878 FXUS66 KLOX 031144 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 445 AM PDT SUN OCT 3 2010 NEW AVIATION DISCUSSION .SYNOPSIS... LINGERING MOISTURE WILL KEEP A CHANCE OF SHOWERS AND THUNDERSTORMS ACROSS THE MOUNTAINS...DESERTS AND INTERIOR VALLEYS TODAY. AN UPPER TROUGH WILL BRING COOLING TO THE REGION THROUGH MONDAY...WITH INCREASING LOW CLOUDS AND FOG WEST OF THE MOUNTAINS. AN UPPER LOW DROPPING THROUGH CALIFORNIA WILL BRING AT LEAST A SLIGHT CHANCE OF SHOWERS TO MUCH OF THE REGION MONDAY THROUGH WEDNESDAY...WITH VERY COOL CONDITIONS. A WARMING TREND IS EXPECTED TOWARD THE END OF THE WEEK INTO THE WEEKEND AS A RIDGE BUILDS INTO THE WEST COAST. && .SHORT TERM (TODAY-TUE)...STRATUS FIELD HAS BECOME WELL ESTABLISHED THIS MORNING...WITH LOW CLOUDS/FOG WDSPRD IN JUST ABOUT ALL CSTL AREAS. CLOUDS WERE BEGINNING TO PUSH INTO THE VLYS OF VTU COUNTY...AND WILL LIKELY PUSH INTO THE SAN GABRIEL VALLEY AS WELL. THE MARINE LAYER DEPTH WAS AROUND 800 FEET NEAR LAX...AND WITH A BIT MORE DEEPENING...SOME CLOUDS COULD SPILL INTO SAN FERNANDO VALLEY. THERE COULD BE SOME LOCAL DENSE FOG...MAINLY ACROSS SLO AND SBA COUNTIES....BUT IT SHOULD NOT BECOME WDSPRD ENOUGH TO REQUIRE ADVISORIES. W-E AND N-S GRADS WERE TRENDING ONSHORE THIS MORNING...AND WILL CONTINUE TO DO SO TODAY. IT IS POSSIBLE THAT SOME CLOUDS WILL LINGER AT THE BEACHES TODAY...ESPECIALLY S OF PT CONCEPTION. THERE WILL BE SEVERAL DEGREES OF COOLING ACROSS THE REGION TODAY AS HEIGHTS/THICKNESSES FALL...TEMPS AT 850 AND 950 MB LOWERS...AND ONSHORE GRADS INCREASE. THE UPPER LOW THAT HAS BEEN LINGERING OFF THE COAST FOR THE PAST FEW DAYS WILL OPEN UP AND MOVE ACROSS THE REGION TODAY AS ANOTHER SHORT WAVE PUSHES TOWARD SRN CA. WHILE THE MID LVL FLOW WILL TURN MORE S TO SWLY TODAY...BLV THERE WILL STILL BE ENOUGH MOISTURE AND INSTABILITY FOR A CHANCE OF SHOWERS/TSTMS THIS AFTERNOON AND EVENING ACROSS THE MTNS OF L.A. AND VTU COUNTIES...THE ANTELOPE VALLEY...AND THE MTNS AND INTERIOR VLYS OF SLO AND SBA COUNTIES. MID LVL FLOW IS FCST TO BE STRONGER THAN IT WAS ON SAT...REDUCING THE THREAT OF FLASH FLOODING FROM ANY STORM. THE SHORT WAVE TROUGH APCHG THE W COAST WILL SHARPEN AND DEEPEN TONIGHT. THE WRF SHOWS QUITE A BIT OF DEEPENING OF THE MARINE LAYER...WITH WDSPRD LOW CLOUDS AND FOG IN CSTL AND VLY AREAS TONIGHT...POSSIBLY REACHING THE CSTL SLOPES BY MON MORNING. WITH THE DEEPENING MARINE LAYER...AND SOME DYNAMIC LIFT A LOW AND MID LVLS...THERE COULD BE SOME DRIZZLE OR EVEN SMALL AMOUNTS OF MEASURABLE LIGHT RAIN LATE TONIGHT/MON MORNING...ESPECIALLY IN CSTL...VLY AND FOOTHILL AREAS S OF PT CONCEPTION. WITH THE TROUGH CONTG TO SHARPEN ON MONDAY...AND THE AXIS REMAINING TO THE W OF THE REGION...EXPECT SKIES TO REMAIN MOSTLY CLOUDY. DUE TO THE AMOUNT OF MOISTURE AND SOME LIFT ASSOCD WITH THE TROUGH...HAVE ADDED SLIGHT CHANCE POPS TO MUCH OF THE FCST AREA ON MONDAY. THERE WILL BE SEVERAL MORE DEGREES