Forecast Discussions mentioning ACARS, received at FSL on 09/03/99

MAIN DILEMMA FACING US THIS AFTERNOON IS WILL MARINE LYR REFORM SOLIDLY TONIGHT SOUTH OF POINT CONCEPTION OR WILL IT REMAIN CLEAR TO PARTLY CLOUDY. AT THIS POINT...ALL INDICATIONS ARE THAT IT WILL REFORM RATHER SOLIDLY. 4 FACTORS ARE LEADING ME TO THAT CONCLUSION. FIRST...ACARS SOUNDINGS CONTINUE TO INDICATE MARINE LYR DEPTH IS AROUND 4000 FEET. THE LACK OF ANY SIGNIFICANT LOWERING TREND WOULD LEAD ME TO GO WITH A PERSISTENCE FORECAST TNT. SECOND...ONSHORE GRADIENTS CONTINUE TO TREND SLIGHTLY ONSHORE...INDICATING GREAT BASIN SURFACE PRESSURES ARE STILL FALLING. THIRD...AN EDDY CIRCULATION IS STILL EVIDENT IN THE VISIBLE SATELLITE IMAGERY WITH PLENTY OF MARINE LYR CLOUDS OFFSHORE. AND LASTLY...WATER VAPOR IMAGERY INDICATES ANOTHER WEAK SHORT WAVE WILL DROP DOWN THRU THE TROF TNT AND MAINTAIN CYCLONIC FLOW ALOFT OVER SO CAL. WITH ALL THESE FACTORS POINTING TOWARDS A RETURN TO MOSTLY CLOUDY CONDITIONS TNT...WILL GO WITH A PERSISTENCE FORECAST TNT WHICH IS BASICALLY LITTLE CHANGE FROM THE PREVIOUS FORECAST. ETA/NGM/AVN ALL AGREE THAT TROF WILL SLOWLY LIFT OUT DURING THE DAY FRIDAY WITH HEIGHTS SLOWLY RECOVERING TO NEAR NORMAL BY SUN. THUS...LOOK FOR SLIGHTLY WARMER TEMPS EACH OF THE NEXT FEW DAYS...MAINLY INLAND AREAS WHERE MARINE INFLUENCE WILL BE MUCH WEAKER. SUPPORT FOR EDDY CIRCULATION IS ESSENTIALLY GONE SO EXPECT EDDY TO DISSIPATE WITHIN THE NEXT 24 HOURS OR SO. THIS WILL ALLOW SKIES TO CLEAR EARLIER AND TEMPS TO WARM WEST OF THE MOUNTAINS. MTNS AND DSRTS WILL BENEFIT FROM A SLIGHLY WARMER AIRMASS WHICH WILL BRING TEMPS THERE UP A FEW DEGREES BY THE WEEKEND.

NO SIGNIFICANT CHANGES EXPECTED ALONG THE CENTRAL COAST NEXT FEW DAYS. WITH NW FLOW A LITTLE WEAKER TODAY...TEMPS WERE GENERALLY A FEW DEGREES WARMER NEAR THE COAST WHILE INLAND AREAS WERE VERY CLOSE TO WEDNESDAY'S LEVELS. EXPECT NW FLOW TO INCREASE SLIGHTLY NEXT TWO DAYS SO COASTAL AREAS MAY BE A DEGREE OR TWO COOLER THAN TODAY WHILE INLAND AREA TEMPS GO UP DUE TO AN INCREASE IN THICKNESSES.

ALTHOUGH 12Z AVN MAINTAINS A WEAK UPR LEVEL TROF IN THE VICINITY OF THE W CST THROUGH SUN...I EXPECT TEMPS WILL CLIMB BACK TO NEAR NORMAL LEVELS BY MON. HOWEVER...NO SIGNIFICANT INCREASE IN TEMPS OR A RETURN TO MONSOONAL TSTORMS IS EXPECTED FOR THE NEXT SEVERAL DAYS.

