291 FXUS66 KLOX 201610 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 910 AM PDT SAT OCT 20 2012 .SYNOPSIS... A DEEPENING MARINE LAYER WILL BRING LOW CLOUDS...FOG...AND DRIZZLE OR LIGHT RAIN AND COOLER TEMPERATURES THROUGH MONDAY. A LOW PRESSURE SYSTEM WILL BRING A CHANCE OF RAIN TO THE AREA MONDAY AND TUESDAY. HIGH PRESSURE IS EXPECTED TO BRING DRY AND WARMER CONDITIONS BY THE END OF THE WEEK. && .SHORT TERM (TODAY-MON)... THE UPPER LEVEL LOW THAT IS THE REMNANTS OF HURRICANE PAUL HAS FINALLY OPENED UP INTO A TROUGH AND WILL SWING THROUGH SOUTHERN CALIFORNIA TODAY AND TONIGHT. THIS HAS ALLOWED THE MARINE LAYER TO DEEPEN QUICKLY TO AROUND 3500 FEET THIS MORNING...WHICH HAS RESULTED IN STRATUS PUSHING DEEP INTO THE VALLEYS AND COASTAL SLOPES. THIS HAS ALSO BROUGHT FAIRLY WIDESPREAD DRIZZLE TO THE AREA...THAT IS RESULTING IN A FEW AREAS PICKING UP MEASURABLE ACCUMULATIONS. WITH ONSHORE GRADIENTS EXPECTED TO RUN AROUND 4 MB STRONGER ONSHORE THAN 24 HOURS AGO...THERE IS A GOOD CHANCE THAT CLEARING WILL BE SLOW AND PATCHY AT BEST THIS AFTERNOON. THE INVERSION IS FAIRLY WEAK HOWEVER...SO THIS SCENARIO IS FAR FROM LOCKED IN...BUT A MOSTLY GLOOMY AND COOL AFTERNOON IS THE MOST LIKELY OUTCOME. GUSTY ONSHORE WINDS ARE ALSO EXPECTED OVER THE INTERIOR AREAS WITH THE STRONG ONSHORE TRENDS...ESPECIALLY IN THE ANTELOPE VALLEY. MADE A MINOR UPDATE TO THE FORECAST TO ADD 20 POPS TO MOST COASTAL AND VALLEY AREAS THIS MORNING...AND UPPED CLOUDS A BIT IN THE AFTERNOON WITH A LITTLE MORE COOLING TO TEMPERATURES AS A RESULT. ***FROM PREVIOUS DISCUSSION*** BY TONIGHT...THE CUTOFF LOW THAT HAS BEEN SPINNING OFF THE COAST OF BAJA THE PAST SEVERAL DAYS WILL FINALLY GET EATEN UP BY THE BROAD UPPER LEVEL TROUGH DEEPENING OVER SOUTHERN CALIFORNIA. AS H5 HEIGHTS AND THICKNESS LVLS LOWER WITH THIS DEEPENING TROUGH...THE MARINE LAYER WILL DEEPEN EVEN FURTHER...TO AROUND 4500 FT BY TONIGHT INTO SUNDAY MORNING. LATEST NAM12 CROSS SECTION SHOWS SOME ADDITIONAL LIFT WITH THIS DEEP MARINE LAYER. AT THE LEAST THERE WILL BE AREAS OF DRIZZLE ACROSS LOS ANGELES AND VENTURA COUNTIES TO THE COASTAL SLOPES. 20 PERCENT POPS LOOKS GOOD AS THERE SHOULD BE SOME MEASURABLE RAIN INTO SUNDAY MORNING...ESPECIALLY AROUND THE FOOTHILLS WHERE THE ADDITIONAL TOPOGRAPHY LIFT SHOULD ACT LIKE A SPONGE AND ENHANCE RAINFALL AMOUNTS TO OVER A TENTH OF AN INCH...ESPECIALLY ALONG THE SAN GABRIEL MOUNTAIN FOOTHILLS LIKE A CANADA/FLINTRIDGE AND LA CRESCENTA AREAS. SKIES ONCE AGAIN WILL HAVE A TOUGH TIME CLEARING OUT ACROSS THE COASTAL PLAIN WITH ONLY PARTIAL CLEARING EXPECTED FOR THE VALLEYS SOUTH OF POINT CONCEPTION. A COOLING TREND WILL CONTINUE INTO SUNDAY WITH MOST AREAS AWAY FROM THE MOUNTAINS ONLY REACHING THE UPPER 60S TO LOWER 