISTRICT.
ONSHORE FLOW WILL CONTINUE TO INCREASE THIS AFTERNOON...RESULTING IN
GUSTY ONSHORE WINDS ACROSS THE MOUNTAINS AND ANTELOPE VALLEY...WHERE
GUSTS BETWEEN 30 AND 40 MPH CAN GENERALLY BE EXPECTED. ISOLATED WIND
GUSTS AS HIGH AS 50 MPH CAN BE EXPECTED NEAR LAKE PALMDALE. WITH SOME
INCREASING INSTABILITY...SHOULD SEE SOME CUMULUS BUILDUPS OVER THE
LOCAL MOUNTAINS THIS AFTERNOON AND AGAIN MONDAY AFTERNOON. HOWEVER
NO SHOWERS OR THUNDERSTORMS ARE EXPECTED ACROSS OUR FORECAST AREA
DUE TO THE VERY LIMITED AVAILABLE MOISTURE.

AS THE WEAK UPPER LEVEL LOW PRESSURE SYSTEM MOVES OVER SOUTHERN
CALIFORNIA OVERNIGHT...THERE WILL LIKELY BE ADDITIONAL DEEPENING
OF THE MARINE LAYER TO AROUND 3000 FEET...WITH LITTLE CHANGE INTO
TUESDAY. AS A RESULT...LOW CLOUDS AND FOG WILL LIKELY SPREAD
INTO THE LOWER COASTAL SLOPES ALONG WITH SOME PATCHY DRIZZLE THE
NEXT COUPLE OF DAYS. THE COOLING TREND WILL CONTINUE...ALONG WITH
THE GUSTY ONSHORE WINDS IN THE MOUNTAINS AND ANTELOPE VALLEY. ONCE
AGAIN...WINDS COULD LOCALLY GUST AS HIGH AS 50 MPH NEAR LAKE PALMDALE
THE NEXT COUPLE OF DAYS.

A SECONDARY LOW PRESSURE SYSTEM WILL BEGIN TO DEVELOP ACROSS THE
WEST COAST ON WEDNESDAY...WITH CYCLONIC FLOW AND STRONG ONSHORE FLOW
CONTINUING TO BRING COOL AND CLOUDY CONDITIONS TO THE REGION. BY
WEDNESDAY...WINDS COULD APPROACH WIND ADVISORY LEVEL THRESHOLDS
FOR THE ANTELOPE VALLEY.

.LONG TERM (THU-SUN)...
GFS AND ECMWF MODELS CONTINUE TO DROP COLD UPPER LEVEL LOW PRESSURE
SOUTHWARD INTO CALIFORNIA SOMETIME IN THE THURSDAY INTO FRIDAY TIME
FRAME BUT STILL SOME TIMING AND LOCATION DIFFERENCES IN RESPECT
TO THE CENTER OF THE LOW. IT IS FAIRLY CERTAIN THAT THIS SYSTEM
WILL BRING COOLER AND CLOUDY WEATHER TO THE DISTRICT ALONG WITH WINDY
CONDITIONS IN THE MOUNTAINS AND DESERTS. LONG RANGE MODELS CONTINUE
TO TREND FURTHER WEST WITH THE LOW PRESSURE SYSTEM WITH A 90 KNOT JET
ON BACK SIDE OF LOW. WHILE THIS SYSTEM DOES NOT HAVE A WHOLE LOT OF
MOISTURE...IT DOES HAVE SOME DYNAMICS AND ASSOCIATED HEIGHT FALLS
ALONG WITH UNUSUALLY COLD AIR ALOFT (-25 DEGREES CELSIUS AT 500 MB
BY FRIDAY MORNING) FOR A MAY STORM. WITH THIS IN MIND...THERE IS A
THREAT OF SHOWERS SOMETIME IN THE THURSDAY INTO FRIDAY TIME
FRAME...BUT STILL UNCERTAIN ON EXACT TIMING AND EXTENT OF SHOWER
ACTIVITY. FOR NOW WILL KEEP WITH 20-30 PERCENT POPS...WITH HIGHEST
POPS FOCUSED OVER LA COUNTY WHERE THERE WILL BE BETTER CYCLONIC FLOW
ALOFT. AND DEPENDING ON EXACT TRACK OF THIS SYSTEM...CANNOT TOTALLY
RULE OUT THE POSSIBILITY OF ISOLATED THUNDERSTORM ACTIVITY BUT THOSE
DETAILS WILL BECOME MORE APPARENT IN THE NEXT COUPLE OF DAYS.

