Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000 FXUS66 KLOX 260329 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 830 PM PDT FRI JUL 25 2014 .SYNOPSIS... HIGH PRESSURE WILL REMAIN ANCHORED OVER THE DESERT SOUTHWEST THROUGH THE MIDDLE OF NEXT WEEK RESULTING IN CONTINUED SEASONAL TO ABOVE NORMAL TEMPERATURES. HIGH CLOUDS WILL STREAM THROUGH THE AREA WITH A SLIGHT POSSIBILITY OF A THUNDERSTORM OVER THE SAN GABRIELS MAINLY SUNDAY AFTERNOON. OVERNIGHT LOW CLOUDS AND FOG ARE EXPECTED ALONG MOST COASTAL AREAS. && .SHORT TERM (TONIGHT-MON)... SOUTHERN CALIFORNIA WILL REMAIN ON THE WESTERN PERIPHERY OF A LARGE UPPER LEVEL HIGH PRESSURE SYSTEM THAT WILL REMAIN ANCHORED OVER THE DESERTS SOUTHWEST AND TEXAS THROUGH THE WEEKEND. SOME MID LEVEL SUBTROPICAL MOISTURE HAS MOVED INTO SOUTHERN CALIFORNIA TODAY ROTATING AROUND THE PERIPHERY OF THE HIGH PRESSURE SYSTEM. THUNDERSTORM ACTIVITY REMAINED TO OUR SOUTH AND EAST ACROSS SAN DIEGO`S FORECAST AREA...BUT CONSIDERABLE AMOUNT OF MID AND HIGH LEVEL CLOUDS STREAMED INTO LOS ANGELES AND VENTURA COUNTIES. THE INFLUX OF MID AND HIGH LEVEL CLOUDS COMBINED WITH INCREASING ONSHORE FLOW TO BRING COOLING TO MUCH OF THE FORECAST AREA TODAY. IN FACT...SOME OF THE VALLEY AREAS SAW OVER 10 DEGREES OF COOLING FROM YESTERDAY`S SCORCHER. HOWEVER...THE ANTELOPE VALLEY AND A FEW MOUNTAIN LOCATIONS WERE STILL ABLE TO REACH TRIPLE DIGITS TODAY. SIMILAR TEMPERATURES EXPECTED THROUGH THE WEEKEND...WITH A CONTINUATION OF GUSTY ONSHORE WINDS IN THE MOUNTAINS AND DESERTS. STRONGEST WINDS WILL REMAIN FOCUSED ACROSS THE FOOTHILLS OF THE ANTELOPE VALLEY...WHERE GUSTS UP TO 45 MPH CAN BE EXPECTED. IN EVENING UPDATE...HAVE INCREASED MID LEVEL CLOUD COVERAGE A BIT FOR OVERNIGHT INTO SATURDAY...AS LATEST 00Z NAM CONTINUES TO PUMP IN A GOOD AMOUNT OF MID LEVEL MOISTURE FOR AREAS SOUTH OF POINT CONCEPTION. IN FACT...PRECIPITABLE WATER VALUES INCREASE TO 1.2 TO 1.4 INCHES FOR LA/VENTURA COUNTIES ON SATURDAY AFTERNOON. HOWEVER...MODEL SOUNDING SHOWING MOST OF THIS MOISTURE ABOVE THE 700 MB LEVEL...AND TOO MUCH MID LEVEL CLOUDINESS COULD INHIBIT FORMATION OF DEEPER CONVECTION. MODELS SOUNDINGS DID SHOW SOME WEAK CAPE AND INSTABILITY FOR THE LOCAL MOUNTAINS ON SATURDAY AFTERNOON. IN ADDITION...00Z NAM INDCIATED A WEAK VORT MAX ROTATING INTO VENTURA COUNTY ON SATURDAY WHICH WILL HAVE TO BE CLOSELY MONITORED. SO MOST LIKELY WILL SEE SOME AFTERNOON CLOUD BUILDUPS...HOWEVER CANNOT TOTALLY RULE OUT AN ISOLATED STORM. IN EVENING UPDATE...HAVE INCLUDED SOME VERY MINOR THUNDERSTORM POPS OF AROUND 10 PERCENT FOR LOCAL MOUNTAINS ON SATURDAY AFTERNOON. *** FROM PREVIOUS DISCUSSION *** THE ONE HICCUP IN THE PERSISTENCE FORECAST MAY BE SUNDAY AFTERNOON AND EVENING IN THE LA AND VTU COUNTY MOUNTAINS AND THE ANTELOPE VALLEY. SOME INDICATIONS OF SOME CONVECTIVE ACTIVITY THESE AREAS SUNDAY AFTERNOON. CONVECTIVE PARAMETERS NOT OVERLY IMPRESSIVE OTHER THAN MODELS INDICATING A POSSIBLE SHORT WAVE