FXUS66 KLOX 241220
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
334 AM PST THU DEC 24 2009

.SYNOPSIS... 
A WEAK UPPER LEVEL RIDGE WILL KEEP DRY WEATHER ACROSS THE AREA 
THROUGH CHRISTMAS WITH NEAR NORMAL TEMPERATURES. A SERIES OF MOSTLY 
WEAK STORM SYSTEMS MOVING THROUGH THE EASTERN PACIFIC WILL BRING A 
SLIGHT CHANCE OF RAIN TO THE REGION LATE SATURDAY OR SATURDAY NIGHT 
THROUGH MONDAY...THEN DRY WEATHER IS EXPECTED AGAIN THROUGH MID WEEK.

&&

.SHORT TERM (TODAY-SAT)...CLEAR SKIES ACROSS THE REGION EARLY THIS 
MORNING. WITH THE LIGHT WINDS AND LITTLE MOISTURE...EXCELLENT 
RADIATIONAL COOLING HAS TAKEN PLACE...AND TEMPS WERE ALREADY 
DROPPING TOWARD THE FREEZING MARK ACROSS THE S CST OF SBA COUNTY AND 
IN THE VLYS OF VTU COUNTY...SO FROST ADVISORIES IN PLACE LOOK GOOD 
FOR THOSE AREAS. THERE LIKELY WILL ALSO BE SOME PATCHY FROST ACROSS 
THE VENTURA COUNTY COASTAL PLAIN...IN THE VALLEYS OF LOS ANGELES 
COUNTY AND IN THE SANTA MONICA RANGE EARLY THIS MORNING...BUT 
PROBABLY NOT WIDESPREAD ENOUGH TO WARRANT ADVISORIES.

AN UPPER RIDGE WILL BUILD ACROSS THE ERN PACIFIC TODAY...THEN THIS 
RIDGE WILL SHIFT SLOWLY EWD INTO CA TONIGHT AND CHRISTMAS...KEEPING 
SKIES MOSTLY CLEAR ACROSS THE REGION. WEAK OFFSHORE LOW LVL FLOW 
WILL PERSIST THROUGH SAT MORNING...BUT EXPECT ONLY LOCALLY GUSTY 
WINDS IN THE MTNS OF L.A. AND VTU COUNTIES. AFTER A COLD START... 
TEMPS WILL WARM SIGNIFICANTLY...AND MAX TEMPS SHOULD BE A FEW 
DEGREES WARMER THAN THEY WERE ON WED IN MOST AREAS. HIGHS WILL 
APPROACH 70 DEGREES IN THE WARMER SECTIONS OF THE CSTL PLAIN AND 
VLYS OF L.A. AND VTU COUNTIES...JUST ABOUT NORMAL FOR THIS TIME OF 
YEAR. DO NOT EXPECT TEMPS TO BE QUITE AS COOL TONIGHT...ALTHOUGH 
FROST ADVISORIES MAY ONCE AGAIN BE NEEDED FOR THE VTU COUNTY VLYS. 
MAX TEMPS ON CHRISTMAS SHOULD BE VERY SIMILAR TO THOSE REACHED TODAY.

AN UPPER TROUGH MOVING INTO THE ERN PACIFIC WILL CAUSE THE RIDGE 
ACROSS THE REGION TO BREAK DOWN AND SHIFT EWD...AND THE WK OFFSHORE 
FLOW WILL FLIP ONSHORE SAT AFTERNOON. MID AND HIGH LVL CLOUDS WILL 
INCREASE ACROSS THE FCST AREA...WITH SKIES BECOMING MOSTLY CLOUDY 
ACROSS FAR NORTHERN SECTIONS. A WEAKENING FRONTAL SYSTEM WILL BRING 
A SLIGHT CHANCE OF RAIN TO SLO COUNTY SATURDAY AFTERNOON. MAX TEMPS 
WILL BE DOWN SEVERAL DEGREES ACROSS THE ENTIRE FCST AREA SAT.

.LONG TERM (SAT NIGHT-WED)...ALTHOUGH THE FRONTAL SYSTEM WILL FALL 
APART...THERE WILL BE A DECENT AMOUNT OF LOW LVL MOISTURE ACRS THE 
AREA SAT NIGHT...SO A SLIGHT CHANCE OF RAIN LOOKS WARRANTED. THE 
FCST GETS TRICKIER FOR SUN THRU MON...AS MODELS CONT TO DISAGREE AND 
CONTINUE TO VACILLATE FROM RUN TO RUN. THE 00Z RUN GFS SHOWED A 
DECENT SLUG OF RAIN SPREADING ACROSS THE FCST AREA LATE SUN OR SUN 
NIGHT INTO EARLY MONDAY AS AN UPPER LOW FORMS AND TRACKS NEAR 
POINT CONCEPTION. THE ECMWF SHOWED A TRACK MUCH FARTHER TO THE S AND 
W WITH THIS SYSTEM...KEEPING THE BULK OF THE RAIN WELL OFFSHORE. THE 
06Z RUN OF THE GFS HAS TRENDED FARTHER S...WITH MODERATE TO POSSIBLY 
HEAVY RAIN JUST OFF THE COAST SUN NIGHT. THE WRF DOES NOT INDICATE
THE FORMATION OF A SOUTHERN UPPER LOW THROUGH 18Z SUNDAY...BUT SHOWS 
A FAIRLY POTENT UPPER LOW OFF THE COAST OF CENTRAL CA...WITH A 
TROUGH EXTENDING SWD AND A DECENT SFC FRONT APCHG THE REGION. FOR 
NOW...WILL MAINTAIN THE CHANCE OF RAIN SUNDAY THROUGH MONDAY...WITH 
THE BEST THREAT OF ANY SIGNIFICANT RAIN SUN NIGHT INTO MONDAY 
MORNING. AFTER THAT A RIDGE IS FCST TO BUILD INTO THE ERN PACIFIC 
TUE AND WED...WITH NWLY FLOW ALOFT LIKELY BRINGING DRY AND COOL 
WEATHER FOR TUE AND WED. 

&&

.AVIATION...24/1140Z.

CLEAR SKIES WITH VFR CONDS WILL PERSIST ACROSS THE REGION THROUGH 
TONIGHT. WEAK TO LOCALLY MODERATE OFFSHORE WINDS WILL CONTINUE 
ACROSS THE MOUNTAINS AND ADJACENT WIND PRONE VALLEYS IN LOS ANGELES 
AND VENTURA COUNTIES TODAY THROUGH THIS EVENING. NOT ANTICIPATING 
ANY MODERATE UDDF AND LLWS TODAY.

KLAX...HIGH CONFIDENCE IN TAF WITH CAVU CONDS.

KBUR...HIGH CONFIDENCE IN TAF WITH CAVU CONDS. 30 PERCENT FOR WEAK 
TO MODERATE LLWS THIS MORNING THROUGH 12Z FRI. 

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY (SEE LAXNPWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).

&&

$$

PUBLIC...BRUNO
AVIATION...KAPLAN
SYNOPSIS...DB

WWW.WEATHER.GOV/LOSANGELES