Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 310455 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
955 PM PDT THU JUL 30 2015

UPDATED AVIATION AND MARINE SECTIONS

.SYNOPSIS...THUNDERSTORM ACTIVITY WILL WIND DOWN THIS EVENING.
HOWEVER THERE WILL BE A CHANCE OF THUNDERSTORMS FOR THE INTERIOR
MOUNTAINS AND DESERTS AGAIN ON FRIDAY. THE THUNDERSTORM THREAT WILL
BE CONFINED TO THE LOS ANGELES AND VENTURA COUNTY MOUNTAINS AND
ADJACENT DESERTS OVER THE WEEKEND. BY MONDAY...STABILIZING SOUTHWEST
FLOW ALOFT WILL END THE THREAT OF THUNDERSTORMS.

&&

.SHORT TERM (TODAY-SUN)...VERY ACTIVE THUNDERSTORM DAY WITH SEVERAL
FLASH FLOOD WARNINGS ISSUED ACROSS THE MOUNTAINS AND ANTELOPE
VALLEY. THIS DUE TO COMBINATION OF UPPER LEVEL WAVE INTERACTING WITH
DEEP MONSOONAL MOISTURE ACROSS THE REGION. ESRL GPS PRECIPITABLE
WATER SENSORS SHOWED A LARGE AREA OF PW VALUES BETWEEN 1.8 AND 2.0
INCHES ACROSS VENTURA AND LOS ANGELES COUNTIES TODAY. DOPPLER RADAR
ESTIMATED RAINFALL RATES LOCALLY GREATER THAN 2 INCHES PER HOUR WITH
SOME OF THE STRONGER THUNDERSTORMS. FLASH FLOODING WAS REPORTED ON
SEVERAL MAJOR ROADWAYS ACROSS THE REGION TODAY...INCLUDING
INTERSTATE 5 AS WELL AS HIGHWAYS 14...33 AND 138. IN ADDITION TO THE
NUMEROUS FLASH FLOOD STORMS...THERE WERE TWO SEVERE THUNDERSTORM
WARNINGS ISSUED FOR LARGE HAIL/STRONG WINDS IN THE MOUNTAINS OF LOS
ANGELES AND VENTURA COUNTIES.

CONVECTIVE ACTIVITY...OVERALL...WAS GRADUALLY BEGINNING TO DIMINISH
THIS EVENING. HOWEVER...THE ATMOSPHERE IS STILL UNSTABLE...PW VALUES
ARE STILL HIGH...AND OCCASIONAL STORMS HAVE PULSED UP...SO HAVE
EXTENDED THE EXISTING FLASH FLOOD WATCH THROUGH 10 PM PDT. WILL
REMOVE ANY POPS FOR COASTAL AND VALLEY AREAS AFTER 10 PM. SLIGHT
CHANCE POPS LOOK REASONABLE FOR INTERIOR SECTIONS OF SLO AND SBA
COUNTY...THE MTNS AND THE ANTELOPE VALLEY THROUGH THE NIGHT...SO
WILL PROBABLY LEAVE THOSE POPS AS IS. DESPITE THE MONSOONAL
PUSH...THE WRF SUGGESTS THAT THERE MAY BE SOME LOW CLOUDS AND FOG
ACROSS THE CENTRAL COAST AND ACROSS COASTAL SECTIONS OF L.A. COUNTY
OVERNIGHT/FRI MORNING. IT APPEARS AS THOUGH ANY STRATUS WILL BE
PATCHY IN NATURE AT WORST.

FOR FRI...THE WRF SHOWS GOOD INSTABILITY ACROSS THE MTNS AND THE
ANTELOPE VALLEY. HOWEVER...THERE WILL NOT BE AS MUCH IN THE
AVAILABLE MOISTURE...WITH PW VALUES DOWN TO ABOUT 1.4-1.5
INCHES...DOWN FROM 2 INCHES TODAY. IN ADDITION...THE WRF SHOWS SOME
DRYING DURING THE AFTERNOON...WITH PW VALUES DROPPING TO BETWEEN 1.0
AND 1.2 BY LATE AFTERNOON. STILL...THE SLIGHT CHANCE OF SHOWERS AND
TSTMS LOOKS REASONABLE FOR THE MTNS...ANTELOPE VALLEY AND THE
INTERIOR VLYS OF SLO AND SBA COUNTIES. MAX TEMPS SHOULD BE DOWN A
BIT IN MOST AREAS ON FRI...THANKS TO INCREASED ONSHORE FLOW AND
SMALL DECREASES IN HEIGHTS/THICKNESSES AND TEMPS AT 850 MB AND
950 MB.

...FROM PREVIOUS DISCUSSION...

