451 FXUS66 KLOX 161836 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 1130 AM PDT SAT OCT 16 2010 ***UPDATED AVIATION DISCUSSION*** .SYNOPSIS... A COOL AND MOIST AIR MASS WILL PERSIST OVER SOUTHERN CALIFORNIA THROUGH NEXT WEEK. STRONG ONSHORE FLOW AND A DEEP MARINE LAYER WILL REMAIN OVER THE AREA THROUGH THE WEEKEND. AN AREA OF LOW PRESSURE WILL MOVE OVER THE REGION THROUGH EARLY NEXT WEEK AND BRING A CLOUDY AND UNSETTLED WEATHER PATTERN. && .SHORT TERM (TODAY-MONDAY)... FORECAST IN GOOD SHAPE...WITH ANOTHER COOL AND DRIZZLY DAY. A DEEP MARINE LAYER JUST UNDER 3000 FT CONTINUES TO PUSH STRATUS INTO THE MOUNTAIN SLOPES...WITH SEVERAL REPORTS OF DRIZZLE...AND EVEN A FEW MEASURING. THE FORECAST CHALLENGE OF THE DAY IS WHAT TO DO WITH THE CUTOFF LOW IMPACTING THE AREA EARLY NEXT WEEK. THE PARENT TROUGH IS SHAPING OUT NICELY ABOUT 1000 MI WEST OF SFO. LATEST MODELS ARE PULLING THE LOW A LITTLE MORE OFFSHORE BY MON...WHICH AT THIS POINT STILL WOULD BRING A GOOD SHOT OF RAIN TO THE AREA. IF THE TREND CONTINUES HOWEVER...CHANCES OF RAIN WOULD BE LESS AND DRIER OFFSHORE WOULD BECOME MORE PROBABLE. ***FROM PREVIOUS DISCUSSION*** A BROAD OPEN TROUGH OVER THE EASTERN PACIFIC OCEAN ON WATER VAPOR IMAGERY THIS MORNING WILL BECOME MORE DEVELOPED AS IT PROGRESSES EAST. LATEST MODEL SOLUTIONS AGREE THAT THE AIR MASS WILL REMAIN COOL AND MOIST THROUGH THE WEEKEND WITH THE AIR MASS TURNING MORE UNSTABLE ON SUNDAY OR SUNDAY NIGHT. POPS HAVE BEEN INCREASED AND TRENDED LATER BY ABOUT 6 HOURS LATER AS THE MODELS WILL HAVE SOME DIFFICULTY IN CUTTING OFF THE SYSTEM FROM THE FLOW PATTERN. AS A RESULT...ALL THE DATA IS LIKELY TOO PROGRESSIVE WITH THE MOVEMENT OF THE TROUGH. THE PACKAGE WAS TRENDED THE WAY OF THE NAM-WRF SOLUTION WHICH OFFERS UP THE LEAST PROGRESSIVE SOLUTION. HIGHEST CONFIDENCE OF MEASURABLE RAINFALL IS PLACED BETWEEN SUNDAY NIGHT AND MONDAY NIGHT...BUT THERE WILL LIKELY BE SOME DRIZZLE OVER THE NEXT SEVERAL NIGHT AND MORNINGS AS THE SYSTEM APPROACHES. WITH LITTLE 500 MB COLD ADVECTION OCCURRING AND FAIRLY STABLE 850-500 MB LAPSE RATES IN THE MODEL SOLUTIONS...LOW CONFIDENCE SHOULD BE PLACED IN THE MENTION OF THUNDERSTORMS FOR THE CURRENT TIME. THUNDERSTORMS COULD OCCUR OVER THE AREA AT SOME POINT...MUCH DEPENDING ON HOW CLOSE THE 500 MB COLD POCKET APPROACHES THE COAST. WITH THE LACK OF CONFIDENCE IN THE SIZE...MOVEMENT AND TIMING OF THE SYSTEM...RAINFALL ESTIMATES ARE DIFFICULT TO GET A HANDLE ON AT THIS TIME. BASED UPON THE LATEST MODEL DATA AND TIME OF YEAR...THE BEST GUESS FOR RAINFALL WILL LIKELY FALL BETWEEN 0.10 TO 0.25 INCH ACROSS THE COASTAL AND VALLEY AREAS TO 0.50 TO 1.00 INCH IN THE MOUNTAINS. THE HIGHEST AMOUNTS WILL LIKELY OCCUR ALONG THE SOUTH-FACING SLOPES. .LONG TERM (TUESDAY-FRIDAY)... THE STORM SYSTEM WILL LIKELY LINGER INTO TUESDAY NIGHT AND POSSIBLY INTO WEDNESDAY DEPENDING HOW MUCH THE CUTOFF TROUGH SLOWS. AS A RESULT...THE PACKAGE HAS BEEN TRENDED TOWARDS A SLOWER SOLUTION THAN ECMWF AND GFS SOLUTIONS. SOME CLEARING SHOULD OCCUR FOR LATE WEEK AS WEAK HIGH PRESSURE BUILDS IN OVER THE REGION...BUT ANOTHER STORM SYSTEM COULD APPROACH THE AREA BY THE END OF THE WEEK. && .AVIATION...16/1830Z...LOW TO MODERATE CONFIDENCE WITH 18Z TAFS IN RESPECT TO CIGS. CONTINUING SOME LIFR TO IFR CIGS THROUGH 20Z...BECOMING IFR/MVFR FOR REMAINDER OF THE DAY. 40 PERCENT CHANCE FOR DZ JUST ABOUT ANYWHERE TODAY WEST OF MOUNTAINS IN LA/VTU/SBA COUNTIES. A FEW ELEVATED STRATOCU ACROSS LA/VTU/SBA COUNTY MTNS THROUGH THIS AFTERNOON. NO CLEARING IS EXPECTED ACROSS COASTAL AREAS...WITH A SLIGHT CHANCE THERE WILL BE NO CLEARING ACROSS INLAND SECTIONS IN THE VALLEYS. KLAX...MODERATE CONFIDENCE IN THE TAF. THERE IS A 20 PERCENT CHANCE CIGS COULD SLIP INTO THE IFR CATEGORY BETWEEN 03Z AND 09Z SUNDAY. THERE IS A 20 PERCENT CHANCE THAT CIGS WILL SCATTER OUT BETWEEN 21Z AND 00Z THIS AFTERNOON. KBUR...MODERATE TO HIGH CONFIDENCE IN THE TAF. THERE IS A 20 PERCENT CHANCE THAT CIGS WILL NOT SCATTER OUT UNTIL 22Z THIS AFTERNOON. && .LOX WATCHES/WARNINGS/ADVISORIES... HIGH RIP CURRENT RISK (SEE LAXSRFLOX). && $$ PUBLIC...RK/HALL AVIATION...CAK SYNOPSIS...HALL WWW.WEATHER.GOV/LOSANGELES