014 
FXUS66 KLOX 042104
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
200 PM PDT SUN APR 4 2010

.SYNOPSIS...

A COLD FRONT WILL SWEEP ACROSS THE AREA TONIGHT...AND RAIN IS LIKELY 
EVERYWHERE THROUGH MONDAY MORNING. DRY AND WARM OFFSHORE FLOW IS 
EXPECTED TUESDAY THROUGH THURSDAY. ON FRIDAY THROUGH THE WEEKEND... 
THE RIDGE BREAKS DOWN AND A TROUGH MOVES OVER THE AREA...WITH 
SIGNIFICANT COOLING EXPECTED.

&&

.SHORT TERM (TODAY-WED)...PARTLY TO MOSTLY CLOUDY AFTERNOON TODAY 
DUE TO STRATOCU LAYER AND SOME HIGH CLOUDS MOVING ACROSS THE AREA...
AHEAD OF UPCOMING FRONTAL SYSTEM. WESTERLY WINDS ARE STARTING TO 
INCREASE ACROSS THE MOUNTAINS AND ANTELOPE VALLEY THIS AFTERNOON. 

FORECAST WISE...12Z GFS AND WRF ARE IN VERY GOOD AGREEMENT...AND
INDICATE THE PASSAGE OF A DECENT FRONTAL SYSTEM TONIGHT AND MONDAY.
AT THIS TIME...MODERATE RAINFALL IS EXPECTED THIS EVENING AND EARLY 
MONDAY MORNING ACROSS SLO/SBA COUNTIES...THEN MONDAY MORNING ACROSS
VTU/LAX COUNTIES...WITH SOME ISOLATED SHOWERS REMAINING OVER 
INTERIOR SECTIONS THROUGH MONDAY EVENING DUE TO NORTHERLY FLOW 
BEHIND THE FRONT. THE FRONTAL PASSAGE WILL BE ACCOMPANIED BY A 120+ 
KNOT JET FORECAST TO MOVE SBA COUNTY TONIGHT. JET DYNAMICS SHOULD
HELP TO ENHANCE RAINFALL ALONG THE FRONT...ESPECIALLY OVER NORTHERN 
SECTIONS. AT THIS TIME...EXPECT 0.25" TO 0.75" WITH LOCAL AMOUNTS
TO AROUND 1.00" OVER SLO/SBA COUNTIES...WITH A LITTLE LESS OVER 
VTU/LAX COUNTIES (GENERALLY 0.20" TO 0.50" WITH LOCAL AMOUNTS AROUND
0.75"). WITH FORECAST CONFIDENCE HIGH...HAVE UPGRADED POPS TO 
CATEGORICAL LEVELS FOR ALL AREAS TONIGHT. SNOW LEVELS ARE EXPECTED
TO DROP TO AROUND 4500 TO 5000 FEET TONIGHT...WHICH SHOULD PRODUCE
3-6 INCHES OF NEW SNOWFALL AT THE HIGHER ELEVATIONS. 12Z MODELS 
INDICATED SOME DECENT INSTABILITY THIS EVENING AND OVERNIGHT OVER 
NORTHERN SECTIONS...SO HAVE INCLUDED SLIGHT CHANCE THUNDERSTORMS FOR 
SLO COUNTY AND NORTHERN SECTIONS OF SBA COUNTY. AT THIS TIME...DO 
NOT ANTICIPATE RAINFALL RATES TO REACH LEVELS THAT WOULD CAUSE ANY
PROBLEMS FOR THE BURN AREAS.

ALONG WITH THE RAINFALL...THE FRONT SHOULD PACK SOME PRETTY STRONG
WINDS...ESPECIALLY WITH THE JET MOVING OVERHEAD. WARNING LEVEL GUSTS 
ARE ANTICIPATED ACROSS ALL MOUNTAIN ZONES AND ACROSS SECTIONS OF 
THE ANTELOPE VALLEY. WILL ISSUE HIGH WIND WARNINGS FOR SLO/SBA 
COUNTY MOUNTAINS AND THE ANTELOPE VALLEY. FOR THE VTU/LAX MOUNTAINS
WILL ISSUE WINTER STORM WARNING FOR THE COMBO OF STRONG WIND GUSTS 
AND EXPECTED ADVISORY LEVEL SNOW AMOUNTS. FUTURE SHIFTS WILL ALSO
HAVE TO CONSIDER THE POSSIBILITY OF WIND ADVISORIES FOR COASTAL AND
VALLEY AREAS TONIGHT.  

ON TUESDAY...A UPPER RIDGE BEGINS TO BUILD OVER THE EASTERN PACIFIC
AS NORTHERLY SURFACE FLOW INCREASES. SO...TUESDAY SHOULD BE DRY AND
WARMER WITH NORTHERLY WINDS IN THE USUAL PLACES (SANTA YNEZ RANGE 
AND THE I-5 CORRIDOR). IN FACT...WOULD NOT BE SURPRISED TO SEE SOME
ADVISORY LEVEL WINDS IN THESE AREAS.

