Re: Special Weather Statement

FXUS66 KLOX 060431
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
830 PM PST SAT DEC 5 2009

.SYNOPSIS...
INCREASING ONSHORE FLOW AND A DEEPENING MARINE LAYER COULD PRODUCE
SOME AREAS OF LIGHT SHOWERS SUNDAY...ALONG WITH COLDER TEMPERATURES.
A COLD LOW PRESSURE SYSTEM WILL BRING WINDS...RAIN...AND MOUNTAIN
SNOW ON SUNDAY NIGHT THROUGH EARLY TUESDAY. A SECOND SYSTEM WILL
BRING MOSTLY RAIN TO THE AREA ON WEDNESDAY THROUGH THURSDAY.

&&

.SHORT TERM (TONIGHT-TUE)...DEEPENING MARINE LAYER...GOOD ONSHORE
FLOW AND SOME CYCLONIC FLOW ALOFT HAS HELPED TO EXPAND STRATOCU OVER
MUCH OF THE DISTRICT THIS EVENING. THIS WEATHER PATTERN WILL
CONTINUE TONIGHT WITH PLENTY OF CLOUDINESS FOR MOST AREAS. THERE IS
ALSO A SLIGHT CHANCE OF MAINLY LIGHT SHOWERS OVERNIGHT FOR AREAS S
OF POINT CONCEPTION FROM THE COAST TO THE COASTAL SLOPES.

AN UPPER LEVEL LOW WILL MOVE INTO FAR NORTHERN CA ON SUN...WITH A
BROAD W TO NW FLOW ALOFT OVER SRN CA. THE UPPER TROF WILL MOVE
FURTHER INTO NORTHERN CA SUN NIGHT AND MON WHILE AN ASSOCIATED
RATHER SHARP UPPER LEVEL TROF DEEPENS AND MOVES CLOSE TO THE CENTRAL
CA COAST BY LATE MON. THE TROF WILL MOVE QUICKLY E AND INLAND MON
NIGHT AND INTO THE CENTRAL ROCKIES ON TUE...WHILE A BROAD NW FLOW
ALOFT LINGERS OVER SRN CA. PARTLY TO MOSTLY CLOUDY SKIES WILL
CONTINUE OVER MUCH OF THE FORECAST AREA ON SUN ALONG WITH A SLIGHT
CHANCE OF SHOWERS OVER PORTIONS OF VTU/L.A. COUNTIES.

A STORM SYSTEM WILL APPROACH THE DISTRICT FROM THE E PAC SUN
NIGHT...BRINGING AN INCREASING CHANCE OF RAIN TO THE ENTIRE
DISTRICT. RAIN CAN BE EXPECTED IN ALL AREAS ON MON INTO MON EVENING
AS THE SYSTEM MOVES INTO THE REGION. THE COLD FRONT ASSOCIATED WITH
THE STORM SHOULD PASS THRU THE DISTRICT RATHER QUICKLY LATE MON
AFTERNOON AND EARLY MON EVENING. THE LATEST GFS AND WRF BOTH
CONTINUE TO INDICATE DECENT S TO SE LOWER LEVEL FLOW AHEAD OF THE
FRONT DURING THE DAY MON...ALONG WITH DEEP MOISTURE AND HI OMEGAS.
THE LATEST WRF FORECASTS OMEGAS OVER 40 MICROBARS/SEC OVER A LARGE
PORTION OF SBA/VTU/L.A. COUNTIES JUST AHEAD OF THE FRONT MON
AFTERNOON...WITH A MAX OF 69 MICROBARS/SEC OVER SBA COUNTY. THIS
WOULD INDICATE A PERIOD OF SIGNIFICANT RAINFALL OVER THE SBA S COAST
AND MOUNTAINS AND THRU VTU/L.A. COUNTIES MON AFTERNOON INTO EARLY
MON EVENING...WITH GOOD OROGRAPHIC ENHANCEMENT ON THE S AND SE
FACING SLOPES. THE LATEST RAINFALL ESTIMATES LOOK REASONABLE WITH
.50 AND 1.50 INCHES ACROSS MOST AREAS...AND 1.50 TO 3.00 INCHES
ACROSS SOUTH AND SOUTHWEST FACING FOOTHILL AND MOUNTAIN LOCATIONS.
THE HIGHEST RAINFALL AMOUNTS SHOULD OCCUR ACROSS LOS ANGELES
COUNTY...ESPECIALLY OVER THE SAN GABRIEL MOUNTAINS AND ADJACENT
FOOTHILLS. IT IS LOOKING MORE AND MORE LIKE A FLASH FLOOD WATCH FOR
THE RECENT BURN AREAS WILL BECOME NECESSARY FOR LOCATIONS BELOW THE
SNOW LEVEL.

