AREA FORECAST DISCUSSION

 
 FXUS66 KSGX 281551
 AFDSGX
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SAN DIEGO CA
 850 AM PDT THU AUG 28 2008
 
 .SYNOPSIS...A DEEP MARINE LAYER WILL KEEP SKIES MOSTLY CLOUDY AT THE 
 BEACHES TODAY BUT THE MARINE LAYER WILL SHRINK ON FRIDAY AND MOSTLY 
 SUNNY DAYS AREA LIKELY FOR THE BEACHES THIS LABOR DAY WEEKEND.   
 INCREASING MONSOON MOISTURE WILL BRING A RETURN OF THUNDERSTORMS 
 FRIDAY AND SATURDAY. SOME OF THESE MAY MOVE WEST OF THE MOUNTAINS 
 AND ACROSS THE VALLEYS AND COAST FRIDAY NIGHT AND SATURDAY. DRIER 
 AND MORE STABLE AIR WILL MOVE ACROSS THE REGION SUNDAY AND LABOR 
 DAY. NEXT WEEK AN UPPER LEVEL TROUGH WILL BRING SLIGHT COOLING AND A 
 RETURN OF THE MARINE LAYER.  
 
 &&
 
 .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
 SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
 COUNTIES...
 
 .SHORT TERM...TODAY THROUGH SATURDAY...
 MONSOON MOISTURE PULSING TOWARDS SW CALIFORNIA BUT ALL FACTORS NOT 
 QUITE IN ALIGNMENT TODAY TO GENERATE THUNDERSTORMS OVER 
 MOUNTAINS/DESERTS. THE REMNANT CIRCULATION FROM THE MESO SCALE 
 CONVECTIVE COMPLEX THAT WAS OVER NW ARIZONA LAST NIGHT IS CURRENTLY 
 MOVING WEST SOUTHWESTWARD AROUND 12 KTS ACROSS IMPERIAL/EASTERN SAN 
 DIEGO COUNTY. THIS FEATURE SHOULD TURN MORE TOWARDS THE WEST LATER 
 THIS MORNING ACROSS SAN DIEGO COUNTY AND THEN NORTHWEST THIS 
 AFTERNOON AS IT MOVES OVER THE COASTAL WATERS AND CONTINUES ITS 
 PATH  AROUND THE PERIPHERY OF THE HIGH CELL TO THE NORTH. IN ITS 
 WAKE CONVERGENCE ALOFT WILL GENERATE DOWNWARD MOTION WHICH SHOULD BE 
 SUFFICIENT TO OFFSET THE LOW/MID LEVEL CONVERGENCE OVER THE 
 MOUNTAINS THIS AFTERNOON. ALSO TRIGGER TEMPS WILL BE QUITE HIGH...93 
 FOR 5000 FEET AND 103 FOR 3500 FEET...SO ONLY MODERATE CUMULUS AT 
 WORST EXPECTED OVER HIGHER MOUNTAINS TODAY. PLAN TO TAKE ADVANTAGE 
 OF THIS TEMPORARY BREAK IN ACTIVE CONVECTION TO INSTALL UPGRADES TO 
 WSR-88DS AT KSOX AND KNKX SO THEY WILL BE DOWN FOR A FEW HOURS THIS 
 MORNING. FOR TONIGHT THROUGH FRIDAY THE LOW/MID LEVEL MONSOON 
 MOISTURE INCREASES TO A DEPTH OF AT LEAST 10000 FEET DUE TO THE 
 INCREASING SOUTHEAST FLOW. WITH NO INHIBITORS IN PLACE...DIURNAL 
 HEATING FRIDAY SHOULD LEAD TO SCATTERED TO WIDESPREAD THUNDERSTORMS 
 FORMING OVER MOUNTAINS. FOR FRIDAY NIGHT THROUGH SATURDAY WITH 
 PREVAILING FLOW BECOMING MORE EAST DUE TO SHIFTING OF HIGH 
 CELL...THUNDERSTORMS SHOULD DRIFT WEST OF THE MOUNTAINS AND ANY 
 EMBEDDED SHORT WAVES/REMNANT UPSTREAM CIRCULATION CENTERS CAUGHT UP 
 IN THE FLOW COULD GENERATE SQUALL LINES THAT WOULD PROPAGATE 
 WESTWARD ACROSS THE VALLEYS/COAST/AND COASTAL WATERS...SOMEWHAT 
 ANALOGOUS TO THIS PAST MONDAY. MOVING ON TO THE MORE PRESSING 
 QUESTION...WHEN WILL THE STRATUS CLEAR. MARINE LAYER IS DEEPER AND 
 DEEPENING THIS MORNING FROM WEAK LIFTING AHEAD OF ABOVE MENTIONED 
 CIRCULATION CENTER. RULE OF THUMB USING A 1000 FOOT CLOUD LAYER 
 WOULD SAY STRATUS NOT BREAKING UP UNTIL 1020 PDT. A NAM12 MODEL 
 CROSS SECTION ALONG THE COASTS SHOWS THE MEAN LAYER RELATIVE 
 HUMIDITY IN THE LOWER 2000 FEET STAYING ABOVE 90 PERCENT ALONG SAN 
 DIEGO COAST ALL DAY...WITH ORANGE COUNTY COAST DROPPING DOWN TO 
 AROUND 75 PERCENT FOR ONLY A BRIEF 3 HOUR PERIOD...BETWEEN 1400-1800 
 PDT...AND THEN HUMIDITY ROCKETS BACK UP TO +90 PERCENT...CLOSER TO 
 100 PERCENT IN LOWER 1000 FEET AFTER 2000 PDT. SO LOOKS LIKE 
 LIMITED/LATE PATCHY CLEARING FOR SAN DIEGO COAST TODAY AND EARLY TO 
 MID AFTERNOON CLEARING FOR ORANGE COUNTY COAST...WITH HAZY SUNSHINE 
 THIS AFTERNOON FOR THE VALLEYS. MUCH BETTER PROSPECTS FOR SUNSHINE 
 ALONG THE COAST ON FRIDAY AS INCREASING INSTABILITY MENTIONED ABOVE 
 WILL BE SPREADING WESTWARD ACROSS THE ENTIRE 
 AREA...ERODING/ELIMINATING THE CAPPING INVERSION AND MIXING OUT THE 
 MARINE LAYER SO STRATUS SHOULD BREAK UP MUCH EARLIER ON 
 FRIDAY...AROUND 0900 PDT...AND GONE BY 1000 PDT WITH NO RETURN 
 FRIDAY NIGHT/SATURDAY...OR AT WORST PATCHY/SCATTERED STRATUS 
 CONFINED TO BELOW 300 FEET OVER WATER AND SOUTH SAN DIEGO COUNTY 
 COAST/NORTHERN BAJA CALIFORNIA.  
 
