Frost Advisory 17, NWS Los Angeles, CA

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
230 PM PST TUE DEC 18 2012

.SYNOPSIS...

IN THE WAKE OF AN EXITING COLD FRONT...COLD AND WINDY CONDITIONS WILL
DEVELOP ACROSS THE SOUTHLAND THROUGH WEDNESDAY. ISOLATED SHOWERS
WILL CONTINUE ACROSS PORTIONS OF LOS ANGELES AND VENTURA COUNTIES THROUGH
THSI EVENING. SOME INTERIOR SECTIONS WILL SEE SUB-FREEZING
TEMPERATURES BOTH TONIGHT AND WEDNESDAY NIGHT. CONDITIONS WILL
REMAIN DRY WEDNESDAY INTO THURSDAY WITH ANOTHER CHANCE OF RAIN FOR
NORTHERN AREAS BY FRIDAY...WITH RAIN CHANCE SPREADING SOUTH OVER THE
WEEKEND.

&&

.SHORT TERM (TONIGHT-FRI)...
MAIN COLD FRONT HAS SHIFTED WELL EAST OF FORECAST AREA THIS
AFTERNOON...HOWEVER COLD AND VIGOROUS UPPER LEVEL TROUGH MOVING
THROUGH THE REGION. DOPPLER RADAR INDICATING SCATTERED SHOWER
ACTIVITY ACROSS THE MOUNTAINS AND VALLEYS OF LOS ANGELES AND
VENTURA COUNTIES. THESE AREAS WILL REMAIN VULNERABLE TO SCATTERED
SHOWERS THROUGH EARLY EVENING AS THERE WILL STILL BE SOME GOOD PVA AND
CYCLONIC FLOW FOR THE NEXT 3 TO 6 HOURS. IN ADDITION...GOOD AMOUNT
OF LOW LEVEL MOISTURE AND SOME INSTABILITY ASSOCIATED WITH COLDER
AIR ALOFT AND HEATING NEAR THE SURFACE. BRIEF HEAVY DOWNPOURS AND
SMALL HAIL WILL BE POSSIBLE WITH THE SHOWER ACTIVITY.
MEANWHILE...THE REMAINDER OF THE FORECAST AREA SEEING DRYING
CONDITIONS AS SUBSIDENCE INCREASES ON THE BACK SIDE OF THE UPPER
TROUGH.

THE MAIN IMPACTS OF THIS CURRENT WEATHER SYSTEM WILL CONTINUE TO BE
STRONG WINDS AND COLD TEMPERATURES. ALREADY SEEING A MARKED INCREASE
IN WIND SPEEDS ACROSS THE FORECAST AREA THIS AFTERNOON AS THE LOW
LEVEL FLOW REMAINS WEST TO NORTHWEST. THE LOW LEVEL FLOW WILL
GRADUALLY SHIFT TO A MORE NORTHERLY DIRECTION THIS EVENING...WITH
INCREASING UPPER LEVEL WINDS...SUBSIDENCE...AND COLD AIR ADVECTION.
PEAK UPPER LEVEL WIND SUPPORT AND SUBSIDENCE EXPECTED TO OCCUR
BETWEEN 03Z-09Z TONIGHT. HIGH WIND WARNINGS IN EFFECT FOR THE
MOUNTAINS TONIGHT...WHERE DAMAGING WIND GUSTS UP TO 65 MPH CAN BE
EXPECTED ACROSS THE INTERSTATE 5 CORRIDOR AND SANTA YNEZ
MOUNTAINS...ESPECIALLY NEAR MONTECITO HILLS. THIS WILL
LIKELY BE A WIDESPREAD STRONG WIND EVENT...WITH THE NORTHERLY WINDS
EXPECTED TO FILTER INTO THE TYPICAL NORTH-SOUTH CORRIDORS SUCH AS THE
SANTA CLARITA VALLEY...SAN FERNANDO VALLEY...SANTA MONICA
MOUNTAINS...AND WESTERN PORTIONS OF THE LA COUNTY COAST (ESPECIALLY
NEAR THE 405 CORRIDOR AND HOLLYWOOD HILLS). ALL OF THESE AREAS COULD SEE
GUSTS IN THE 45 TO 50 MPH RANGE...CAPABLE OF DOWNING TREES AND
BRANCHES...ESPECIALLY WITH RECENTLY WET SOILS. IN ADDITION...THERE WILL
BE SUFFICIENTLY STRONG UPPER LEVEL WINDS AND SUBSIDENCE TO GENERATE
A RARE STRONG WIND EVENT ACROSS THE OJAI/LAKE CASITAS AREA...AS WELL AS
PORTIONS OF THE SAN GABRIEL VALLEY.

