Iowa Environmental Mesonet
Iowa State University Department of Agronomy
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289 FXUS66 KLOX 270509 AFDLOX SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA 910 PM PST THU NOV 26 2009 .SYNOPSIS... A COLD LOW PRESSURE SYSTEM WILL DROP DOWN INTO OUR AREA BY FRIDAY NIGHT...BRINGING COLDER TEMPERATURES...A CHANCE OF SHOWERS AND POSSIBLY LOW ELEVATION SNOW THROUGH SATURDAY. BEHIND THIS SYSTEM...SUNDAY IS EXPECTED TO BEGIN A MODERATE WARMING TREND WITH OFFSHORE WINDS LASTING INTO MID WEEK. && .SHORT TERM (TONIGHT-SUN)...MOSTLY CLEARS SKIES PREVAILED ACROSS THE DISTRICT THIS EVENING...EXCEPT PATCHY LOW CLOUDS WERE NOTED ALONG THE CENTRAL COAST. SOME OF THESE LOW CLOUDS MAY MOVE INLAND OVER THE CENTRAL COAST TONIGHT...AND SOME HI CLOUDS SHOULD MOVE INTO SLO/SBA COUNTIES AS WELL...OTHERWISE MOSTLY CLEAR SKIES CAN BE EXPECTED FOR MOST AREAS THRU TONIGHT. LOCAL GUSTY NE WINDS WILL CONTINUE OVER PARTS OF VTU/L.A. COUNTIES THIS EVENING AS WELL...BUT WINDS WILL REMAIN WELL BELOW ADVISORY LEVELS. A WEAK UPPER RIDGE OVER SRN CA THIS EVENING WILL BREAK DOWN QUICKLY TONIGHT AS AN UPPER LEVEL TROF OVER THE E PAC APPROACHES THE W COAST. THE UPPER TROF WILL STRENGTHEN INTO AN UPPER LEVEL LOW OVER THE CENTRAL CA COAST BY LATE FRI...THEN THE UPPER LOW WILL DROP SE AND INTO SRN CA LATE FRI NIGHT AND SAT. THE GFS CONTINUES TO BE FURTHER INLAND WITH THIS LOW AS COMPARED WITH THE WRF. THE LATEST WRF TRACKS THE UPPER LOW RIGHT OVER THE L.A. COUNTY COAST BY LATE SAT...WHILE THE GFS POSITIONS THE UPPER LOW CLOSER TO THE ARIZONA BORDER NEAR NEEDLES. BOTH MODELS THEN TRACK THE UPPER LOW S OR SW TO NORTHERN BAJA BY EARLY SUN...AND TO CENTRAL BAJA BY LATE SUN. THE 12Z ECMWF MATCHES UP NICELY WITH THE CURRENT GFS TRACK AND SPEED OF THIS SYSTEM THRU SUN. THERE MAY BE A SHOWER OR TWO FRI AFTERNOON OVER SLO COUNTY... OTHERWISE DRY BUT COOLER WEATHER IS EXPECTED OVER THE FORECAST AREA ON FRI...ALONG WITH GUSTY NW WINDS ALONG THE CENTRAL COAST IN THE AFTERNOON. GUSTY NW TO N CANYON WINDS WILL ALSO BE POSSIBLE ALONG THE SBA S COAST AND MOUNTAINS FRI EVENING...WITH WINDS POSSIBLY REACHING ADVISORY LEVELS. SOME CLOUDINESS WILL START TO MOVE MAINLY INTO SLO/SBA COUNTIES WITH A DYING COLD FRONT DURING THE DAY...WITH MOSTLY SUNNY SKIES EXPECTED ELSEWHERE. HIGHS ARE EXPECTED TO COOL BACK TO NEAR NORMAL TO SLIGHTLY BELOW NORMAL ACROSS THE REGION. AS THE UPPER LOW MOVES IN FRI NIGHT AND SAT...THERE WILL BE A SLIGHT CHANCE TO CHANCE OF SHOWERS AND MOUNTAIN SNOW SHOWERS OVER MUCH OF THE AREA...WITH THE SLIGHT CHANCE LINGERING MAINLY OVER THE MOUNTAINS SAT NIGHT. IF THE UPPER LOW MOVES FURTHER INLAND... HOWEVER...THE BEST CHANCE