Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 180400
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
900 PM PDT WED SEP 17 2014

.SYNOPSIS...
A LOW PRESSURE SYSTEM APPROACHING FROM THE NORTHWEST WILL BRING
COOLER WEATHER AND LOWER HUMIDITIES THURSDAY AND FRIDAY. THE MARINE
LAYER WILL RETURN AND MAY BE DEEP ENOUGH FOR PATCHY DRIZZLE WEST
OF THE MOUNTAINS FRIDAY MORNING. STRONG ONSHORE FLOW WILL BRING
GUSTY WEST WINDS TO THE MOUNTAINS AND DESERTS THURSDAY AFTERNOON AND
EVENING. ISOLATED THUNDERSTORMS MAY FORM OVER THE MOUNTAINS SATURDAY
AFTERNOON AS THE TROUGH MOVES ACROSS SOUTHERN CALIFORNIA. DRY AND
WARMER EARLY NEXT WEEK WITH HIGH PRESSURE BUILDING ALOFT.

&&

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

SHOWERS AND THUNDERSTORMS WERE CONFINED TO THE MOUNTAINS AND HIGH
DESERTS TODAY. VOLCAN MOUNTAIN WAS UNDERNEATH ONE OF THE STRONGEST
CELLS THIS AFTERNOON AND RECORDED 0.54" OF RAIN. A 24 HOUR PRECIP
SUMMARY IS HEADLINED ON OUR WEBSITE...AS IS A MAP WITH 48 HOURS RAIN
TOTALS. THE ATMOSPHERE STABILIZED LATE IN THE AFTERNOON WITH WARMING
ALOFT AND A CAPPING CAPPING INVERSION NEAR 15000 FEET AS SEEN ON THE
00Z SOUNDING. 500 MB NVA ALSO SUPPRESSED THE CONVECTIVE POTENTIAL.

THE HEAT ABATED TODAY...ALBEIT SLIGHTLY...WITH TEMPERATURES WEST OF
THE MOUNTAINS 4-8 DEGREES LOWER THAN YESTERDAY. WHILE IT WAS
"COOLER" IN A RELATIVE SENSE...IT WAS STILL HOT WITH MAX TEMPS IN
THE 90S AND LOW 100S...BEACH COMMUNITIES EXCEPTED. THE NATIONS HOT
SPOTS WERE PALM SPRINGS AND THERMAL WITH A HIGH OF 103 AT BOTH
SITES.

COOLER AND LESS HUMID THURSDAY AND FRIDAY WITH INCREASING ONSHORE
FLOW AS A DEEP TROUGH OFF THE NORCAL COAST MOVES SOUTHEAST. THE
TROUGH WILL ALSO GENERATE SOME STRONGER ONSHORE PRESSURE GRADIENTS
AND RESULT IN STRONGER WEST WINDS IN THE MOUNTAINS AND DESERTS
THURSDAY AFTERNOON AND EVENING WITH GUSTS OF 40-45 MPH. THE MARINE
LAYER WILL DEEPEN WITH NIGHT AND MORNING CLOUDS SPREADING DEEP INTO
THE VALLEYS THURSDAY NIGHT FOR POSSIBLE DRIZZLE FRIDAY MORNING.

ON FRIDAY EVENING THE TROUGH MORPHS INTO A CLOSED LOW OVER PT
CONCEPTION. BOTH THE GFS AND ECMWF TRACK A VORTICITY CENTER
ACROSS SOCAL SATURDAY AFTERNOON ALONG WITH A WEAK SPEED MAX ALOFT.
500 MB TEMPS FALL TO AROUND -11C AND LI`S FALL TO NEAR 0 SATURDAY
AFTERNOON. A MODEST SURGE OF MOISTURE FROM THE SOUTHEAST MAY BE
DRAWN INTO THE SYSTEM IN LOW LEVEL SOUTHEAST FLOW AHEAD OF THE
TROUGH. THE AIRMASS IS FORECAST TO ONLY BECOME MARGINALLY
UNSTABLE...BUT FEEL THE DAYTIME HEATING COMBINED WITH COOLING ALOFT
IS ENOUGH TO WARRANT A SLIGHT CHANCE FOR SHOWERS OR THUNDERSTORMS IN
THE MTNS SATURDAY AFTERNOON/EVENING.

THE TROUGH DRIFTS EAST SUNDAY AND IS FOLLOWED BY WEAK RIDGING ALOFT
MONDAY AND TUESDAY FOR WARMER DAYS AND A SHALLOWER MARINE LAYER.

&&

.AVIATION...
180330Z...COAST/VALLEYS...MOSTLY CLEAR SKIES WILL PREVAIL THROUGH
10Z. SOME BKN STRATUS COULD DEVELOP AT COASTAL AIRPORTS BETWEEN 10Z
AND 14Z THU...BUT CONFIDENCE IS FAIRLY LOW. BASES WILL MOSTLY BE
BETWEEN 1000 AND 1500 FT MSL WITH TOPS 1500 TO 2000 FT MSL. MOST VIS
WILL REMAIN ABOVE 5 MI TONIGHT/THU. SCT WITH POSSIBLE LOCAL BKN
STRATUS IS LIKELY AFTER 17Z THU...WITH STRATUS CHANCES GREATER THU
EVENING WITH BASES MOSTLY ABOVE 2000 FT MSL.

MOUNTAINS/DESERTS...SCT REMNANT CLOUDS AT/ABOVE 10000 FT MSL WILL
GRADUALLY DISSIPATE BY 06Z. OTHERWISE...MOSTLY CLEAR SKIES WITH
UNRESTRICTED VIS WILL PREVAIL THROUGH THU NIGHT.

&&

.MARINE...
830 PM...WIND GUSTS HAVE DECREASED BELOW 20 KNOTS AT SAN CLEMENTE
BASIN BUOY...SO THE SMALL CRAFT ADVISORY WILL BE ALLOWED TO EXPIRE
AT 9 PM. SOME GUSTS TO 20 KT FROM THE WEST/NORTHWEST ARE POSSIBLE
OVER THE OUTER COASTAL WATERS THURSDAY AFTERNOON. OTHERWISE...NO
HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH SUNDAY.

&&

.BEACHES...
830 PM...A LONG PERIOD SOUTHERLY SWELL WILL CONTINUE TO PRODUCE
STRONG RIP AND LONGSHORE CURRENTS...AS WELL AS ELEVATED
SURF...THROUGH THURSDAY. SURF OF 4 TO 6 FEET WITH LOCALLY HIGHER
SETS WILL OCCUR ON EXPOSED SOUTHWEST FACING BEACHES...WITH HIGHEST
SURF IN NORTHERN ORANGE COUNTY. THE SWELL WILL SLOWLY LOWER FRIDAY
AND DIMINISH THE SURF AND RIP CURRENT THREAT. A BEACH HAZARDS
STATEMENT FOR ELEVATED SURF AND STRONG RIP AND LONGSHORE CURRENTS
REMAINS IN EFFECT THROUGH THURSDAY EVENING.

&&

.SKYWARN...
SKYWARN ACTIVATION WILL NOT BE NEEDED THURSDAY.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...BEACH HAZARDS STATEMENT THROUGH THURSDAY EVENING FOR THE
     BEACHES IN THE ORANGE COUNTY COASTAL AREAS...SAN DIEGO COUNTY
     COASTAL AREAS.

PZ...NONE.

&&

$$

PUBLIC...MOEDE
AVIATION/MARINE/BEACHES...MAXWELL






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