000
FXUS66 KSGX 130407
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
907 PM PDT SUN MAY 12 2013

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVER CALIFORNIA THROUGH MONDAY...WITH
ANOTHER HOT DAY SHAPING UP INLAND. A FEW RECORDS WILL LIKELY FALL
AGAIN TOMORROW. CLOSE TO THE COAST...A VERY SHALLOW MARINE LAYER
WILL LINGER...MODERATING TEMPERATURES AND SUPPORTING AREAS OF LOW
CLOUDS AND FOG. A GRADUAL COOLING TREND WILL BEGIN ON TUESDAY AS THE
MARINE LAYER DEEPENS AND THE RIDGE FLATTENS. AN UPPER-LEVEL TROUGH
WILL THEN DEVELOP ALONG THE WEST COAST AND MOVE INLAND FOR THE
REMAINDER OF THE WEEK...BRINGING MUCH COOLER CONDITIONS...A DEEPER
MARINE LAYER...AND GUSTY WEST WINDS IN THE MOUNTAINS AND DESERTS.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

TEMPERATURES SOARED PAST THE CENTURY MARK OVER THE INLAND EMPIRE AND
THE LOWER DESERTS THIS AFTERNOON. INLAND SAN DIEGO AND ORANGE
COUNTIES WERE QUITE WARM AS WELL...WITH WIDESPREAD TEMPS IN THE 90S.
A SHALLOW MARINE LAYER KEPT THE IMMEDIATE COAST COOLER WHERE TEMPS
REMAINED IN THE 70S AND PATCHES OF FOG LINGERED. A PRONOUNCED
CLEARING TREND DEVELOPED OVER THE COASTAL WATERS DURING THE EVENING
ON SATELLITE IMAGERY. THIS APPEARS TO BE ASSOCIATED WITH A STRONGER
NW WIND FIELD FORMING JUST ABOVE THE SURFACE. THE WIND WILL KEEP THE
LAYER MIXED UNTIL LATER TONIGHT. AFTER THE WINDS WEAKEN...THE LOW
STRATUS/FOG WILL HAVE A CHANCE TO REFORM.

ONLY CHANGES TO THE FORECAST PERTAIN TO THE EXTENT AND ONSET OF THE
FOG. UNCERTAINTY HAS INCREASED DUE TO MIXING OUT OF THE MAJORITY OF
THE FOG/STRATUS LAYER OVER THE CA BIGHT. PATCHES REMAIN...AND SOME
REDEVELOPMENT IS EXPECTED NEARSHORE LATER TONIGHT...BUT LIKELY TO BE
MUCH LESS EXTENSIVE THAN LAST NIGHT. LOCAL MODELS/MOS GUIDANCE DO
NOT SUPPORT FOG REDEVELOPMENT. OFFSHORE SFC PRESSURE GRADIENT TRENDS
AND DRAINAGE LATER TONIGHT DO NOT SUPPORT ANY MARINE LAYER ADVANCE
ONSHORE...ESPECIALLY IN ORANGE COUNTY...SO THAT AREA HAS BEEN
REMOVED FROM THE ADVISORY AND WILL MONITOR THROUGH THE NIGHT.

STRONG HIGH PRESSURE ALOFT WILL BE WITH US ONE MORE DAY...THEN
WEAKEN AS A WEAK TROUGH APPROACHES FROM THE WEST ON TUE. THIS WILL
BE FOLLOWED BY A MORE ZONAL FLOW PATTERN THROUGH MID WEEK BEFORE A
MORE BROAD UPPER-LEVEL TROUGH DEVELOPS ALONG THE WEST COAST FRI.
SURFACE LOW PRESSURE WILL BE STRENGTHENING OVER THE INTERIOR WEST
THROUGH MID WEEK IN RESPONSE TO THIS PATTERN CHANGE...DRIVING
STRONGER ONSHORE FLOW AND A COOLING TREND THROUGH THE END OF THE
WEEK.

