091 FXUS66 KLOX 222200 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 200 PM PST SAT NOV 22 2008 .SHORT TERM (TONIGHT THROUGH TUESDAY)...12Z MODELS STILL INDICATE AN UNSETTLED WEEK UPCOMING FOR THE DISTRICT. OVERALL...12Z GFS AND WRF HAVE THE SAME GENERAL IDEA WITH THE SYNOPTIC DETAILS THROUGH TUESDAY...ALTHOUGH TRACK DIFFERENCES DO EXIST. AT UPPER LEVELS...WEAK RIDGE WILL MOVE ACROSS THE AREA ON SUNDAY AS AN UPPER LOW DEVELOPS OVER THE EASTERN PACIFIC. ON MONDAY AND TUESDAY...THE MODELS MOVE THE LOW TOWARDS THE COAST...WITH THE LOW CENTER ABOUT 300 NM WEST OF POINT CONCEPTION. NEAR THE SURFACE... A GENERAL SOUTHEASTERLY FLOW WILL DEVELOP OVER THE AREA ON SUNDAY AND GRADUALLY STRENGTHEN THROUGH TUESDAY. FOR TONIGHT THROUGH MONDAY MORNING...WILL EXPECT A GRADUAL INCREASE IN MARINE LAYER DEPTH AND COVERAGE...WITH RATHER WIDESPREAD LOW CLOUD COVERAGE INTO THE COASTAL VALLEYS BY MONDAY MORNING. WITH THE INCREASE IN MARINE LAYER AND LOWERING H5 HEIGHTS/THICKNESSES COOLER TEMPS CAN BE EXPECTED SUNDAY AND MONDAY AFTERNOON. BY MONDAY AFTERNOON...THE APPROACHING UPPER LOW WILL BEGIN TO BRING A THREAT OF RAIN TO THE AREA. ON MONDAY AFTERNOON...THE SYSTEM WILL BRING A SLIGHT CHANCE OF RAIN TO SLO/SBA COUNTIES... WITH THE RAIN CHANCES INCREASING AND SPREADING SOUTH MONDAY NIGHT AND TUESDAY. AT THIS TIME...WILL MENTION HIGH CHANCE POPS FOR MONDAY NIGHT AND TUESDAY FOR ALL AREAS. THE SOUTHERLY FLOW AHEAD OF THE UPPER LOW WILL LIKELY PRODUCE SOME SIGNIFICANT OROGRAPHIC PRECIP ON SOUTH-FACING SLOPES. THE SOUTHERLY FLOW WILL HELP KEEP SNOW LEVELS AT RATHER HIGH LEVELS THROUGH THE PERIOD...ALTHOUGH BY TUESDAY AFTERNOON...SNOW LEVELS AROUND 6000 FEET ARE NOT OUT OF THE QUESTION. BOTH THE 12Z GFS AND WRF INDICATE SOME SLIGHT INSTABILITY AND THE PRESENCE OF A JET TO OUR SOUTH MONDAY NIGHT AND TUESDAY. WOULD NOT BE SURPRISED TO SEE SOME CONVECTIVE ACTIVITY MONDAY NIGHT/TUESDAY...BUT WILL LET THE NEXT COUPLE OF SHIFTS LOOK AT THE 00Z RUNS TO BETTER DETERMINE THAT POSSIBILITY. ALONG THE PRECIP CHANCES...THIS SYSTEM WILL PRODUCE SOME GUSTY SOUTHEASTERLY WINDS ACROSS THE AREA...ESPECIALLY IN THE MOUNTAINS WHERE GUSTS TO 50 MPH WILL BE POSSIBLE MONDAY NIGHT AND TUESDAY. .LONG TERM (WEDNESDAY THROUGH SATURDAY)...THE UPPER LOW WILL CONTINUE TO AFFECT THE AREA THROUGH WEDNESDAY AFTERNOON...WITH SNOW LEVELS DROPPING TO AROUND 5500 FEET BY WEDNESDAY AFTERNOON. OVERALL...INITIAL RAINFALL ESTIMATES THROUGH WEDNESDAY AFTERNOON FOR THIS STORM WILL RANGE FROM 0.25-1.00" ACROSS COASTAL AREAS WITH 1-2" INCHES IN THE MOUNTAINS...WITH THE HIGHEST TOTALS ON SOUTH-FACING SLOPES. FOR THANKSGIVING THROUGH SATURDAY...THE EXTENDED MODELS CONTINUE TO DIVERGE NOTICEABLY. THE 12Z GFS DROPS ANOTHER UPPER LOW SOUTH ALONG THE CALIFORNIA COAST THURDAY THROUGH SATURDAY...WHILE THE 12Z ECMWF RETROGRADES AN UPPER LOW FROM THE 4-CORNERS SOUTHWEST OVER EXTREME SOUTHERN CALIFORNIA. THE GFS SOLUTION IS A MUCH WETTER SCENARIO THAN THE ECMWF. WITH SUCH MODEL DISCREPANCIES... WILL NOT BITE ONE WAY OR THE OTHER FOR THE END OF THE WEEK. WILL KEEP CURRENT BLANKET PARTLY CLOUDY SKIES AND SLIGHT CHANCE POPS FOR ALL AREAS THANKSGIVING THROUGH SATURDAY AND HOPE FOR BETTER MODEL AGREEMENT WITH FUTURE RUNS. && .AVIATION...22/1800Z UPPER LEVEL LOW CENTERED SOUTH OF THE AREA WILL SHIFT NORTHEAST WHILE A TROUGH OF LOW PRESSURE OVER THE EASTERN PACIFIC DIVES SOUTHEAST. LIGHT UPPER LEVEL SOUTHWEST FLOW OVER THE AREA WILL PREVAIL. A WEAK PRESSURE GRADIENT OVER THE AREA WILL PERSIST. LOW LEVEL SOUTH FLOW WILL PERSIST NEAR SHORE AND LOW CLOUDS SOUTH OF THE AREA WILL DRIFT NORTH OVERNIGHT WITH TOPS AROUND 020. KLAX...THERE IS A CHANCE CIGS WILL DEVELOP INITIALLY BELOW 010 THEN ASCEND TO 015 WITH TOPS AROUND 020 OVERNIGHT THROUGH SUNDAY MORNING. KBUR...THERE IS A CHANCE CIGS WILL DEVELOP BELOW 010 LATE IN THE PERIOD. VIRTUALLY CERTAIN - 95-100% VERY LIKELY - 80-95% LIKELY - 60-80% CHANCE - 30-60% VERY UNLIKELY - 20% OR LESS && .LOX WATCHES/WARNINGS/ADVISORIES... SMALL CRAFT ADVISORY (SEE LAXMWWLOX). && $$ PUBLIC...THOMPSON AVIATION...30 WWW.WEATHER.GOV/LOSANGELES