OF COOLING ACROSS THE REGION ON MONDAY...WITH TEMPS WELL BELOW NORMAL JUST ABOUT EVERYWHERE. THE FORECAST WILL BE RATHER TRICKY THEREAFTER. ALL MODELS SHOW AN UPPER LOW DEVELOPING OVER NRN CA LATE MONDAY...TRACKING SWD INTO THE FCST AREA MON NIGHT AND TUE. ALTHOUGH THE MODELS HAVE BEEN TRENDING FARTHER W WITH THIS SYSTEM...IT STILL TAKES A TRACK OVER LAND...WHICH SHOULD KEEP IT RATHER STARVED FOR MOISTURE. HOWEVER...WITH SUCH HEIGHT FALLS ACROSS THE REGION...AND SOME MOISTURE...BROAD SCALE LIFT AND INSTABILITY...HAVE BROAD BRUSHED THE FCST WITH MOSTLY CLOUDY SKIES FOR MON NIGHT AND TUE...AND HAVE ADDED SLIGHT CHANCE OR CHANCE POPS TO MOST OF THE REGION...WITH THE BETTER CHANCE OF SHOWERS ON TUE. AS IS ALWAYS THE CASE WITH UPPER LOWS...THE THREAT AND COVERAGE OF ANY SHOWERS WILL BE HIGHLY DEPENDENT UPON THE TRACK OF THE SYSTEM...SO THERE IS A GREAT DEAL ON UNCERTAINTY WITH THE SPECIFICS OF THE FCST. .LONG TERM (WED-SAT)...ALL MODELS DISAGREE WITH EACH OTHER REGARDING THE MOVEMENT OF THE UPPER LOW...ALTHOUGH THE ALL DO KEEP IT IN THE VICINITY OF THE FCST AREA THROUGH AT LEAST WED. THE WRF TAKES IT OFF THE CST TUE NIGHT...AND SHOWS IT GATHERING SOME MOISTURE AND SENDING A DECENT AMOUNT OF RAIN (ON THE ORDER OF ONE HALF INCH TO ONE INCH) INTO WRN VTU AND SBA COUNTIES LATE TUE NIGHT/WED MORNING. THE ECMWF AND GFS SHOW THE UPPER LOW REMAINING OVER LAND...WITH LESS MOISTURE...BUT STILL INDICATE AT LEAST A SLIGHT CHANCE OF SHOWERS ACROSS THE REGION TUE NIGHT/WED. AS SUCH...HAVE CONTD A GENERAL BROAD BRUSH FCST WITH A SLIGHT CHANCE/CHANCE OF SHOWERS TUE NIGHT AND WED. IT WILL CERTAINLY NOT BE RAINING ALL THAT TIME...NOR WILL IT NECESSARILY RAIN EVERYWHERE ACROSS THE FCST AREA...BUT THE THREAT WILL EXIST WITH THIS UNSEASONABLY STRONG UPPER LOW SO FAR S ACROSS THE FCST AREA. WHILE THE ECMWF SHOWS THE UPPER LOW WOBBLING NEAR THE FCST AREA INTO THU...THE GFS SHOWS IT PULLING EWD...FOR SOME WARMING AND DRYING. MORE SIGNIFICANT WARMING IS LIKELY FRI AND SAT AS AN UPPER HIGH DEVELOPS OVER THE PAC AND MOVES TOWARD THE W CST. THERE IS A CHANCE THAT LOW LVL FLOW WILL BECOME OFFSHORE...WHICH WOULD ENHANCE WARMING W OF THE MTNS. && .AVIATION... 03/1130Z MARINE LAYER IS 600 FEET DEEP AND IFR/LIFR CIGS COVER MOST COASTAL SITES. THESE CIGS COULD LAST A LITTLE LATER THAN FORECAST. ANOTHER CHANCE OF TSTMS THIS AFTERNOON ACROSS THE MTNS AND DESERTS. A DEEPER VLY PENETRATING MARINE LAYER IS LIKELY TONIGHT. KLAX...FAIR CONFIDENCE IN TAF. CIGS COULD LINGER TO 21Z. EXACT TIMING OF CIG RETURN TIME AND HGT TONIGHT IS PRETTY UNCERTAIN BUT IT IS MOST LIKELY TO COME IN EARLY AND THEN LOWER TO AT LEAST IFR LEVELS. KBUR...GOOD CONFIDENCE IN TAF THROUGH 06Z. LIFR/IFR CIGS WILL DEVELOP TONIGHT AFTER 06Z BUT LOW CONFIDENCE IN PICKING THE CORRECT HOUR OF ARRIVAL. && && .LOX WATCHES/WARNINGS/ADVISORIES... NONE && $$ PUBLIC...BRUNO AVIATION...ASR SYNOPSIS...DB WWW.WEATHER.GOV/LOSANGELES