FXUS66 KSGX 032054
AFDSGX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
100 PM PST THU DEC 3 2009

.SYNOPSIS...MOSTLY CLEAR SKIES WILL PREVAIL THROUGH FRIDAY NIGHT AS 
HIGH PRESSURE BUILDS. INCREASING OFFSHORE FLOW WILL BRING GUSTY 
WINDS THROUGH AND BELOW MOUNTAIN CANYONS AND PASSES FRIDAY. A WARMER 
DAY IS EXPECTED FRIDAY...BUT THEN IT WILL BE COLDER FRIDAY NIGHT 
WITH FROST POSSIBLE MAINLY IN LOW-LYING AREAS SATURDAY MORNING. LOW 
PRESSURE WILL STRENGTHEN INLAND OVER THE WEEKEND FOR COOLER WEATHER 
AND STRONGER ONSHORE FLOW. THE BUILDING MARINE LAYER WILL BRING MORE 
CLOUDS OVER THE WEEKEND...AND RAIN WILL BE POSSIBLE STARTING SUNDAY. 

&&

.DISCUSSION...FOR SOUTHWEST CALIFORNIA INCLUDING SAN DIEGO... 
ORANGE...SOUTHWEST SAN BERNARDINO AND WEST RIVERSIDE COUNTIES.

SKIES WERE MOSTLY CLEAR...WITH HAZY CONDITIONS CONTINUING NEAR THE 
COAST. OFFSHORE FLOW WAS STARTING TO DEVELOP AS WINDS WERE NORTHEAST 
AT CAMPO...GUSTING TO 24 MPH. THE SAN DIEGO TO TONOPAH PRESSURE 
GRADIENT WAS ALREADY 6.3 MB OFFSHORE. ACARS SOUNDINGS HAVE SHOWN 
SOME NE FLOW BELOW 4000 FT MSL...BRIEFLY TO AROUND 2000 FT OVER 
KSAN. STRATUS SHOULD MOSTLY BE ABSENT TONIGHT...BUT WITH THE 
RESIDUAL MARINE LAYER ALONG THE SAN DIEGO COUNTY COAST...PATCHY LOW 
CLOUDS AND FOG COULD OCCUR AT LEAST THIS EVENING.

FROM PREVIOUS DISCUSSION...

TONIGHT THE OFFSHORE SURFACE GRADIENTS STRENGTHEN AS HIGH PRESSURE 
BUILDS S THROUGH THE GREAT BASIN. WITH SOME UPPER SUPPORT...WIND 
GUSTS IN 30 TO 40 MPH RANGE ARE LIKELY BY MORNING IN THE WIND PRONE 
VALLEYS AND FOOTHILL AREAS. RH WILL DROP BELOW 15 PERCENT AS WELL ON 
FRI SO THE FIRE THREAT WILL BE ELEVATED...ESPECIALLY IN THE SANTA 
ANA MOUNTAINS AND FOOTHILLS WHERE RAINFALL HAS BEEN MEAGER. COLD AIR 
ADVECTION ON NORTHEAST WINDS FRIDAY WILL REALLY PUT A LID ON TEMPS 
IN THE MOUNTAINS AND DESERTS. EXPECT HIGHS ONLY IN THE 50S IN THE 
HIGH DESERTS...THE 60S IN THE LOW DESERTS...AND THE 40S AND LOW 50S 
IN THE MOUNTAINS. IN CONTRAST...DOWNSLOPE WARMING WILL PUSH 
TEMPERATURES INTO THE UPPER 60S AND 70S IN THE COASTAL ZONES. THIS 
WILL BE A FAIRLY SHORT WIND EVENT THAT WILL END FRIDAY EVENING.

FOR FRI NIGHT AND SAT MORNING...THE FOCUS SHIFTS TO COLD AND FROST. 
WITH LIGHT WINDS...CLEAR SKIES...AND VERY DRY AIR IN PLACE...MIN 
TEMPS WILL LIKELY FALL BELOW THE FREEZING POINT IN THE VALLEYS AND 
DESERTS...AND EVEN THE COLDER COASTAL AREAS. A FROST ADVISORY WILL 
LIKELY BE NEEDED FOR FRI NIGHT INTO SAT MORNING. 

LOOKING AHEAD...THE MASSIVE E PAC RIDGE BREAKS DOWN AS LOW PRESSURE 
FROM THE NORTH SAGS SOUTHWARD THROUGH THE LOWER 48. MODELS ARE NOT 
IN AGREEMENT ON JUST HOW FAR WEST THIS SYSTEM WILL DIG. EITHER WAY 
WE END UP WITH SOME LIGHT RAIN EARLY NEXT WEEK. A BETTER WESTERLY 
FLOW IS PROJECTED LATER NEXT WEEK FOR MORE PERIODS OF RAIN AS 
SYSTEMS MOVE WITH THE POLAR JET THROUGH CA. ALL THINGS CONSIDERED WE 
SHOULD BE WET OFF AND ON MUCH OF THE WEEK.

&&

.AVIATION...
031930Z...MARINE LAYER DEPTH LOWERED TO AROUND 2000 FEET THIS 
AFTERNOON AND SHOULD LOWER FURTHER TO AROUND 1500 FEET TONIGHT AND 
TO NEAR SEA LEVEL BY SUNRISE ON FRIDAY. DEVELOPING OFFSHORE FLOW HAS 
PUSHED THE STRATUS WELL OFF THE COAST. STRATUS COULD COME BACK 
ONSHORE THIS EVENING AFTER SUNSET BUT SHOULD GET PUSHED BACK 
OFFSHORE BEFORE SUNRISE ON FRIDAY. THERE COULD BE A BRIEF PERIOD OF 
LIFR CONDITIONS AT THE COASTAL AIRPORTS LATE TONIGHT BEFORE THE 
STRATUS CLEARS THE COAST.

ABOVE THE MARINE LAYER...A MOSTLY CLEAR SKY WITH UNRESTRICTED 
VISIBILITIES WILL CONTINUE THROUGH FRIDAY.

LOCAL GUSTY NORTHEAST WINDS WITH ASSOCIATED UP AND DOWN DRAFTS AND 
LOW LEVEL WIND SHEAR ARE EXPECTED TO DEVELOP LATE TONIGHT AND FRIDAY 
MORNING BELOW PASSES AND CANYONS.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...NONE. 

&&

$$

PUBLIC...JAD/MAXWELL
AVIATION...HORTON