856 FXUS66 KLOX 170432 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 832 PM PST WED NOV 16 2011 .SYNOPSIS... WEAK OFFSHORE FLOW WILL KEEP THURSDAY DRY AND WARM. A STORM WILL MOVE SOUTH INTO THE AREA ON FRIDAY. THE STORM SYSTEM WILL MAINLY BRING CLOUDS AND COOLER WEATHER THROUGH THE WEEKEND...EXCEPT FOR A SLIGHT CHANCE OF RAIN AND MOUNTAIN SNOW BETWEEN FRIDAY AND SATURDAY. ANOTHER STORM SYSTEM WILL BRING A BETTER CHANCE OF RAIN TO THE AREA ON SUNDAY. && .UPDATE... A HIGH PRESSURE RIDGE OVER THE REGION IS FLATTENING THIS EVENING...EVIDENT BY THE LATEST WATER VAPOR IMAGERY. AN UPSTREAM COLD FRONT MOVING INTO THE PACIFIC NORTHWEST THIS EVENING WILL MOVE SOUTH OVER THE AREA BETWEEN EARLY FRIDAY MORNING AND FRIDAY NIGHT. THE MAIN INFLUENCE OF THE FRONT WILL BE TO BRING A COOL AND MORE CLOUDY PATTERN TO THE AREA. THE BEST CHANCE OF ANY PRECIPITATION WILL OCCUR FOR AREAS NORTH OF POINT CONCEPTION AND ALONG THE NORTHERN SLOPES OF THE MOUNTAINS. WITH NAM-WRF 850 MB MIXING RATIOS NEAR BETWEEN 4 AND 6 G/KG AS THE FRONT MOVES SOUTH INTO SAN LUIS OBISPO COUNTY...ENOUGH MOISTURE IS PRESENT TO POSSIBLY PRODUCE SOME SHOWERS. NAM BUFR TIME HEIGHT SECTIONS DO LOOK RATHER WEAK FOR MOISTURE...BUT STILL ENOUGH MOISTURE IS PRESENT WITH THE DEPTH OF MOISTURE AT KSBP UP TO 6000 FEET DEEP. FOR NOW...SLIGHT CHANCE POPS LOOK AGREEABLE AND NO CHANGES ARE PLANNED. AHEAD OF THE STORM SYSTEM ON THURSDAY...HIGH LEVEL MOISTURE WILL INCREASE. GFS 300MB AND 400 MB RELATIVE HUMIDITY VALUES INDICATE PERIODS OF BROKEN HIGH LEVEL CLOUDINESS STREAMING OVER THE AREA. NEAR THE COAST...THE MARINE LAYER WILL LIKELY PERSIST ESPECIALLY SOUTH OF POINT CONCEPTION. OFFSHORE GRADIENTS IN PLACE HAVE THINNED THE MARINE LAYER TO BETWEEN 700 TO 1000 FEET THIS EVENING. SOME CONCERN EXISTS FOR SOME PATCHY CLOUDS DEVELOPING FOR THE SANTA BARBARA COASTAL AREAS AND THIS WILL BE ADDED TO THE PACKAGE THROUGH THURSDAY MORNING. WITH THE DEPTH OF THE MARINE LAYER BEING THIN...PATCHES OF DENSE FOG ARE POSSIBLE EARLY THURSDAY MORNING. && .PREV DISCUSSION... SHORT TERM...THIS FIRST STORM SYSTEM IS EXPECTED TO TAKE TOO MUCH OF AN INLAND TRACK TO GENERATE MUCH IN THE WAY OF PRECIP, HOWEVER AREAS NORTH OF PT CONCEPTION COULD SEE A SHOWER OR TWO FRIDAY AND FRIDAY NIGHT. FURTHER SOUTH, STRONG ONSHORE FLOW PUSHING THE LOW LVL MOISTURE UP AGAINST THE FOOTHILLS ALONG WITH SUBSTANTIAL COOLING ALOFT COULD GENERATE SOME LIGHT SHOWERS FRIDAY NIGHT INTO EARLY SATURDAY. IN ALL CASES AMOUNTS ARE EXPECTED TO BE LIGHT, GENERALLY A TENTH OF AN INCH OR LESS. SATURDAY IS NOW EXPECTED TO BE A DRY DAY FOR MOST AREAS. COULD SEE SOME LINGERING EARLY MORNING PRECIP FOR ERN LA COUNTY VALLEYS/MTNS AS WELL AS THE GRAPEVINE AREA AS NORTHWEST FLOW INCREASES. IN FACT, WITH SNOW LEVELS FALLING RAPIDLY FRIDAY NIGHT THERE COULD BE SOME LIGHT SNOWFALL OVER THE GRAPEVINE THROUGH EARLY SATURDAY MORNING. SHOULD SEE MORE SUNSHINE BY SATURDAY AFTERNOON, THOUGH A COOL NORTHWEST FLOW WILL KEEP TEMPERATURES MAINLY IN THE 50S TO LOWER 60S AT LOWER