AREA FORECAST DISCUSSION

 
 FXUS66 KSGX 251704
 AFDSGX
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SAN DIEGO CA
 905 AM PST WED NOV 25 2009
 
 .SYNOPSIS...HIGH PRESSURE ALOFT AND OFFSHORE FLOW WILL BRING 
 CLEAR...WARM WEATHER TODAY AND THURSDAY. GUSTY NORTHEAST WILL 
 CONTINUE THROUGH AND BELOW THE MOUNTAIN CANYONS AND PASSES. A 
 STRONG...FAST MOVING TROUGH OF LOW PRESSURE WILL BRING COOLER 
 WEATHER FRIDAY AND A SLIGHT CHANCE OF LIGHT RAIN SATURDAY. A 
 POTENTIALLY STRONG OFFSHORE WIND EVENT IS POSSIBLE SUNDAY AND 
 MONDAY. 
 
 &&
 
 .DISCUSSION...FOR SOUTHWEST CALIFORNIA INCLUDING SAN DIEGO... 
 ORANGE...SOUTHWEST SAN BERNARDINO AND WEST RIVERSIDE COUNTIES.
 
 OFFSHORE WINDS GUSTING TO 20 TO 30 MPH WERE BLOWING THROUGH THE 
 MOUNTAIN PASSES THIS MORNING. THE STRONGEST WIND GUSTS OF 40-50 MPH 
 WERE LIMITED TO FREMONT CANYON IN THE THE SANTA ANA MOUNTAINS...NEAR 
 THE ANAHEIM HILLS FIRE. 
 
 THE WINDS KEPT MORNING LOW TEMPERATURES FROM FALLING TOO FAR AND 
 WERE IN THE 50S AND 60S. IN CONTRAST...WIND SHELTERED AREAS GOT 
 QUITE COLD (14 DEGREES AT BALDWIN LAKE).     
 
 THIS OFFSHORE WEATHER PATTERN DOES NOT CHANGE THROUGH THURSDAY WITH 
 UPPER LEVEL RIDGING AND SURFACE HIGH PRESSURE OVER THE GREAT BASIN. 
 DOUBLE DIGIT OFFSHORE SURFACE PRESSURE GRADIENTS WILL CONTINUE TO 
 BRING BLUSTERY NORTHEAST WINDS THROUGH THE PASSES. THE STRONGEST 
 WIND ARE LIKELY TO OCCUR LATE TONIGHT THROUGH THURSDAY MORNING.
 
 THANKSGIVING DAY WILL BE A CARBON COPY OF TODAY WITH CLEAR SKIES AND 
 DAYTIME HIGHS 6 TO 12 DEGREES ABOVE AVERAGE. DURING THE AFTERNOON 
 SURFACE RIDGE BEGINS TO SHIFT EAST AND THE OFFSHORE WINDS WILL TAPER 
 OFF AS THE GRADIENTS WEAKEN. ONSHORE FLOW WILL INCREASE FRIDAY AHEAD 
 OF AN APPROACHING TROUGH THAT WILL BRING COOLER WEATHER AND A RETURN 
 OF SOME MARINE LAYER CLOUDS. THE MARINE LAYER WILL INITIALLY BE 
 QUITE SHALLOW AND PATCHY DENSE FOG IS POSSIBLE AT THE COAST DURING 
 THE DAY. THE 12Z NAM MODEL FORECASTS EXPLOSIVE GROWTH OF THE MARINE 
 LAYER FRIDAY NIGHT AND SATURDAY...DEEPENING TO OVER 5000 FEET 
 SATURDAY AFTERNOON. BOTH THE NAM AND GFS GENERATE AROUND A TENTH OF 
 AN INCH OF PRECIP. 
 
 IT HAS BEEN 161 DAYS SINCE MEASURABLE RAIN AT LINDBERGH FIELD. THE 
 LAST TIME IT RAINED WAS JUNE 16TH WHEN .03 INCHES FELL. THE LONG DRY 
 SPELL MAY END THIS WEEKEND. IF IT DOES NOT END AND MEASURABLE RAIN 
 DOES NOT FALL AT LINDBERGH FIELD...IT WILL MARK THE FIRST TIME A 
 STREAK OF DRY WEATHER THIS LONG HAS EXTENDED INTO THE MONTH OF 
 DECEMBER. 
 
