FXUS66 KLOX 250502
AFDLOX
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
900 PM PST THU DEC 24 2009
.SYNOPSIS...
A WEAK UPPER LEVEL RIDGE WILL KEEP DRY WEATHER ACROSS THE AREA
THROUGH SATURDAY WITH COLD OVERNIGHT TEMPERATURES AND NEAR NORMAL
DAYTIME HIGH TEMPERATURES. A SERIES OF WEAK STORM SYSTEMS MOVING
THROUGH THE EASTERN PACIFIC WILL BRING A SLIGHT CHANCE OF RAIN TO
THE REGION SATURDAY NIGHT THROUGH MONDAY...THEN DRY WEATHER IS
EXPECTED AGAIN THROUGH NEW YEARS DAY.
&&
.SHORT TERM (TONIGHT-SUN)...MOSTLY CLEAR SKIES COVERED THE DISTRICT
THIS EVENING...WHICH WILL CONTINUE OVERNIGHT ALTHO SOME HIGH CLOUDS
CAN BE EXPECTED AT TIMES. LOCAL GUSTY NE CANYON WINDS CAN BE
EXPECTED OVERNIGHT AS WELL...MAINLY OVER THE VTU/L.A. COUNTY MTNS
AND FOOTHILLS. HOWEVER...WINDS IN ALL AREAS WILL REMAIN BELOW
ADVISORY LEVELS TONIGHT. IT LOOKS LIKE AREAS OF FROST WILL BE
POSSIBLE LATER TONIGHT IN THE WIND SHELTERED LOCATIONS OF THE VTU
COUNTY VALLEYS...AND THE SANTA MONICA MTNS...WHERE A FROST ADVISORY
IS IN EFFECT. DEWPOINTS HAVE COME UP FAIRLY SIGNIFICANTLY ALONG THE
SBA S COAST...SO ONLY PATCHY FROST IS EXPECTED THERE LATE TONIGHT.
THE FROST ADVISORY FOR THE SBA S COAST WILL BE CANCELLED SHORTLY.
AN UPPER LEVEL RIDGE JUST OFF THE CA COAST THIS EVENING IS FORECAST
TO MOVE INLAND OVER THE STATE ON CHRISTMAS DAY AND FRIDAY
NIGHT...THEN AN UPPER LEVEL TROF WILL MOVE OUT OF THE E PAC AND INTO
MUCH OF THE STATE ON SAT. THE MODELS DIFFER IN THE FINER DETAILS OF
THE UPPER LEVEL PATTERN SAT NIGHT AND SUN...BUT OVERALL IT LOOKS
LIKE SOME UPPER TROFFINESS WILL LINGER OVER THE FORECAST AREA SAT
NIGHT WITH WEAK UPPER LEVEL RIDGING DEVELOPING ON SUN IN RESPONSE TO
AN APPROACHING UPPER LEVEL LOW PRESSURE AREA. A DISSIPATING COLD
FRONT IS EXPECTED TO MOVE INTO SLO/SBA COUNTIES SAT AFTERNOON...
BRINGING A SLIGHT CHANCE OF SHOWERS MAINLY TO PORTIONS OF SLO
COUNTY. THE SLIGHT CHANCE OF SHOWERS SHOULD SPREAD TO MUCH OF THE
FORECAST AREA SAT NIGHT AS A MOIST LOW LEVEL FLOW PERSISTS WITH THE
WEAK UPPER TROFFINESS. AT THIS TIME THE FORECAST FOR SUN IS RATHER
LOW CONFIDENCE DEPENDING ON THE POSITION OF THE UPPER LOW OFF THE
COAST. THE WRF BRINGS IT CLOSER TO THE REGION BY LATE SUN AS
COMPARED TO THE GFS...WHICH RESULTS IN A BETTER CHANCE OF RAIN AND
HIGHER ELEVATION SNOW ACROSS MUCH OF THE AREA. EVEN SO...THE BEST
CHANCES OF PRECIP LOOK LIKE IT WILL BE OVER SLO/SBA COUNTIES WITH
PERHAPS ONLY 15-20 PERCENT CHANCE ELSEWHERE. WEAK OFFSHORE FLOW OVER
THE DISTRICT CAN BE EXPECTED MAINLY NIGHT AND MORNING HOURS INTO
EARLY SAT...THEN THE FLOW WILL TURN MORE SE TO S LATER SAT NIGHT
INTO SUN. FAIR SKIES WILL CONTINUE INTO FRI NIGHT...WITH INCREASING
AMOUNTS OF CLOUDS EXPECTED OVER THE WEEKEND. TEMPS ACROSS THE REGION
ARE EXPECTED TO BE NEAR NORMAL ON FRI THEN COOL TO SLIGHTLY BELOW
NORMAL SAT AND 4-8 DEG BELOW NORMAL FOR SUN.
...FROM PREVIOUS DISCUSSION...
.LONG TERM (SUN NIGHT-THU)...SIGNIFICANT VARIATIONS EXIST BETWEEN
THE EXTENDED MODELS REGARDING NEXT SYSTEM FOR SUNDAY NIGHT INTO
MONDAY. 12Z ECMWF TAKES THIS SYSTEM WELL SOUTH AND BRINGS ABSOLUTELY
NO PRECIPITATION TO SOUTHERN CA. 12Z GFS AND CANADIAN MODELS ARE
MORE CONSISTENT AND FURTHER NORTH WITH PRECIPITATION ALONG AND JUST
OFF THE SOUTHERN CA COAST. PREFER THIS LATTER SOLUTION AS IT IS MORE
CONSISTENT FROM EARLIER RUNS AND MUCH MORE IN LINE WITH OFFICIAL
FORECASTS. THUS HAVE MADE ONLY MINOR CHANGES TO FORECASTS...MAINLY
TO FOCUS POPS AND PRECIPITATION CLOSER TO THE COAST. LATER SHIFTS
CAN STILL ADJUST AND FINE TUNE AMOUNTS. TUESDAY THROUGH THURSDAY
A RIDGE IS STILL FORECAST TO BUILD INTO THE EASTERN PACIFIC WITH
NORTHWESTERLY FLOW ALOFT LIKELY BRINGING DRY AND COOL WEATHER.
&&
.AVIATION...24/2328Z...HI CONFIDENCE IN CURRENT TAF PACKAGE.
KLAX AND KBUR...HI CONFIDENCE IN CURRENT TAFS.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY (SEE LAXNPWLOX).
&&
$$
PUBLIC...SIRARD/TRM
AVIATION...SIRARD
SYNOPSIS...TRM
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