Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 190416
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
915 PDT THU SEP 18 2014

.SYNOPSIS...
WEAK UPPER LEVEL LOW PRESSURE WILL BRING BELOW NORMAL TEMPERATURES
TO MUCH OF THE REGION THROUGH THE WEEKEND. TEMPERATURES WILL LIKELY
WARM TO NEAR NORMAL EARLY NEXT WEEK AS THE UPPER LOW MOVES EAST AND
HIGH PRESSURE BRIEFLY RETURNS. ANOTHER TROUGH OF LOW PRESSURE MAY
BRING A COOLING TREND FOR THE SECOND HALF OF NEXT WEEK.

&&

.SHORT TERM (TONIGHT-SUN)...MUCH COOLER ACROSS THE FORECAST AREA
TODAY AS A COOLER AIRMASS MOVED INTO THE REGION WITH A DISSIPATING
COLD FRONT. THE FRONT LEFT BEHIND A MOIST AIRMASS AT LOW LEVELS WITH
STRATUS DEVELOPING THIS EVENING ALONG PORTIONS OF THE CENTRAL COAST
AND THE VTU/L.A. COUNTY COAST AND VTU COUNTY VLYS. THE LOW CLOUDS
ARE EXPECTED TO EXPAND QUICKLY OVERNIGHT AND COVER THE COAST AND
VLYS AFTER MIDNIGHT...INCLUDING THE SALINAS RIVER VLY. GUSTY WINDS
WILL CONTINUE IN THE ANTELOPE VLY OVERNIGHT BEFORE DIMINISHING
LATE.

AN UPPER LEVEL LOW ALONG THE CENTRAL CA COAST THIS EVENING WILL
DRIFT TO A POSITION NEAR OR JUST SW OF POINT CONCEPTION ON FRI. THE
UPPER LOW SHOULD DRIFT NE TO AROUND POINT CONCEPTION ON SAT...THEN
INLAND ACROSS CENTRAL CA INTO NEVADA SAT NIGHT AND SUN. THE MAIN
AFFECT OF THE UPPER LOW WILL BE TO DEEPEN THE MARINE LAYER WITH
PLENTY OF LOW CLOUDS FOR THE COAST AND VLYS NIGHT AND MORNING
HOURS...AND POSSIBLY EVEN INTO THE AFTERNOON. PATCHY DRIZZLE CAN
ALSO BE EXPECTED OVER THE COAST...VLYS AND COASTAL SLOPES LATER
TONIGHT INTO FRI MORNING...ALTHO THERE MAY ALSO BE PATCHY DRIZZLE IN
SOME AREAS FRI NIGHT INTO SAT MORNING. A FEW AFTERNOON CU BUILDUPS
CAN BE EXPECTED OVER THE MTNS FRI AND SAT...AND AN ISOLATED SHOWER
OR THUNDERSTORM CANNOT BE RULED OUT ESPECIALLY ON FRI...BUT AT THIS
TIME IT APPEARS THE CHANCES OF ANY THUNDERSTORMS ARE AROUND 10
PERCENT OR SO. THE UPPER LOW WILL CONTINUE TO BRING COOLER
TEMPERATURES TO ALL AREAS...WITH HIGHS NEAR NORMAL TO SLIGHTLY BELOW
NORMAL FRI AND SAT. TEMPS WILL WARM SLIGHTLY ON SUN BUT REMAIN NEAR
NORMAL TO SLIGHTLY BELOW NORMAL.

***FROM PREVIOUS DISCUSSION***

.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...18/800 PM
SMALL CRAFT ADVISORY CONDITIONS IN THE VICINITY OF THE NORTHERN
CHANNEL ISLANDS EXTENDING INTO THE WESTERN SANTA BARBARA CHANNEL AND
SOUTHWARD TO SAN NICOLAS ISLAND WILL CONTINUE THROUGH LATE TONIGHT.
WINDS ARE BEGINNING TO SUBSIDE OVER PZZ655 AND MAINLY LIGHT WINDS
EXIST ELSEWHERE. LARGER SHORT PERIOD SEAS WILL BEGIN TO SUBSIDE LATE
TONIGHT AS WINDS BEGIN TO EASE.

SEAS FROM LOW PRESSURE SYSTEM OVER THE NORTHERN CA OFFSHORE WATERS
WILL ARRIVE FROM THE WEST NORTHWEST DIRECTION THROUGH SATURDAY
NIGHT. THE SOUTH SWELL WILL CONTINUE TO SUBSIDE WHILE LINGERING
THROUGH SATURDAY. A 982 MB 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).
HIGH RIP CURRENT RISK (SEE LAXSRFLOX).

&&

$$

PUBLIC...SIRARD/KITTELL
AVIATION...SIRARD
MARINE...SMITH
SYNOPSIS...SUKUP

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