 &&
 
 .LONG TERM (SUNDAY-TUESDAY)...STRONG OFFSHORE FLOW FILLS IN BEHIND 
 THE UPPER LOW ON SUNDAY AND MONDAY. THE LATEST ECMWF...GFS AND DGEX 
 INDICATE NE WINDS OF 30-40 KT AT 850 MB WITH MODEST OFFSHORE 
 PRESSURE GRADIENTS. IT WILL STILL BE COOL THOUGH DUE TO COLD 
 ADVECTION FROM THE NORTH. MOSTLY CLEAR AND WARMER MONDAY AND 
 TUESDAY. 
 
 &&
 
 .AVIATION...
 251430Z...OFFSHORE FLOW WILL KEEP THE MARINE LAYER NEAR SEA LEVEL 
 THROUGH THANKSGIVING DAY. SOME RECOVERY IS EXPECTED ON FRIDAY. AS A 
 RESULT...A MOSTLY CLEAR SKY WITH UNRESTRICTED VISIBILITIES WILL 
 CONTINUE THROUGH THANKSGIVING. SOME VISIBILITY RESTRICTIONS CAN BE 
 EXPECTED IN THE VICINITY OF A WILDFIRE LOCATED IN THE SANTA ANA 
 RIVER CANYON BETWEEN KAJO AND KFUL.
 
 LOCAL GUSTY NORTHEAST WINDS WITH ASSOCIATED UP AND DOWN DRAFTS AND 
 LOW LEVEL WIND SHEAR CAN BE EXPECTED BELOW PASSES AND CANYONS 
 THROUGH THANKSGIVING DAY.  HORTON
 
 &&
 
 .MARINE...
 MODERATE TO LARGE WNW SWELL TO ARRIVE THURSDAY NIGHT AND CONTINUE 
 THROUGH SATURDAY. WAMIII MODEL FOR SEVERAL DAYS HAS BEEN ADVERTISING 
 A RAPID INCREASE IN SWELL HEIGHTS LATE THURSDAY AFTERNOON/EVENING 
 REACHING 8 FT AT 16 SECONDS FROM 295 DEGREES OVERNIGHT/EARLY FRIDAY 
 MORNING. THE CURRENT OFFSHORE WIND FLOW PATTERN ENDS SHORTLY BEFORE 
 THIS AND CLIMATOLOGY FAVORS DENSE FOG NEAR SHORE AS FLOW RETURNS TO 
 ONSHORE. CONDITIONS COULD BE QUITE HAZARDOUS LATE THURSDAY THROUGH 
 FRIDAY MORNING ENTERING AND EXITING HARBORS AND BAYS. CONFIDENCE 
 FAIRLY HIGH IN HIGH SURF EVENT FRIDAY AND SATURDAY.
 
 &&
 
 .FIRE WEATHER...
 AIRMASS VERY DRY THIS MORNING WITH HUMIDITIES ALREADY IN THE TEENS 
 AND 20S IN THE VALLEYS AND FOOTHILLS. PREVAILING SANTA ANA 
 CONDITIONS AND EFFICIENT DRYING OF FUELS THROUGH THURSDAY AFTERNOON. 
 HUMIDITY RECOVER WILL START THURSDAY NIGHT AND FRIDAY WHEN A SHALLOW 
 MARINE LAYER MOVES INLAND...DEEPENING TO ABOUT 5000 FEET THROUGH 
 SATURDAY WHEN LIGHT RAIN OR DRIZZLE IS POSSIBLE. THEN WE BRACE FOR 
 ANOTHER POTENTIALLY STRONGER OFFSHORE WIND EVENT SUNDAY AND MONDAY. 
 
 .SGX WATCHES/WARNINGS/ADVISORIES...
 
 RED FLAG WARNING UNTIL 10 AM PST THURSDAY FOR THE SANTA ANA 
 MOUNTAINS AND FOOTHILLS. SEE LAXRFWSGX. 
 
 &&
 
 

 
 PUBLIC...MOEDE
 AVIATION...HORTON
 MARINE...BALFOUR
 FIRE WEATHER...MOEDE
 
 
 
 
 

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