Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 200515 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1015 PM PDT TUE AUG 19 2014

...UPDATED AVIATION DISCUSSION...

.SYNOPSIS...

A LOW PRESSURE SYSTEM WILL MOVE ACROSS THE REGION AND INCREASE
THE NIGHT THROUGH MORNING CLOUDS AND FOG THROUGH SATURDAY. THE
MOIST AIR MASS WILL BRING LOCAL DRIZZLE...AND A SLIGHT CHANCE OF
SHOWERS OR THUNDERSTORMS TO THE SOUTHLAND THROUGH THURSDAY. A
HIGH PRESSURE SYSTEM WILL LIKELY ESTABLISH FOR EARLY NEXT WEEK
WITH ABOVE NORMAL TEMPERATURES.

&&

.UPDATE...

THE WATER VAPOR IMAGERY INDICATES A LOW PRESSURE SYSTEM
CONTINUING TO DIG SOUTH OFF THE SOUTHERN CALIFORNIA COAST THIS
EVENING. SOME CONVECTION HAS FIRED OFF TO THE SOUTH AND EAST OF
THE AREA...BUT THE AREA HAS REMAINED DRY. A DEEP MARINE LAYER
SHOULD BRING AN EXTENSIVE MARINE LAYER INDUCED STRATUS FIELD TO
THE MUCH OF THE COASTAL AND VALLEY AREAS LATER TONIGHT. THE LATEST
FOG PRODUCT IS GIVING INDICATIONS OF A RAPID FILLING-IN OF
STRATUS LATE THIS EVENING. DRIZZLE OR LIGHT SHOWERS FROM THE
STRATUS DECK CANNOT BE RULED AS THE INSTABILITY OF THE TROUGH
APPROACHES AND RAPID DEEPENING OF THE MARINE LAYER TAKES PLACE.

THE LATEST NAM-WRF AND RAP SOLUTIONS SUGGEST THE TIMING OF THE
CONVECTION OCCURRING A LITTLE EARLIER THAN PREVIOUSLY THOUGHT.
BOTH 00Z NAM-WRF SOLUTIONS AND THE LATEST RAP SOLUTIONS SUGGEST AN
AREA OF NEGATIVE LIFTED INDEX VALUES FORMING OVER THE SOUTHERN
COASTAL WATERS LATE TONIGHT WHEN THE COLDEST AIR ALOFT WITH THE
TROUGH MOVES INTO THE REGION. AN AREA OF DIFLUENCE FLOW ALOFT
SHOULD DEVELOP AHEAD OF THE MAIN VORTICITY MAXIMUM AND SHOULD
ALLOW FOR SHOWERS AND THUNDERSTORMS TO FIRE...EVEN ABOVE THE
MARINE LAYER STRATUS DECK. POPS HAVE BEEN BUMPED FOR THE COASTAL
WATERS AND THE LOS ANGELES COUNTY COAST AFTER MIDNIGHT TONIGHT.

THE LATEST NAM-WRF SOLUTIONS CONTINUE TO SLOW THE TROUGH...BEING
LESS PROGRESSIVE RELATIVE TO THE GFS AND ECMWF SOLUTIONS. IF NAM-
WRF SOLUTIONS PLAY OUT...POPS AND WEATHER MAY NEED TO BE ADDED FOR
THURSDAY AS THE TROUGH AXIS LINGERS OVER THE AREA. WHILE THE NAM-
WRF SOLUTIONS REMAIN THE OUTLIER...THE TROUGH IS CUT-OFF FROM THE
FLOW AND TYPICALLY MODEL PERFORMANCE WITH CLOSED AND CUT-OFF LOWS
WOULD FAVOR NAM-WRF SOLUTIONS FOR SOUTHERN CALIFORNIA AND
SOUTHWESTERN UNITED STATES. WITH THE NWS WEATHER PREDICTION CENTER
MENTIONING SREF SOLUTIONS FAVORING RETROGRESSION OF THE
TROUGH...IT IS POSSIBLE THAT THE NAM-WRF SOLUTION MAY NOT BE TOO
FAR OFF. THE NEXT SHIFT WILL BE BRIEFED ABOUT POPS AND WEATHER
POSSIBILITIES FOR THURSDAY.

&&

.PREV DISCUSSION...

