Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 190002 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
500 PM PDT THU SEP 18 2014

...UPDATED AVIATION DISCUSSION...

.SYNOPSIS...
A LOW PRESSURE SYSTEM TO THE NORTH AND ONSHORE FLOW WILL BRING
DRASTICALLY COOLER CONDITIONS THROUGH SATURDAY...WITH INCREASED LOW
CLOUDS...FOG AND POSSIBLE DRIZZLE. TEMPERATURES WILL WARM TO ABOVE
NORMAL EARLY NEXT WEEK AS A HIGH MOVES IN. ANOTHER LOW MAY APPROACH
BY MIDWEEK TO DEEPEN THE MARINE LAYER AND START A COOLING TREND.

&&

.SHORT TERM (TODAY-SUN)...
AN UPPER LEVEL TROUGH OFF NORTHERN CALIFORNIA HAS PRODUCED A WEAK
BOUNDARY THAT IS CURRENTLY WORKING INTO SBA COUNTY. THIS HAS PUSH
THE RIDGE THAT BROUGHT THE HEAT FROM EARLIER THIS WEEK OFF TO THE
EAST...WHILE TURNING THE LIGHT OFFSHORE GRADIENTS TO MODERATELY
ONSHORE. THIS ALL ADDS UP TO TEMPERATURES DROPPING 10 TO 15 DEGREES
FROM YESTERDAY OVER NEARLY EVERY COUNTY. CURIOUSLY ENOUGH THE
CENTRAL COAST IS A FEW DEGREES WARMER...WITH THE ONLY EXPLANATION
BEING THE WIPING OF THE MARINE LAYER STRATUS THANKS TO THE BOUNDARY.
GUSTY SOUTHWEST WINDS WILL CONTINUE OVER THE INTERIOR SECTIONS...BUT
LOOKS TO STAY UNDER ADVISORY CRITERIA. ONE MORE WEAK SUNDOWNER LOOKS
LIKELY...BUT SHOULD STAY CONFINED TO THE WESTERN CANYONS AND WELL
BELOW ADVISORY.

THE TROUGH IS EXPECTED TO CUT OFF INTO A WEAK LOW THAT WILL WOBBLE
AROUND CALIFORNIA THROUGH SUNDAY. THIS SHOULD CONTINUE THE COOLING
TREND INTO FRIDAY. THE BIG QUESTION MARK IS HOW THE CLOUDS WILL
RESPOND. ALL COMPUTER PROJECTIONS ARE SHOWING AN EXTENSIVE LOW-LEVEL
MOIST LAYER FROM THE COAST PUSHING DEEP INTO THE VALLEYS BY FRIDAY
MORNING. THE MARINE INVERSION SHOULD WEAKEN OVER THE AREA
HOWEVER...MUCH LIKE IT DID OVER THE CENTRAL COAST TODAY. ADDING TO
THAT...THERE ISNT A WHOLE LOT OF CLOUDS TO BEGIN WITH OFF THE COAST
AND THE OCEAN WATERS ARE AS WARM AS THEY EVER GET. ALL OF THIS
LEAVES THIS FORECASTER STUMPED AS TO WHAT THE CLOUDS WILL LOOK LIKE
TOMORROW MORNING. MADE LITTLE IF ANY CHANGES TO THE PREVIOUS
FORECAST AS A RESULT. THE MOST LIKELY OUTCOME IS PLENTY OF
STRATOCUMULUS OVER THE AREA...BUT WITH LOTS OF RANDOM CLEAR GAPS AND
ANYTHING BUT SOLID. DRIZZLE IS A POSSIBILITY WITH THE LACK OF A
STRONG CAPPING INVERSION AND PLENTY OF TERRAIN EFFECTS TO PLAY WITH.
THEN AGAIN...IT COULD END UP STAYING CLEAR OVER MOST OF THE AREA.

ON SATURDAY...WITH THE LOW WOBBLING INTO EAST-CENTRAL
CALIFORNIA...ONSHORE GRADIENTS WEAKEN IN THE MORNING. WHATEVER CLOUD
COVER WE SEE ON FRIDAY...SHOULD BE DECREASED ON SATURDAY AS A
RESULT. TEMPERATURES LOOK TO RISE A LITTLE AS A RESULT. WITH THE
LOW MOVING INTO NEVADA AND ANOTHER TROUGH APPROACHING NORTHERN
CALIFORNIA ON SUNDAY...ONSHORE PRESSURE GRADIENTS SHOULD INCREASE
ONCE AGAIN. PREVIOUS FORECASTS CALLED FOR THE WARMING TREND TO
COMMENCE...SO WHILE CURRENT PROJECTIONS SUGGEST A SLIGHT COOLING
TREND ON SUNDAY...WENT WITH LITTLE CHANGE. IF COMPUTER MODELS KEEP
HINTING AT THIS...WE SHOULD SEE THAT DROP IN TEMPERATURES. GUSTY
ONSHORE WINDS LOOK TO RETURN AS WELL TO THE INTERIOR SECTIONS.

.LONG TERM (MON-THU)...
MODELS STILL HOLDING COURSE WITH THE WARMER SOLUTIONS...BUT NOT EVEN
HINTING AT THE SCORCHING HOT SOLUTIONS THAT PREVIOUS RUNS WERE
SUGGESTING. THE EDGE OF A LARGE TROUGH LOOKS TO CLIP NORTHERN
CALIFORNIA ON MONDAY...WHILE THE HIGH CURRENTLY OVER TEXAS SQUEEZES
INTO NORTHERN BAJA. WITH THE PROXIMITY OF THE HIGH...WE SHOULD SEE A
WARMING TREND MONDAY AND TUESDAY...ALONG WITH WEAKER ONSHORE
PRESSURE GRADIENTS AND LESS CLOUD COVER.