ELEVATIONS UNDER PARTLY CLOUDY SKIES. LONG TERM...A MUCH TOUGHER FORECAST FOR SUNDAY AS A SECOND STORM SYSTEM DROPS SOUTH ALONG THE WEST COAST. THERE HAVE BEEN FAIRLY LARGE RUN TO RUN CHANGES AND MODEL AGREEMENT AT THIS POINT IS POOR ENOUGH THAT WE ARE STILL IN A SITUATION WHERE THERE IS A RATHER LARGE RANGE OF POSSIBILITIES. THE CANADIAN AND UK SOLUTIONS CONTINUE TO KEEP THE UPPER LOW CLOSER TO THE COAST, KEEPING SO CAL IN A WETTER SCENARIO. HOWEVER, THE ECMWF AND NOW THE GFS ARE TAKING IT FURTHER OFFSHORE. WHILE THE DIFFERENCE BETWEEN THE FARTHEST WEST AND FARTHEST EAST SOLUTIONS MAY ONLY BE A COUPLE HUNDRED MILES OR SO, THIS IS EASILY ENOUGH TO BE THE DIFFERENCE BETWEEN A RAINY DAY AND A DRY ONE. BOTH THE EC AND CANADIAN HAVE BEEN VERY CONSISTENT RUN TO RUN, WHILE THE GFS HAS ONLY RECENTLY BEEN TRENDING WEST AND DRIER. NONE OF THE MODELS ARE SHOWING ANY SIGNIFICANT SOUTHERLY FLOW OR MOISTURE TAP SO THAT'S DIFFERENT FROM THE SYSTEM LAST WEEKEND. PWATS WITH THIS SYSTEM TOP OUT AROUND .8" WHICH IS A GOOD QUARTER INCH LESS THAN LAST WEEKEND. MY INSTINCT IS TO FOLLOW THE DRIER EC/GFS SOLUTIONS, BUT NOT ENOUGH TO MAKE ANY DRAMATIC CHANGES TO POPS AT THIS TIME, ESPECIALLY GIVEN WHAT HAPPENED LAST WEEKEND. I DID LOWER THEM SLIGHTLY FOR SUNDAY, ESPECIALLY SOUTHERN AND EASTERN AREAS. THE UPPER RANGE FOR RAINFALL AMOUNTS WITH THIS SYSTEM WOULD BE A HALF TO ONE INCH, BUT REALISTICALLY IT'S LOOKING CLOSER TO A TENTH TO A HALF. SNOW LEVELS ARE PRETTY LOW, GENERALLY 4000 TO 5000 FEET SUNDAY. THE ECMWF IS A LITTLE SLOWER MOVING THE SYSTEM OUT, BUT MOST AREAS SHOULD SEE A DRYING TREND SUNDAY NIGHT INTO EARLY MONDAY. LIGHT OFFSHORE FLOW AND SUNSHINE SHOULD YIELD A GOOD 5-10 DEGREES OF WARMING MONDAY. THEN CONTINUED RIDGING OVER THE AREA TUESDAY SHOULD BRING ANOTHER FEW DEGREES OF WARMING. THE NEXT SYSTEM WILL START TO APPROACH THE AREA WEDNESDAY. THERE IS A SMALL CHANCE OF PRECIP NORTHERN AREAS WEDNESDAY AFTERNOON BUT A BETTER CHANCE ON THANKSGIVING DAY. && .AVIATION...16/2347Z. NORTH OF POINT CONCEPTION...VFR CONDITIONS WILL PERSIST THROUGHOUT THE PERIOD EXCEPT FOR A CHANCE OF VLIFR TO LIFR CONDITIONS AT KPRB BETWEEN 10Z AND 17Z THURSDAY. SOUTH OF POINT CONCEPTION...THERE IS A CHANCE OF IFR TO MVFR CONDITIONS DEVELOPING BETWEEN 06Z TONIGHT AND 13Z THURSDAY...AND PERSISTING INTO BETWEEN 16Z AND 18Z THURSDAY. HIGHEST CONFIDENCE EXISTS FOR THE COASTAL TERMINALS. KLAX...VFR CONDITIONS SHOULD PERSIST THROUGH AT LEAST 06Z TONIGHT...WITH IFR TO MVFR CONDITIONS DEVELOPING BETWEEN 06Z AND 10Z TONIGHT. HIGHEST CONFIDENCE IN IFR TO MVFR CONDITIONS IS PLACED BETWEEN 11Z AND 14Z THURSDAY. THERE IS A 30 PERCENT CHANCE THAT KLAX COULD REMAIN VFR THROUGHOUT THE PERIOD. KBUR...VFR CONDITIONS ARE EXPECTED THROUGHOUT THE PERIOD...EXCEPT FOR A 20 PERCENT CHANCE OF IFR TO MVFR CONDITIONS BETWEEN 11Z AND 15Z THURSDAY. && .LOX WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY (SEE LAXMWWLOX). && $$ PUBLIC...HALL/WOFFORD AVIATION...HALL SYNOPSIS...B/HALL WWW.WEATHER.GOV/LOSANGELES