70S. TEMPS WILL BE COOLER THAN NORMAL FOR THIS TIME OF YEAR. BY MONDAY...A COLD 532 DM UPPER LOW SITUATED OFF THE COAST OF WASHINGTON WITH A VERY DEEP TROUGH EXTENDING ACROSS ALL OF CALIFORNIA WILL SWING A FEW EMBEDDED SHORTWAVES ACROSS THE NORTHERN PORTION OF THE FORECAST AREA ON MONDAY. THE NAM-WRF...GFS AND ECMWF ARE IN GOOD AGREEMENT BRINGING IN A COLD FRONT INTO THE SLO AND SBA COUNTIES ON MONDAY...THEN AS THE FRONT HOLDS TOGETHER MOVE INTO VENTURA AND LOS ANGELES COUNTIES LATE MONDAY NIGHT INTO TUESDAY. AT THIS TIME...BEST GUEST FOR PRECIP ESTIMATES WILL BE BETWEEN A TENTH TO A THIRD OF AN INCH FOR AREAS N OF POINT CONCEPTION. WHILE RAINFALL TOTALS SOUTH OF POINT CONCEPTION WILL BE LESS AS THE FRONT WEAKENS OVER VENTURA AND LA COUNTIES. SNOW LEVELS WILL ALSO REMAIN ABOVE RESORT LEVELS TO AROUND 7500 FT MONDAY...THEN LOWERING TO AROUND 6500 FT BY TUESDAY. THERE COULD BE A QUICK DUSTING OF SNOW AT HIGH RESORT LEVELS BY TUESDAY. BUT WITH LIMITED MOISTURE TO WORK WITH...DONT GET TOO EXCITED. .LONG TERM (TUE-FRI)...BOTH GFS AND ECMWF ARE IN FAIRLY GOOD AGREEMENT THROUGH THE EXTENDED PERIOD...EXCEPT THE GFS ADVERTISES A RIDGE BUILDING OFF THE CALIFORNIA COAST WELL INTO THE GULF OF ALASKA WHILE THE ECMWF CONTINUES A ZONAL TO WEAK TROUGH OVER THE WEST. EARLIER MODEL RUNS WERE SLOWER WITH THE ARRIVAL AND EXIT OF THE RAINY PERIOD THROUGH THE FORECAST AREA. BOTH MODELS HAVE BACKED OFF SOME WITH THE PROGRESSION OF A SECONDARY SHOT OF MOISTURE TUESDAY NIGHT INTO WED. HOWEVER...THE UPPER TROUGH WILL CONTINUE TO REMAIN OVERHEAD KEEPING TEMPS QUITE COOL AND CONTINUED LOW LEVEL MOISTURE TO BRING A FEW PERIODS OF SHOWERS AFTER THE MAIN RAIN THREAT ON MONDAY TO EARLY TUESDAY MORNING. BY WEDNESDAY AFTERNOON...EXPECT CLEAR TO PARTLY CLOUDY SKIES ACROSS MUCH OF THE FORECAST AREA. WEDNESDAY WILL BEGIN A MILD WARMING TREND INTO THURSDAY BEFORE OFFSHORE FLOW DEVELOPS WARMING UP COAST AND COASTAL VALLEYS LATE NEXT WEEK. WARMEST TEMPS SHOULD REACH THE MID 80S BY FRI...WITH ADDITIONAL WARMING BY NEXT WEEKEND. && .AVIATION...20/1130Z... DEEP MARINE LAYER AND GOOD ONSHORE FLOW HAS ENTRENCHED STRATUS ACROSS ALL COASTAL/VALLEY TAF SITES...WITH GENERALLY MVFR CONDS SOUTH OF POINT CONCEPTION...AND LIFR/IFR CONDS NORTH OF POINT CONCEPTION. CLEARING THIS AFTERNOON WILL BE SLOW AND SHORT-LIVED AS STRATUS WILL FILL IN QUICKLY THIS EVENING. KLAX...MODERATE CONFIDENCE IN 12Z TAF. THERE IS A 40% CHANCE THAT CIGS WILL REMAIN THROUGH THE AFTERNOON. KBUR...MODERATE CONFIDENCE IN 12Z TAF. THERE IS A 40% CHANCE THAT CIGS WILL REMAIN THROUGH THE AFTERNOON. && .LOX WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY (SEE LAXMWWLOX). && $$ PUBLIC...KITTELL/KAPLAN AVIATION...RAT SYNOPSIS...CK WWW.WEATHER.GOV/LOSANGELES