571 FXUS66 KSGX 232126 AFDSGX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 200 PM PST MON NOV 23 2009 .SYNOPSIS...HIGH PRESSURE ALOFT AND WEAK OFFSHORE FLOW WILL BRING FAIR WEATHER WITH A WARMING TREND THROUGH THANKSGIVING DAY. COOLER WITH INCREASING CLOUDS TOWARD NEXT WEEKEND AS A LOW PRESSURE TROUGH APPROACHES FROM THE NORTHWEST. && .DISCUSSION...FOR SOUTHWEST CALIFORNIA INCLUDING SAN DIEGO... ORANGE...SOUTHWEST SAN BERNARDINO AND WEST RIVERSIDE COUNTIES. TODAY THROUGH THANKSGIVING DAY...CLEAR SKIES THIS AFTERNOON INTO TONIGHT WITH SFC PRESSURE GRADIENTS OFFSHORE TO THE NORTH AND EAST WITH ABOUT 9 MB SAN-TPH AND 1 MB SAN-IPL. AN UPPER LEVEL HIGH PRESSURE RIDGE AND A SFC HIGH OVER THE GREAT BASIN WILL BRING FAIR SKIES...OFFSHORE FLOW...MUCH WARMER WEATHER AND LOCAL GUSTY WINDS BELOW THE PASSES AND CANYONS THROUGH THANKSGIVING DAY. INCREMENTAL INCREASES IN 500 MB HEIGHTS AND 850 MB TEMPS WILL RESULT IN A FEW DEGREES OF WARMING EACH DAY...WITH DAYTIME HIGHS REACHING ABOUT 10 DEGREES ABOVE SEASONAL AVERAGES BY THANKSGIVING DAY. SKIES WILL BE MOSTLY CLEAR AS DRY OFFSHORE FLOW SCOURS OUT THE MARINE LAYER. THE OFFSHORE FLOW WILL BE DRIVEN PRIMARILY BY SFC PRESSURE GRADIENTS...WITH LITTLE UPPER LEVEL SUPPORT AND ONLY WEAK TO MODERATE SFC PRESSURE GRADIENTS. WIND GUSTS BELOW THE PASSES AND CANYONS WILL GENERALLY REMAIN BELOW 30 MPH...HOWEVER ISOLATED/OCCASIONAL GUSTS FROM 40-50 MPH ARE POSSIBLE IN THE MOST WIND-PRONE LOCATIONS. THE STRONGEST WINDS ARE EXPECTED TUESDAY MORNING WHEN THE PRESSURE GRADIENTS ARE STRONGEST. VERY DRY AIR IS EXPECTED WITH THE OFFSHORE FLOW THIS WEEK. INLAND HUMIDITIES WILL FALL BELOW 10 PERCENT EACH DAY BEGINNING TUESDAY AND CONTINUING THROUGH THURSDAY. THE COMBINATION OF LOCALLY BREEZY CONDITIONS AND VERY LOW HUMIDITIES WILL ELEVATE THE FIRE WEATHER HAZARD. FRIDAY THROUGH MONDAY...THE GFS AND ECMWF PROGS FOR LATER THIS WEEK ARE COMING INTO BETTER AGREEMENT AND SHOW THE RIDGE BREAKING DOWN FRIDAY AHEAD OF A DEEPENING LOW PRESSURE TROUGH THAT WILL BRING INCREASING CLOUDS AND SUBSTANTIAL COOLING THROUGH SATURDAY. AS THIS TROUGH MOVES TO THE EAST ON SUNDAY AND MONDAY...A COLDER AND POTENTIALLY WINDY OFFSHORE PATTERN COULD DEVELOP. && .AVIATION... 232000Z...CLEAR THROUGH TUESDAY WITH THIN HIGH CLOUDS AT TIMES. OFFSHORE FLOW WILL INCREASE TONIGHT WITH NORTHEAST WINDS 15-25 KT OVER THE MOUNTAINS AND INLAND VALLEYS THROUGH PASSES AND CANYONS WITH MODERATE TURBULENCE THROUGH TUESDAY MORNING AND AGAIN TUESDAY NIGHT THROUGH WEDNESDAY MORNING. && .SGX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ PUBLIC...PG AVIATION...WHITLOW