THE GFS AND ECMWF...BACKED BY A MAJORITY OF THE GFS
ENSEMBLES...SUGGEST A SECONDARY LOW DROPPING DOWN WITH THE
AFOREMENTIONED TROUGH. THIS WOULD CAUSE THE TROUGH...BLOCKED BY A
HUGE RIDGE (THAT WAS PREVIOUSLY MODELED TO BE OVER THE SOUTHWEST)
OVER THE EASTERN HALF OF THE COUNTRY...TO DIP INTO CENTRAL OR
SOUTHERN CALIFORNIA BY THURSDAY OR FRIDAY. A LOT COULD HAPPEN WITH
THIS TYPE OF PATTERN...INCLUDING PRECIPITATION...BUT FOR NOW WE WILL
START LOWERING TEMPERATURES SOME AND SEE WHAT THE NEXT MODELS SAY.

&&

.AVIATION...19/0000Z...MODERATE CONFIDENCE OVERALL IN THE 00Z TAFS
DUE TO UNCERTAINTIES WITH TIMING AND EXTENT OF LOW CLOUDS TONIGHT
AND FRI FOR ALL THE COAST AND ADJACENT VLY AIRFIELDS. HOWEVER...
THERE IS GENERALLY HI CONFIDENCE THAT LOW CLOUDS AND MOSTLY IFR/MVFR
CONDITIONS WILL AFFECT THESE AIRFIELDS DURING THE TAF PERIOD. THE
ONSET OF LOW CLOUDS WILL RANGE FROM TAF ISSUANCE TIME AT KLAX TO 09Z
AT KSBA. ALSO...THE TIMING OF THE ONSET OF THE LOW CLOUDS MAY BE OFF
PLUS/MINUS 1-2 HOURS EXCEPT FOR KLAX. THERE IS ALSO UNCERTAINTY TO
THE TIMING OF THE LOW CLOUDS SCATTERING OUT LATE FRI MORNING OR FRI
AFTERNOON AT KPRB...KSBP...KSMX...KLGB...KBUR AND KVNY WHICH MAY BE
OFF PLUS/MINUS AN HOUR OR TWO. FOR KSBA...KOXR...KLAX AND KLGB...THE
LOW CLOUDS ARE EXPECTED TO LINGER THRU FRI AFTERNOON. THERE IS ALSO
A 20-30 PERCENT CHANCE THAT THE LOW CLOUDS MAY BE INTERMITTENT AT
TIMES...ESPECIALLY S OF POINT CONCEPTION. FOR KPMD AND KWJF...HI
CONFIDENCE IN VFR CONDITIONS THRU FRI...WITH GUSTY SW WINDS EARLY
THIS EVENING.

KLAX...MODERATE TO HI CONFIDENCE OVERALL IN THE 00Z TAF. LOW CLOUDS
AND MVFR CONDITIONS AT THE AIRFIELD AT TAF ISSUANCE TIME MAY BE
INTERMITTENT FOR A WHILE THIS EVENING. THERE IS ALSO A 20 PERCENT
CHANCE THE LOW CLOUDS COULD SCATTER OUT MID TO LATE FRI AFTERNOON.
OTHERWISE...THE LOW CLOUDS SHOULD PERSIST FOR THE MOST PART THRU FRI
EVENING.

KBUR...MODERATE CONFIDENCE OVERALL IN THE 00Z TAF DUE TO
UNCERTAINTIES WITH TIMING OF LOW CLOUDS THIS EVENING AND FRI. THE
LOW CLOUDS WITH MVFR CIGS SHOULD DEVELOP AROUND 06Z THEN LINGER THRU
21Z. THE TIMING OF THE ONSET AND DISSIPATION OF THE LOW CLOUDS MAY
BE OFF PLUS/MINUS 1-2 HOURS. OTHERWISE...VFR CONDITIONS CAN BE
EXPECTED.

&&

.MARINE...18/200 PM.
SMALL CRAFT ADVISORY CONDITIONS IN THE VICINITY OF THE NORTHERN
CHANNEL ISLANDS AND EXTENDING SOUTHEAST TO SANTA CATALINA ISLAND
WILL LIKELY EXIST THIS AFTERNOON THROUGH LATER TONIGHT. THERE IS A
CHANCE SMALL CRAFT ADVISORY CONDITIONS WILL REDEVELOP EACH AFTERNOON
AND CONTINUE THROUGH THE LATE EVENING EACH DAY SUNDAY THROUGH
TUESDAY. THERE IS A CHANCE THE NORTHWEST WINDS WILL INCREASE TO
GALES THURSDAY AFTERNOON IN THE VICINITY OF THE NORTHERN ISLANDS TO
SAN NICOLAS ISLAND. SEAS FROM THE LOW PRESSURE SYSTEM WEST OF POINT
ARENA THIS MORNING WILL ARRIVE FROM THE WEST NORTHWEST DIRECTION
THROUGH SATURDAY NIGHT. THE SOUTH SWELL WILL CONTINUE TO SUBSIDE
WHILE LINGERING THROUGH SATURDAY. A 982MB LOW PRESSURE SYSTEM IS
EXPECTED TO DEVELOP NEXT WEEK TUESDAY OVER THE EASTERN PACIFIC AND
SWELLS GENERATED BY NEAR STORM FORCE WINDS ARE EXPECTED TO ARRIVE
FROM 295-310 DEGREES WEDNESDAY AFTERNOON AND PEAK WEDNESDAY NIGHT.

&&

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

&&

$$

PUBLIC...KITTELL
AVIATION...SIRARD
MARINE...30
SYNOPSIS...SETO

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