SHORT TERM...THE UPPER LOW MOVES SOUTHEAST TO THE HIGH DESERTS
ON THURSDAY. THE LAST BIT OF INSTABILITY AND MOISTURE WILL BE OVER
THE EASTERN SAN GABRIEL MOUNTAINS FOR A CONTINUED SLIGHT CHANCE OF
THUNDERSTORMS. A SHALLOWER MARINE LAYER IS LIKELY ON THURSDAY
MORNING BUT WILL STILL SEE LOW CLOUDS FOR COASTS AND NEARBY
VALLEYS TO START THE DAY. BY FRIDAY MORNING THE MARINE LAYER
SHRINKS EVEN MORE AND MAY ONLY SEE PATCHY CLOUDS SOUTH OF PT
CONCEPTION. TEMPERATURES WILL START TO REBOUND LATE IN THE WEEK
BUT A LARGE SCALE UPPER TROUGH ACROSS MOST OF THE WEST WILL SLOW
ANY SIGNIFICANT WARMING UNTIL LATER IN THE WEEKEND.

LONG TERM...HIGH PRESSURE SLOWLY BUILDS ACROSS THE SOUTHWEST OVER
THE WEEKEND WITH TEMPERATURES WARMING AND THE MARINE LAYER
BECOMING LESS OF AN ISSUE FOR COASTAL AREAS. VERY LITTLE
SIGNIFICANT WEATHER ISSUES THROUGH TUESDAY. REMNANT MOISTURE FROM
TWO TROPICAL SYSTEMS (LOWELL AND KARINA) COULD GET PULLED
NORTHWARD CLOSER TO SOUTHERN CALI BY MONDAY OR TUESDAY. WOULD ONLY
EXPECT SOME MID TO HIGH LEVEL CLOUDS FROM THESE SYSTEMS AT BEST
WITH LITTLE EFFECT ON TEMPERATURES.

&&

.AVIATION...20/0515Z...

OVERALL...MODERATE CONFIDENCE IN 06Z TAF PACKAGE. WITH UPPER LOW
WOBBLING NEAR THE AREA...MARINE INVERSION SHOULD DEEPEN AND MVFR
CIGS SHOULD IMPACT ALL COASTAL/VALLEY TAF SITES OVERNIGHT. COULD BE
SLOW TO CLEAR WEDNESDAY AFTERNOON SOUTH OF POINT CONCEPTION...BUT
THE PREVIOUSLY MENTIONED UPPER LOW COULD MIX OUT THE MVFR CIGS
EARLIER/BETTER THAN ANTICIPATED. WITH THE DEEPENING INVERSION...THERE
COULD BE SOME PATCHY DRIZZLE WEST OF THE MOUNTAINS OVERNIGHT.

OTHER ISSUE TO WATCH WILL BE SLIGHT CHANCE OF TSTMS IMPACTING MAINLY
LOS ANGELES COUNTY LATE TONIGHT AND WEDNESDAY. AT THIS TIME...WILL
MENTION A VCTS REMARK WEDNESDAY AFTERNOON FOR KPMD/KWJF. HOWEVER
DEPENDING ON HOW THINGS DEVELOP LATE TONIGHT...THERE IS THE
POTENTIAL FOR TSTMS TO IMPACT KLAX/KLGB/KBUR/KVNY. WILL WATCH THE
SITUATION CLOSELY.

KLAX...MODERATE CONFIDENCE IN 06Z TAF. HIGH CONFIDENCE IN MVFR CIGS
THROUGH WEDNESDAY MORNING...WITH LOW CONFIDENCE IN CLEARING
WEDNESDAY AFTERNOON. THERE IS A 10% CHANCE OF TSTMS IMPACTING THE
AIRFIELD LATE TONIGHT/WEDNESDAY.

KBUR...MODERATE CONFIDENCE IN 06Z TAF. HIGH CONFIDENCE IN MVFR CIGS
THROUGH WEDNESDAY MORNING. LOW CONFIDENCE IN CURRENT FORECAST/TIMING
OF CLEARING WEDNESDAY AFTERNOON. THERE IS A 10% CHANCE OF TSTMS
IMPACTING THE AIRFIELD LATE TONIGHT/WEDNESDAY.

&&

.MARINE...19/900 PM.

TIMING FOR CHANCES FOR SHOWERS AND THUNDERSTORMS HAS BEEN BUMPED
TO AN EARLIER TIME FRAME. SHOWERS AND THUNDERSTORMS COULD DEVELOP
ACROSS THE SOUTHERN WATERS AFTER MIDNIGHT TONIGHT. GUSTY AND
ERRATIC WINDS...CHOPPY SEAS...SMALL HAIL...AND DANGEROUS CLOUD-TO-
OCEAN LIGHTNING ARE POSSIBLE AFTER MIDNIGHT TONIGHT AND THROUGH
WEDNESDAY MORNING. OTHERWISE...WINDS AND SEAS WILL REMAIN BELOW
SMALL CRAFT ADVISORY LEVELS.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
MARINE WEATHER STATEMENT (SEE LAXMWWLOX).

&&

$$

PUBLIC...HALL/BOLDT
AVIATION...GOMBERG
MARINE...HALL
SYNOPSIS...SETO/HALL

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