 .LONG TERM...SATURDAY NIGHT THROUGH WEDNESDAY...
 ALL MODELS IN AGREEMENT WITH RELATIVELY STRONG TROUGH MOVING INLAND 
 TO THE NORTH SATURDAY NIGHT...RESULTING IN INCREASING WEST TO 
 SOUTHWEST WINDS AND DRIER/STABLE AIR MASS MOVING OVER SOUTHWEST 
 CALIFORNIA SUNDAY THROUGH AT LEAST MONDAY AND POSSIBLY LINGERING 
 THROUGH REMAINDER OF NEXT WEEK. MARINE LAYER SHOULD BEGIN TO REBUILD 
 BY SUNDAY NIGHT AIDED BY A COASTAL EDDY CIRCULATION...HOWEVER LABOR 
 DAY LIKELY TO BE MOSTLY SUNNY AT THE BEACHES WITH ANY STRATUS/FOG 
 CLEARING WELL BEFORE 1000 PDT. AFTER MONDAY A WEEK UPPER LOW SLOWLY 
 APPROACHES FROM THE WEST SOUTHWEST...AND THE RESULTING WEAK CYCLONIC 
 FLOW ALOFT SHOULD AID IN MAINTAINING A COASTAL EDDY AND DEEPENING 
 THE MARINE LAYER. FAIR WEATHER EXPECTED ELSEWHERE. 
 
 &&
 
 .AVIATION...
 271520Z...MARINE LAYER STRATUS THICKNESS THIS MORNING ABOUT 1K FT 
 WITH BASES NEAR 1K FT MSL AND TOPS TO FL020. THIS SOLID MARINE DECK 
 SHOULD DELAY CLEARING AT THE COASTAL AIRPORTS UNTIL AROUND 19Z 
 TIME FRAME. FARTHER INLAND...EXPECT THE CIGS TO LIFT BETWEEN 16Z AND 
 17Z...ALTHOUGH 3-5SM VIS RESTRICTIONS WILL CONTINUE IN HAZE UNTIL  
 AROUND 20Z. AT THE BEACHES...AREAS OF CIGS/HAZE ARE LIKELY TO LINGER 
 THROUGH THE AFTERNOON. ABOVE THE MARINE LAYER VIS WILL BE 
 UNRESTRICTED WITH SOME SCT TO LOCALLY BKN CLOUDS AT FL150.
 
 
 
 &&
 
 .SGX WATCHES/WARNINGS/ADVISORIES...
 CA...NONE.
 PZ...NONE.
 
 &&
 
 

 
 PUBLIC/FIRE WEATHER...BALFOUR
 AVIATION/MARINE...JAD
 
 NWS ON THE WEB AT WEATHER.GOV/SANDIEGO
 
 
 
 
 
 

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