FOR WEDNESDAY...THE SURFACE TURNS NORTHEAST AS THE UPPER RIDGE MOVES 
OVER THE AREA. THIS WILL SET THE STAGE FOR A DECENT NORTHEAST WIND
EVENT. ADVISORY LEVEL WINDS ARE LIKELY ACROSS VTU/LAX COUNTIES 
TUESDAY NIGHT/WEDNESDAY. WITH THE NORTHEAST FLOW...TEMPS WEST OF
THE MOUNTAINS WILL WARM UP NOTICEABLY WITH TEMPS IN THE MID 70S TO
MID 80S. INTERIOR SECTIONS WILL BE COOLER DUE TO SOME COLD ADVECTION.

.LONG TERM (THU-SUN)...THURSDAY SHOULD BE VERY SIMILAR TO WEDNESDAY
ALTHOUGH OFFSHORE FLOW WILL BE WEAKER. COASTAL AREAS MAY BE A FEW
DEGREES COOLER DUE TO EARLIER ONSET OF SEA BREEZE..BUT INTERIOR 
SECTIONS WILL BE WARMER DUE TO LESS COLD AIR ADVECTION. 

FOR FRIDAY THROUGH SUNDAY...THE EXTENDED MODELS GRADUALLY DIVERGE 
THROUGH THE PERIOD...BUT ALL INDICATE A COOLING TREND AS UPPER RIDGE 
BREAKS DOWN AND SURFACE FLOW TURNS ONSHORE. THE GFS DOES INDICATE
THE POTENTIAL FOR A SIGNIFICANT STORM ON SUNDAY...BUT THE ECMWF AND
CANADIAN DO NOT INDICATE SUCH A SCENARIO. HOWEVER...THIS WILL HAVE
TO BE WATCHED CLOSELY THE NEXT FEW DAYS.

&&

.AVIATION...04/1800Z.

MID/UPPER LEVEL TROUGH OF LOW PRESSURE CENTERED UPSTREAM WILL MOVE 
OVER THE AREA. STRONG UPPER LEVEL SOUTHWEST WINDS WILL BECOME STRONG 
WEST NORTHWEST AFTER 05/21Z WHILE MODERATE MID LEVEL WEST SOUTHWEST 
WINDS BECOME MODERATE TO STRONG AFTER 05/06Z THEN MODERATE WEST 
NORTHWEST AFTER 05/21Z. AIR MASS WILL BECOME MOIST AND UNSTABLE 
AFTER 05/00Z THEN MOISTURE WILL DECEASE WITH INCREASING STABILITY 
AFTER 05/15Z. THERE IS A SLIGHT CHANCE OF THUNDERSTORMS IN THE NORTH 
HALF OF THE AREA BETWEEN 05/00-05/12Z. FREEZING LEVEL VARIED FROM 
5KFT NORTH HALF TO AROUND 10KFT SOUTH HALF THIS MORNING...AND WILL 
DESCEND TO AROUND 4KFT IN THE NORTH TO AROUND 5KFT IN THE SOUTH 
AFTER 05/12Z.  

KLAX...IT IS LIKELY CIGS 040 WILL DEVELOP AT TIMES THROUGH THE 
PERIOD. THERE IS A CHANCE CIGS WILL DESCEND TO 030 BY 05/09Z WITH 
RAIN. THERE IS A CHANCE SURFACE WINDS WILL INCREASE 25020G35KT BY 
05/15Z. 

KBUR...IT IT LIKELY CIGS 030 WILL BECOME SCATTERED BY 
04/19Z...OTHERWISE IT IS LIKELY CIGS 040 WILL DEVELOP AT TIMES 
THROUGH THE PERIOD. THERE IS A CHANCE CIGS WILL DESCEND TO 020 BY 
05/09Z WITH RAIN.

VIRTUALLY CERTAIN - 95-100%
VERY LIKELY       - 80-95%
LIKELY            - 60-80%
CHANCE            - 30-60%
VERY UNLIKELY     - 20% OR LESS

***NOTE***
THE ASOS EQUIPMENT AT KBUR...KVNY...KHHR...KCMA...AND KOXR HAS A 
SOFTWARE ERROR THAT MAY LEAD TO INCORRECT CLOUD HEIGHTS WHEN THERE 
ARE TWO OR MORE CLOUD LAYERS PRESENT. OBSERVATIONS AT KBUR WILL BE 
QUALITY CONTROLLED 24 HOURS A DAY...OBSERVATIONS AT KVNY WILL BE 
QUALITY CONTROLLED FROM 13Z-07Z...OBSERVATIONS AT KOXR WILL BE 
QUALITY CONTROLLED FROM 15Z-05Z. TAFS FOR KVNY AND KOXR WILL NOT BE 
AMENDED FOR CIGS DURING THE TIME THE OBSERVATIONS ARE NOT MONITORED 
AND THERE ARE TWO OR MORE CLOUD LAYERS PRESENT.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING (SEE LAXWSWLOX).
HIGH WIND WARNING (SEE LAXNPWLOX).
WIND ADVISORY (SEE LAXNPWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
HIGH SURF ADVISORY (SEE LAXCFWLOX).
HIGH RIP CURRENT (SEE LAXSRFLOX)
SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).

&&

$$

PUBLIC...THOMPSON
AVIATION...30
SYNOPSIS...MEIER

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