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TYPICAL CATALINA EDDY CLOUD PATTERN INDICATED ON THE VISIBLE SATELLITE IMAGERY THIS MORNING. PLENTY OF CLEARING OFFSHORE BUT THICK CLOUDS OVER LAND. AS IS COMMON WITH THIS TYPE OF PATTERN...MANY BEACH AREAS WILL LIKELY SEE BETTER CLEARING TODAY THAN VALLEYS...AND CURRENT ZONES HANDLE THIS WELL. ACARS SOUNDINGS INDICATE MARINE LYR DEPTH HAS RISEN FROM ABOUT 3000 FEET OVERNIGHT TO ABOUT 4000 AS OF 15Z. THIS DEEPENING TREND COUPLED WITH AN INCREASING ONSHORE FLOW WILL MAKE FOR A MUCH COOLER THAN NORMAL DAY IN THE VALLEYS WHERE AFTN TEMPS WILL GENERALLY REMAIN IN THE 70S. 12Z ETA/NGM DO A DECENT JOB INITIALIZING THE UPR TROF OVER THE WEST COAST...THO NGM IS A LITTLE SLOWER IN MOVING IT EASTWARD. HOWEVER...BOTH MODELS MAINTAIN LOWER THAN NORMAL HEIGHTS OVER THE AREA FOR THE NEXT 48 HOURS. THUS...A WARMING TREND IS EXPECTED BUT IT WILL BE A SLOW UPWARD TREND AT BEST. EDDY CIRCULATION WILL LIKELY WEAKEN TONIGHT AS SUPPORT FOR THE ROTATION HAS ESSENTIALLY DIED OUT. BY SUN AND MON...TEMPS IN THE VALLEYS SHOULD BE APPROACHING NORMAL LEVELS. NO UPDATES PLANNED ATTM.

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UPPER LOW CENTERED OVER SOUTHWEST IDAHO THIS MORNING...IS FORECASTED TO MOVE GRADUALLY EASTWARD TODAY. WHILE HEIGHTS WILL RISE OVER CALIFORNIA...WEAK TROUGHING WILL HANG BACK OVER THE CENTRAL AND NORTHERN PORTIONS OF THE STATE THROUGH SATURDAY...WITH CONTINUED MODERATE ONSHORE FLOW AT THE SURFACE.

12Z SOUNDING AT VANDENBERG THIS MORNING SHOWED SIGNIFICANT DECREASE IN MARINE LAYER DEPTH...DOWN TO AROUND 1700 FEET...WHICH RESULTED IN SOME EARLY MORNING DENSE FOG ACROSS THE CENTRAL COAST. HOWEVER...ACARS SOUNDINGS ACROSS THE LA BASIN STILL INDICATED MARINE LAYER DEPTHS OVER 4000 FEET...WITH SOME STRATUS LINGERING ACROSS THE LOWER COASTAL SLOPES. STRATUS PATTERN REAMINS RATHER CHAOTIC...DUE TO PASSAGE OF UPPER TROUGH WEAKENING MARINE INVERSION. SOME STRATOCUMULUS CLOUDS ARE EXPECTED TO LINGER ACROSS PORTIONS OF LA/VTU/SBA COUNTIES THROUGH EARLY AFTERNOON...DUE TO FAIRLY MOIST LOW LEVELS. AS HEIGHTS/ THICKNESSES GRADUALLY INCREASE THROUGH SATURDAY...AND MARINE LAYER SHRINKS...LOOK FOR MODEST WARMING TREND IN ALL AREAS...ESPECIALLY INLAND AREAS.

LONGER PERIOD SWELL...MOSTLY AROUND 20 SECONDS...SHOWING UP ON BUOYS AND SWELL MODEL THIS MORNING. THIS SWELL ORIGINATED FROM A STORM JUST EAST OF NEW ZEALAND 8 TO 9 DAYS AGO...SO THERE WILL BE A SSW ORIENTATION TO THE SWELL. EXPECT THIS SWELL TO GRADUALLY BUILD TODAY ACROSS SOUTH FACING BEACHES...WITH MAX SETS UP TO 6 FEET ACROSS LA/VTU COUNTY BEACHES...AND PERHAPS EVEN HIGHER FURTHER SOUTH.

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