MAIN WEATHER ISSUE AGAIN THIS EVENING IS THE DEPTH OF THE MARINE
LAYER AND ASSOCIATED FOG. THE 00Z MIRAMAR SOUNDING INDICATED THAT
THE WARM AIR HAD MIXED DOWN TO THE SURFACE. IT IS UNCLEAR HOW LONG
IT WILL TAKE THE LAYER TO REFORM...BUT WHAT EVER DOES IS LIKELY TO
BE MORE LIMITED AND UNLIKELY TO SPREAD VERY FAR INLAND. A DENSE FOG
ADVISORY REMAINS IN EFFECT FOR THE IMMEDIATE COASTAL STRIP OF SAN
DIEGO COUNTY AGAIN OVERNIGHT. PLEASE SEE LAXNPWSGX.

SEVERAL RECORD HIGH TEMPERATURES WERE SET THIS AFTERNOON...AND A FEW
MORE MAY FALL AGAIN TOMORROW INLAND. COASTAL AREAS WILL LIKELY
REMAIN MODERATED BY THE MARINE AIR...AND SOME INCREASE IN THE SEA
BREEZE IS EXPECTED LATER IN THE DAY AS ONSHORE SURFACE PRESSURE
GRADIENTS BUILD. THE ONSHORE FLOW WILL BE STRONGER ON TUE AS WE COME
UNDER THE INFLUENCE OF THE UPPER-LEVEL TROUGH. COASTAL AREAS WILL BE
CONSIDERABLY COOLER...AND THE COOLING WILL SPREAD INLAND THROUGH
WED. MAX TEMPS SHOULD BE CLOSER TO AVERAGE FOR THE REMAINDER OF THE
WEEK.

SOME WARMING IS EXPECTED LATER NEXT WEEKEND INTO NEXT WEEK AS THE
UPPER-LEVEL TROUGH SLIDES EAST AND HEIGHTS/THICKNESS REBUILD.
OTHERWISE CONTINUED FAIR AND DRY WITH PERIODS OF MARINE LAYER
CLOUDS.

&&

.AVIATION...
130300Z...COAST...LOW CLOUDS/FG WILL DEVELOP ALONG THE COAST THIS
EVENING...THEN PUSH A FEW MILES INLAND BY MID MON MORNING. BASES
WILL RANGE FROM 200-500 FT MSL...WITH TOPS NEAR 1000 FT MSL. VIS AOB
1 SM IS EXPECTED WHERE STRATUS MEETS HIGHER TERRAIN. LOW CLOUDS WILL
RETREAT TO THE BEACHES AROUND 16 UTC MON MORNING...THEN REDEVELOP
ALONG THE COAST AGAIN MON EVENING. VFR CONDS ARE FORECAST LATE MON
MORNING THROUGH MON AFTN.

VALLEYS/MTNS/DESERTS...FG MAY REACH THE FAR WESTERN PORTIONS OF THE
VALLEYS BY MID MON MORNING...THEN CLEAR BY 16 UTC MON MORNING. VIS
AOB 1 SM WILL BE POSSIBLE WHERE FG DEVELOPS.
OTHERWISE...UNRESTRICTED VIS WITH MOSTLY CLEAR SKIES THROUGH MON
EVENING.

&&

.MARINE...
A SHALLOW MARINE LAYER WILL CREATE AREAS OF DENSE FOG OVER THE
COASTAL WATERS THROUGH TUESDAY MORNING. VISIBILITY COULD DROP AS LOW
AS ONE-QUARTER MILE OR LESS AT TIMES.
&&

.FIRE WEATHER...
VERY HOT AND DRY CONDITIONS WILL PREVAIL ACROSS THE INLAND AREAS
AGAIN ON MONDAY...WITH DAYTIME HUMIDITY VALUES FALLING BELOW 15
PERCENT AFTER WIDESPREAD POOR TO MODERATE RECOVERIES TONIGHT.
HOWEVER...THE WINDS WILL REMAIN RELATIVELY LIGHT AND TERRAIN
DRIVEN...WITH WEAK ONSHORE WINDS DURING THE AFTERNOON.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...DENSE FOG ADVISORY TONIGHT THROUGH 9 AM PDT MONDAY FOR
     THE ORANGE COUNTY COASTAL AREAS...SAN DIEGO COUNTY COASTAL
     AREAS.

PZ...NONE.

&&

$$

PUBLIC...JAD
FIRE...PALMER
AVIATION/MARINE...JJT