THAT ROTATES AROUND THE SOUTH SIDE OF THE HIGH THEN ROTATES AROUND AND BRUSHES OUR AREA ON SUNDAY. THIS WILL COME INTO BETTER FOCUS WITH NEW MODEL RUNS BUT HAVE KEPT THE GOING FORECAST OF A SLIGHT CHANCE OF THUNDER OVER THE EASTERN SAN GABRIELS FOR NOW. .LONG TERM (TUE-FRI)...THE UPPER LEVEL HIGH OVER THE WESTERN U.S. PERSISTS THROUGH THE LONG TERM. THE ONE CHANGE IS THAT IT PUMPS UP INTO SOUTHWEST CANADA AS OPPOSED TO THE EAST-WEST ELONGATED HIGH THAT IT`S BEEN AS OF LATE. THE ECMWF PUTS THE HIGH AXIS A LITTLE FURTHER WEST...THE RESULT BEING AROUND A 585 DM THICKNESS OVER SOCAL ON WEDN AFTN VERSUS THE 579 DM THICKNESS FORECAST BY THE GFS. THIS WOULD RESULT IN WARMER TEMPS MIDWEEK. DISCOUNTING THE ECMWF FOR NOW IN PART SINCE THE OPERATIONAL GFS IS IN LINE WITH THE GFS ENSEMBLES. SO GOING WITH THE GFS...NOT MUCH CHANGE IN SENSIBLE SURFACE WEATHER FROM DAY TO DAY. TEMPERATURES JUST ABOVE AVERAGE VALLEYS AND DESERT AND AT OR JUST BELOW AVERAGE COASTAL AREAS. ONSHORE GRADIENTS WILL CHANGE LITTLE EACH DAY SO EXPECT SOME OVERNIGHT LOW CLOUDS AND FOG ALONG THE COASTS...BUT AT THIS TIME WITH NOT MUCH INLAND EXTENT. WE APPEAR TO BE RIGHT ON THE WESTERN EDGE OF ANY MONSOONAL FLOW SO DIFFICULT TO TELL AT THIS POINT WHEN WE MAY GET ENOUGH MOISTURE THIS FAR WEST FOR ANY CONVECTIVE ACTIVITY. AT THIS TIME HAVE NOT INCLUDED ANY MENTION OF IT DURING THIS PERIOD. && .AVIATION...25/2340Z... MARINE LAYER CLOUDS EXPECTED TO BE MORE WIDESPREAD TONIGHT ACROSS THE COASTAL PLAIN AS ONSHORE FLOW STRENGTHENS AND MARINE LAYER DEPTH INCREASES. LATEST ACARS DATA SHOWING MARINE LAYER DEPTH AROUND 1000 FEET ACROSS THE LA BASIN LATE THIS AFTERNOON...BUT IS EXPECTED TO DEEPEN TO BETWEEN 1500 AND 1800 FEET BY SATURDAY MORNING. IN 00Z TAF PACKAGE...HAVE MOVED UP TIMING OF IFR/LOW MVFR CIGS ACROSS MANY OF THE COASTAL TAF LOCATIONS...AND KEPT CEILINGS LINGERING TO 18Z-19Z TIME FRAME ON SATURDAY. THERE IS A 20 PERCENT CHANCE THAT IFR CIGS COULD REACH KBUR AND KVNY BY EARLY SATURDAY MORNING. ALSO A 20 PERCENT CHANCE OF CIGS LINGERING INTO THE AFTERNOON HOURS ACROSS COASTAL TAF SITES. KLAX...MODERATE CONFIDENCE IN THE 00Z TAF. LOW MVFR CIGS EXPECTED TO RETURN OVERNIGHT INTO SATURDAY MORNING...BUT THERE IS A 20 PERCENT CHANCE OF CIGS LOWERING INTO IFR CATEGORY BRIEFLY. THERE IS ALSO A 20 PERCENT CHANCE OF MVFR CIGS LINGERING INTO THE AFTERNOON HOURS ON SATURDAY. KBUR...MOSTLY VFR CONDITIONS THROUGH PERIOD...WITH EXCEPTION OF SOME MVFR VSBYS IN HAZE EARLY SATURDAY MORNING. THERE IS A 20 PERCENT CHANCE OF BRIEF IFR CIGS ON SATURDAY MORNING. && .MARINE...25/900 PM. THERE IS A SLIGHT CHANCE OF SHOWER AND THUNDERSTORM DEVELOPMENT ACROSS SOUTHERN COASTAL WATERS BY SUNDAY. OTHERWISE...NO SIGNIFICANT WEATHER IS EXPECTED AT THIS TIME. && .LOX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ PUBLIC...GOMBERG/MJ AVIATION...GOMBERG MARINE...HALL SYNOPSIS...MJ WWW.WEATHER.GOV/LOSANGELES

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