Area Forecast Discussion
Issued by NWS San Diego, CA

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000
FXUS66 KSGX 210440
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
840 PM PST SAT DEC 20 2014

.SYNOPSIS...
THE DEEP MOIST LAYER WEST OF THE MOUNTAINS WILL BEGIN TO THIN ON
SUNDAY AS HIGH PRESSURE BUILDS OVER THE EAST PACIFIC. MORE HIGH
CLOUDS WILL SPILL SOUTHEAST ACROSS THE STATE ON SUNDAY...THEN MOSTLY
CLEAR...DRY...AND WARMER THROUGH MIDWEEK AS SURFACE WINDS TURN
OFFSHORE AND BECOME GUSTY ALONG THE COASTAL FOOTHILLS. COOLER ON
CHRISTMAS DAY AS THE RIDGE ALOFT WEAKENS AND ONSHORE FLOW DEVELOPS.
DRY WITH SEASONAL TEMPERATURES FOR THE BALANCE OF THE HOLIDAY
WEEKEND.

&&

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

LAYERS OF CLOUDS WERE WIDESPREAD ACROSS THE REGION AGAIN TODAY IN
NORTHWEST FLOW ALOFT. THE ABUNDANCE OF CLOUDS TODAY WAS REFLECTED IN
THE 0.97 INCH PW VALUE OF THE 00Z MIRAMAR SOUNDING THIS AFTERNOON.
AT 7 PM PST...SURFACE PRESSURE GRADIENTS WERE WEAK OFFSHORE FROM
NV...BUT WERE 1-2 MBS ONSHORE TO THE LOWER DESERTS SUPPORTING LOCAL
WESTERLY WINDS IN THE MOUNTAINS OF 15-25 MPH WITH HIGHER GUSTS.

THE LATEST AVAILABLE GLOBAL MODEL RUNS INDICATE THE DEVELOPMENT OF A
STRONG 594 DM HIGH CENTER NEAR 30N/130W BY SUN EVENING. A RIDGE WILL
EXTEND NE OF THE HIGH ALONG THE WEST COAST BY 12Z TUE...HELPING TO
BUILD A COLD SURFACE HIGH INTO THE GREAT BASIN/NORTHERN ROCKIES. THE
COMBINATION OF FLOW ALOFT AROUND THE STRONG UPPER HIGH AND OFFSHORE
SURFACE PRESSURE GRADIENTS WILL PRODUCE A PERIOD OF GUSTY OFFSHORE
WINDS BELOW THE PASSES AND CANYONS OF SOCAL MON NIGHT/TUE. MUCH
WARMER MON/TUE AFTERNOON AS THE DRY...DOWNSLOPING OFFSHORE FLOW
RAPIDLY WARMS TOWARD THE COAST UNDER CLEAR SKIES. CURRENT
INDICATIONS ARE THAT WINDS COULD REACH HIGH WIND CRITERIA ON TUE
MORNING IN WIND PRONE AREAS. A WATCH MAY BE NEEDED IF LATER MODEL
RUNS CONFIRM.

THE STRONG HIGH OVER THE EASTPAC WILL SUBSIDE LATE WED/THU AS A
SHORT WAVE TROUGH SLIDES EAST ACROSS THE PACNW AND DIGS INTO THE
FOUR CORNERS AREA. ONSHORE FLOW WILL RETURN CHRISTMAS DAY AND MAY
BRING A FEW MARINE CLOUDS WITH IT. THE LATEST ECMWF RUN STILL WANTS
TO PRODUCE SOME LIGHT PRECIPITATION OVER SOCAL...MAINLY THU NIGHT...
BUT FOR NOW THE DRY GFS SOLUTION IS FAVORED IN THE CURRENT FORECAST.
COOLER THROUGH THE HOLIDAY WEEKEND...BUT TEMPERATURES SHOULD BE
CLOSE TO AVERAGE.

.ASTRONOMY...
ASTRONOMICAL WINTER WILL OFFICIALLY BEGIN AT 3:03 PM ON SUNDAY WITH
THE NORTHERN HEMISPHERE TILTED AT ITS GREATEST ANGLE AWAY FROM THE
DIRECT RAYS OF THE SUN.

&&

.AVIATION...
210430Z...COAST/VALLEYS...AREAS OF SCT-BKN LOW CLOUDS WITH BASES
2500-3500 FEET MSL WILL AFFECT COASTAL TAF SITES AT TIMES THROUGH
15Z SUN. LOW CLOUDS BECOME SCT AFT 15Z SUN.

MTNS/DESERTS...HIGHER TERRAIN OBSCURED WITH FOG REDUCING VIS WHERE
CLOUDS AND TERRAIN INTERSECT. OTHERWISE...SCT-BKN CLOUDS AOA 12000
FEET THROUGH SUN.

&&

.MARINE...
830 PM...COMBINED SEAS TO 9 FEET IS POSSIBLE OVER PORTIONS OF THE
OUTER COASTAL WATERS LATE TONIGHT INTO SUNDAY MORNING. OTHERWISE NO
HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH WEDNESDAY.

&&

.BEACHES...
830 PM...A LARGE...LONG PERIOD WEST-NORTHWEST SWELL WILL CREATE
ELEVATED SURF AND STRONGER RIP CURRENTS THROUGH EARLY SUNDAY. IN
ADDITION...MORNING HIGH TIDES AROUND 7 FEET COULD CONTRIBUTE TO
MINOR TIDAL OVERFLOW THROUGH TUESDAY. SEE THE BEACH HAZARD STATEMENT
FOR DETAILS...LAXCFWSGX.

&&

.FIRE WEATHER...
OFFSHORE FLOW AND DRIER CONDITIONS WILL DEVELOP ACROSS SOUTHERN
CALIFORNIA FOR SUNDAY THROUGH TUESDAY.  ALTHOUGH THE OFFSHORE
GRADIENTS WILL BE RELATIVELY WEAK ON SUNDAY AND MONDAY...LOCALLY
GUSTY NORTH TO NORTHEAST WINDS WILL BE POSSIBLE.  THESE NORTH TO
NORTHEAST WINDS WILL LIKELY INCREASE ON MONDAY EVENING THOUGH...WITH
MODERATE TO STRONG WINDS POSSIBLE LATE MONDAY NIGHT AND INTO
TUESDAY.  THE FAVORED PASSES AND CANYONS AS WELL AS COASTAL SLOPES
MAY SEE GUSTS RANGING BETWEEN 65 AND 75 MPH.  HUMIDITY VALUES WILL
GRADUALLY LOWER THESE DAYS AS WELL...FALLING TO BETWEEN 10 AND 20
PERCENT BY TUESDAY.  HOWEVER...INCREASED FUEL MOISTURE DUE TO RECENT
RAINS WILL LIMIT THE POTENTIAL FIRE DANGER.

&&

.SKYWARN...
SKYWARN ACTIVATION WILL NOT BE NEEDED ON SUNDAY.

&&

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

PZ...NONE.

&&

$$

PUBLIC...JAD
FIRE WEATHER...PALMER
AVIATION/MARINE...PG





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