OF PRECIP WILL BE OVER INLAND PORTIONS OF THE DISTRICT WITH MUCH LOWER POPS ALONG THE COAST AND ADJACENT VALLEYS S OF POINT CONCEPTION. THE WRF FORECAST WOULD ALSO BRING THE POSSIBILITY OF AN ISOLATED THUNDERSTORM TO THE REGION AS WELL...BUT FOR NOW WILL GO WITH A LESS THAN 15 PERCENT CHANCE PENDING FURTHER MODEL RUNS. OVERALL THIS SYSTEM DOES NOT APPEAR TO BE A BIG RAIN PRODUCER WITH GENERALLY A TENTH OF AN INCH OR LESS EXPECTED EXCEPT HIGHER AMOUNTS WOULD NOT BE OUT OF THE QUESTION ON N AND NE FACING MOUNTAIN SLOPES. WITH SNOW LEVELS LOWERING TO NEAR 4000 FEET BY SAT MORNING...SOME SNOW COULD FALL ON THE GRAPEVINE AND AFFECT TRAVEL. PLEASE MONITOR THE LATEST SPECIAL WEATHER STATEMENTS (LAXSPSLOX) FOR UPDATES ON THIS UPCOMING WEATHER SYSTEM. OFFSHORE FLOW IS EXPECTED TO INCREASE OVER THE REGION LATER SAT NIGHT AND SUN AS THE UPPER LOW MOVES TO THE SOUTH OF THE REGION. GUSTY NE CANYON WINDS WILL BE POSSIBLE BELOW AND THRU PASSES AND CANYONS OF L.A./VTU COUNTIES BUT IT APPEARS WINDS SHOULD REMAIN BELOW ADVISORY LEVELS...EXCEPT POSSIBLY AROUND ADVISORY LEVELS AT TIMES IN THE MOUNTAINS SUN MORNING. A FEW LINGERING MOUNTAIN SNOW SHOWERS MAY AFFECT THE L.A. COUNTY MTNS ESPECIALLY ON THE NE SLOPES SUN MORNING...OTHERWISE CLEARING SKIES WITH DRY AND SLIGHTLY WARMER CONDITIONS CAN BE EXPECTED OVER THE REGION ON SUN TO FINISH OFF THE HOLIDAY WEEKEND. ...FROM PREVIOUS DISCUSSION... .LONG TERM (MON-THU)...WARMING TREND TO CONTINUE MONDAY AND TUESDAY UNDER WEAK TO MODERATE OFFSHORE FLOW. AIRMASS DOESN'T WARM UP QUITE AS MUCH AS IT HAS WITH THE CURRENT OFFSHORE EVENT SO HIGHS SHOULD TOP OUT MOSTLY IN THE 70S AT LOWER ELEVATIONS WITH LOCALLY WINDY CONDITIONS BELOW PASSES AND CANYONS. CONFIDENCE IN THE FORECAST BEYOND TUE IS LOW AS THE GFS HAS BEEN GOING BACK AND FORTH BETWEEN A RIDGE ACROSS THE ERN PACIFIC (WHICH IS ALSO INDICATED ON THE ECMWF AND CANADIAN) AND A SEMI-CUTOFF UPPER LOW WITH SOME MOISTURE IN IT. CURRENT FORECAST TRENDS TOWARDS THE MORE CONSISTENT MODELS WHICH KEEP THE AREA DRY WITH ABOVE NORMAL TEMPS THROUGH THU. && .AVIATION...27/0500Z...MODERATE TO HI CONFIDENCE IN THE CURRENT TAFS. SOME LOW CLOUDS AND FOG WITH LIFR AND IFR CONDITIONS SHOULD AFFECT KSMX AND KSBP LATER TONIGHT INTO FRI MORNING...WITH MODERATE CONFIDENCE IN THIS. OTHERWISE VFR CONDITIONS EXPECTED AT THE AIRFIELDS THRU FRI. KLAX...HIGH CONFIDENCE IN CURRENT TAF. KBUR...HIGH CONFIDENCE IN CURRENT TAF. && .LOX WATCHES/WARNINGS/ADVISORIES... SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX). SMALL CRAFT ADVISORY (SEE LAXMWWLOX). HIGH SURF ADVISORY (SEE LAXCFWLOX). && $$ PUBLIC...SIRARD/WOFFORD AVIATION...SIRARD SYNOPSIS...BARTLING WWW.WEATHER.GOV/LOSANGELES