WEAK UPPER LEVEL RIDGE BUILDS IN FOR THE WEEKEND BRINGING A WARMING
AND DRYING TREND.

&&

.AVIATION...04/0015Z.

AT 1640Z...THE MARINE INVERSION AT KLAX WAS BASED AT 1600 FEET. THE
TOP OF THE INVERSION WAS 4100 FEET WITH A TEMPERATURE OF 16 DEGREES
CELSIUS.

LOW CONFIDENCE IN TIME OF ARRIVAL OF IFR TO MVFR CONDITIONS. IFR TO
MVFR CONDITIONS COULD ARRIVE AS EARLY AS 03Z AT COASTAL
TERMINALS...BUT MORE LIKELY BETWEEN 06Z AND 10Z...THEN SPREAD
QUICKLY INTO VALLEY TERMINALS. THERE IS A 40 PERCENT CHANCE OF MVFR
CONDITIONS OR CEILINGS AT OR BELOW 5000 FEET LINGERING INTO MONDAY
AFTERNOON AT ALL COASTAL AND VALLEY TERMINALS.

KLAX...MVFR CONDITIONS COULD ARRIVE AS EARLY AS 03Z...BUT MORE
LIKELY BETWEEN 08Z AND 10Z. THERE IS A 40 PERCENT CHANCE OF MVFR
CONDITIONS OR CEILINGS AT OR BELOW 5000 FEET LINGERING THROUGHOUT
MONDAY AFTERNOON.

KBUR...MVFR CONDITIONS COULD ARRIVE AS EARLY AS 07Z...BUT MORE
LIKELY BETWEEN 10Z AND 13Z. THERE IS A 40 PERCENT CHANCE OF MVFR
CONDITIONS OR CEILINGS AT OR BELOW 5000 FEET LINGERING THROUGHOUT
MONDAY AFTERNOON.

&&

.MARINE...03/200 PM...

FOR THE OUTER WATERS...HIGH CONFIDENCE IN NORTHWEST WINDS REMAINING
BELOW SMALL CRAFT ADVISORY LEVELS THROUGH MONDAY. BY TUESDAY...THE
NORTHWEST WINDS WILL INCREASE...WITH MODERATE CONFIDENCE IN SMALL
CRAFT ADVISORY CONDITIONS DEVELOPING FROM SAN NICOLAS ISLAND
NORTHWARD...WITH THE ADVISORY LEVEL WINDS CONTINUING THROUGH
THURSDAY.

FOR THE INNER WATERS...HIGH CONFIDENCE IN WEST TO NORTHWEST WINDS
REMAINING BELOW SMALL CRAFT ADVISORY LEVELS THROUGH THURSDAY. HOWEVER
THERE WILL BE A SLIGHT CHANCE OF SMALL CRAFT ADVISORY LEVEL GUSTS
ACROSS THE WESTERN HALF OF THE SANTA BARBARA CHANNEL TUESDAY THROUGH
THURSDAY.

A LONG PERIOD (20-24 SECOND) SOUTHERLY SWELL WILL MOVE INTO THE
COASTAL WATERS TODAY...AND REMAIN THROUGH EARLY THIS WEEK.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY (SEE LAXCFWLOX).
MARINE WEATHER STATEMENT (SEE LAXMWSLOX).

&&

$$

PUBLIC...GOMBERG
AVIATION...HALL
MARINE...RAT
SYNOPSIS...SWEET

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