AS FAR AS SNOW...SIGNIFICANT ACCUMULATIONS WILL BE POSSIBLE AS WELL
ABOVE ABOUT 5000 TO 6000 FEET WITH AMOUNTS OF 6 TO 12 INCHES
EXPECTED WITH HIGHER ACCUMULATIONS UP TO 18 INCHES AT THE HIGHEST
ELEVATIONS. SNOW LEVELS WILL BE DOWN TO NEAR 4000 FEET MON MORNING
AND AGAIN MON EVENING...WITH TRAVEL OVER THE GRAPEVINE POSSIBLY
BEING IMPACTED. THERE IS A WINTER STORM WATCH IN EFFECT FOR THE
MOUNTAINS OF VTU AND L.A. COUNTIES EXCLUDING THE SANTA MONICA RANGE
FROM LATE SUN NIGHT THROUGH TUE MORNING. PLEASE SEE LAXWSWLOX FOR
DETAILS ON THE WINTER STORM WATCH. ALSO...PLEASE SEE THE LATEST
SPECIAL WEATHER STATEMENT (LAXSPSLOX) CONCERNING THE OVERALL IMPACT
FROM THE STORM MONDAY AND ALSO FOR A STORM EXPECTED TO HIT THE AREA
WED INTO THU.

THE STORM WILL EXIT THE REGION BY LATE MON EVENING...WITH ADDITIONAL
SHOWERS AND MOUNTAINS SNOW SHOWERS POSSIBLE ESPECIALLY OVER VTU/L.A.
COUNTIES. SNOW LEVELS WILL DROP QUICKLY MON NIGHT AS WELL...PERHAPS
AS LOW AS 2000 FT...BRINGING THE POSSIBILITY OF SNOW SHOWERS TO THE
FOOTHILL AREAS OF THE ANTELOPE AND CUYAMA VALLEYS...AND THE
FOOTHILLS ADJACENT TO THE SLO INTERIOR VALLEYS. THERE MAY BE A FEW
LINGERING SHOWERS IN A FEW AREAS ON TUE AS WELL...OTHERWISE IT LOOKS
LIKE IT SHOULD BE A MOSTLY DRY DAY ACROSS THE AREA. TEMPS ACROSS THE
REGION WILL BE WELL BELOW NORMAL THRU TUE.

...FROM PREVIOUS DISCUSSION...

.LONG TERM (WED-SAT)...THE NEXT SYSTEM STILL LOOKS ON TRACK FOR WED
NIGHT AND THURSDAY...BUT THERE IS STILL UNCERTAINTY AS TO HOW MUCH
PRECIP WILL RESULT FROM THIS. WITH AMPLE MOISTURE OVER THE PACIFIC
MOSTLY FROM THE REMNANTS OF TYPHOON NIDA...THIS SYSTEM WILL BE MUCH
WARMER AND HAS THE POTENTIAL FOR HEAVY RAINFALL...BUT IT COULD BE
MORE OF A LONG-TERM RAIN MAKER. IT LOOKS LIKE WED THROUGH SAT WILL
HAVE MULTIPLE IMPULSES TO SQUEEZE RAIN OUT OF ALL THE MOISTURE...BUT
THE EXACT TIMING AND AMOUNTS WILL HAVE TO BE WORKED OUT OVER THE
NEXT COUPLE OF DAYS. TEMPERATURES WILL BE UP THANKS TO THE MILDER
AIRMASS WITH THE TROPICAL ORIGINS.

&&

.AVIATION...05/2335Z...MODERATE CONFIDENCE IN THE CURRENT TAF
PACKAGE DUE TO POTENTIAL PROBLEMS WITH CIG HEIGHTS AND COVERAGE OVER
THE REGION. MVFR CIGS SHOULD AFFECT MANY OF THE AIRFIELDS THIS
EVENING THEN SHOULD INCREASE TO VFR CATS OVERNIGHT. TIMING OF THE
INCREASE IN CIGS HEIGHTS COULD BE OFF SOME. SOME MVFR VSBYS WITH
DRIZZLE ALSO NOT OUT OF THE QUESTION AT TIMES TONIGHT FOR
KOXR...KLGB...KLAX...KVNY...AND KBUR.

KLAX AND KBUR...OVERALL MODERATE CONFIDENCE IN THE TAFS DUE TO SOME
UNCERTAINTY IN THE CIGS HEIGHTS AND COVERAGE OVERNIGHT INTO SUN.
MVFR CIGS EARLY THIS EVENING COULD INCREASE TO VFR SOONER THAN
EXPECTED. ALSO...THERE IS A 20 PERCENT CHANCE OF MVFR VSBYS AT TIMES
WITH FOG AND DRIZZLE OVERNIGHT INTO EARLY SUN.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH (SEE LAXWSWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
MARINE WEATHER STATEMENT (SEE LAXMWSLOX).
SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).