THE AREAL COVERAGE OF T-STORMS ON SATURDAY WAS REDUCED TO ONLY HAVE
A SLIGHT CHANCE OF T-STORMS OVER THE VTA/LA MOUNTAINS AND THE
ANTELOPE VALLEY. WITH FLOW ALOFT STARTING TO SHIFT TO THE SW ON
SATURDAY...MOISTURE AND INSTABILITY WILL CONTINUE TO DECREASE...WITH
MOST OF THE INSTABILITY FOCUSED OVER THE VTA/LA MOUNTAINS. THE
DRYING TREND WILL CONTINUE ON SUNDAY AS SW FLOW BECOMES ESTABLISHED
ALOFT...BUT THERE COULD STILL BE ENOUGH LINGERING INSTABILITY TO
WARRANT THE SLIGHT CHANCE OF T-STORMS FOR THE EASTERN SAN GABRIELS
AND ANTELOPE VALLEY.

SLIGHT WARMING TREND MAY BEGIN ON SUNDAY AS THE RIDGE OVER NEW
MEXICO STARTS TO BUILD...RESULTING IN SLIGHT HEIGHT/THICKNESS RISES
OVER SW CALIFORNIA. ALSO INTRODUCED SOME LOW CLOUDS IN SOUTHERN LA
COUNTY ON SUNDAY MORNING AS THE MARINE LAYER MAY START TO RE-DEVELOP
WITH SW FLOW ALOFT DUE TO A WEAK UPPER-LOW OFF THE COAST.

.LONG TERM (MON-THU)...

OVERALL NOT A VERY EXCITING WEATHER PATTERN NEXT WEEK WITH A
PERSISTENT RIDGE OVER THE INTERIOR WESTERN U.S. AND A TROUGH OFF THE
WEST COAST. THE TROUGH WILL BRING A BETTER CHANCE FOR MARINE LAYER
STRATUS FOR MOST COASTAL AREAS NEXT WEEK. NO SIGNIFICANT TEMPERATURE
TRENDS IN THE FORECAST NEXT WEEK AS THERE IS SOME SLIGHT
DISAGREEMENT IN THE MODELS. GFS BUILDS THE RIDGE MORE AGGRESSIVELY...
WHICH WOULD RESULT IN A WARMING TREND FOR INTERIOR AREAS...WHILE THE
ECMWF KEEPS THE RIDGE RELATIVELY FLAT. CURRENT FORECAST HAS
TEMPERATURES GENERALLY NEAR NORMAL NEXT WEEK.

&&

.AVIATION...31/0455Z...

AT 0314Z...THE MARINE LAYER DEPTH AT KLAX WAS 900 FEET. THE TOP OF
THE INVERSION WAS LOCATED AT 2500 FEET WITH A TEMPERATURE OF 25C.

MONSOONAL MOISTURE HAS DISRUPTED THE LOW CLOUD FIELD FOR THE TIME
BEING. EXPECT STRATUS TO DEVELOP OVERNIGHT AND LINGER THROUGH MID OR
LATE MORNING FRI ACROSS THE CENTRAL COAST...AND POSSIBLY ACROSS
COASTAL SECTIONS OF L.A. COUNTY. CONDS SHOULD BE MOSTLY IFR...EXCEPT
LOW MVFR ACROSS L.A. COUNTY.

KLAX...LOW CONFIDENCE IN THE 06Z TAF. THERE IS A 40 PERCENT CHANCE
THAT CONDS WILL REMAIN VFR OVERNIGHT/FRI MORNING. IF CIGS
DEVELOP...THERE IS A 30 PERCENT CHANCE THEY WILL BE IN THE IFR
CATEGORY RATHER THAN THE CURRENT FORECAST OF LOW MVFR.

KBUR...HIGH CONFIDENCE IN THE 06Z TAF WITH VFR CONDS EXPECTED
THROUGH THE PD.

&&

.MARINE...30/955 PM. LOCAL SCA GUSTS THIS EVENING SHOULD DIMINISH
AFTER MIDNIGHT. HIGH CONFIDENCE THAT CONDS WILL REMAIN BELOW SCA
LEVELS ACROSS THE INNER WATERS AND SBA CHANNEL THROUGH THE WEEKEND.
ACROSS THE OUTER WATERS...THERE IS A 30 PERCENT CHANCE THAT SCA
CONDS WILL BECOME WIDESPREAD ENOUGH TO REQUIRE ADVISORIES DURING THE
AFTERNOON AND EVENING HOURS FRI AND SAT...MAINLY ACROSS THE SOUTHERN
TWO THIRDS. SCA CONDS WILL BECOME MORE LIKELY ACROSS THE OUTER
WATERS SAT NIGHT OR SUN.

&&

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

&&

$$

PUBLIC...SUKUP/GOMBERG/BRUNO
AVIATION/MARINE...DB
SYNOPSIS...MUNROE/DB

WWW.WEATHER.GOV/LOSANGELES



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