THE LOW LEVEL FLOW WILL BECOME NORTHEASTERLY ON WEDNESDAY...SETTING THE
STAGE FOR A COLD SANTA ANA WIND EVENT. WITH AFTERNOON FORECAST...HAVE
EXTENDED WIND ADVISORIES FOR TYPICAL WIND PRONE VALLEYS OF LA/VTU COUNTIES
THROUGH 2 PM WEDNESDAY.

OTHER MAJOR SHORT TERM CONCERN WILL BE COLD TEMPERATURES. SIGNIFICANT
INFLUX OF COLD AIR MOVING INTO SOUTHERN CALIFORNIA TONIGHT AS
EVIDENT BY 850 MB TEMPERATURES FALLING AS LOW AS -6 DEGREES CELSIUS
NEAR THE GRAPEVINE...ALONG WITH SUB-ZERO 950 MB TEMPERATURES SPREADING
AS FAR SOUTH AS THE SANTA CLARITA VALLEY. NORMALLY THESE TYPES OF
NUMBERS WOULD REPRESENT A WIDESPREAD FROST AND FREEZE SITUATION FOR THE
SOUTHLAND. HOWEVER...WITH THE STRONG WINDS EXPECTED ACROSS MUCH OF THE
FORECAST AREA TONIGHT...FROST AND FREEZE POTENTIAL WILL REMAIN MORE LOCALIZED
TO WIND SHELTERED LOCATIONS. A FREEZE WARNING HAS BEEN POSTED FOR THE
CUYAMA VALLEY...WHERE HARD FREEZE CONDITIONS CAN BE EXPECTED SHORTLY BEFORE
SUNRISE. ALSO...A FROST ADVISORY HAS BEEN POSTED FOR THE SANTA YNEZ
VALLEY. VERY COLD TEMPERATURES INTO THE 20S CAN ALSO BE EXPECTED FOR THE
ANTELOPE VALLEY AND INTERIOR VALLEYS OF SLO COUNTY...HOWEVER THESE AREAS
HAVE ALREADY SEEN 2 OR MORE NIGHTS OF HARD FREEZE CONDITIONS THIS
SEASON. AS THE AIR MASS CONTINUES TO DRY OUT AND WINDS
DIMINISH...THERE WILL BE THE POTENTIAL FOR EVEN COLDER TEMPERATURES IN
MANY AREAS ON WEDNESDAY NIGHT. AS WE DRAW CLOSER...FROST ADVISORIES
MAY NEED TO BE POSTED FOR PORTIONS OF LA/VTU COUNTY COASTAL AND
VALLEY AREAS.

DRY CONDITIONS ON TAP FOR WEDNESDAY AND THURSDAY...THEN LEADING EDGE
OF NEXT SYSTEM WILL BRING A CHANCE OF LIGHT RAIN TO AREAS NORTH OF
POINT CONCEPTION ON FRIDAY.

.LONG TERM (SAT-TUE)...
MDLS ARE IN A LITTLE BETTER AGREEMENT FOR THE WEEKEND BUT STILL ARE
SHOWING SOME DIFFERENCES AND RUN TO RUN INCONSTANCY SO HAVE KEPT
POPS IN ACROSS THE ENTIRE PERIOD. THATS MORE A REFLECTION ON TIMING
UNCERTAINTY AND DO NOT THINK IN THE LEAST THAT THE WHOLE WEEKEND IS
GOING TO BE A WASH.  BROAD CYCLONIC FLOW WILL KEEP COOL AND MOIST
CONDITIONS GOING THROUGH CHRISTMAS EVE WITH A SLIGHT CHANCE OF SHOWERS.
AT THIS POINT...GFS AND ECMWF BOTH AGREE ON A DRY CHRISTMAS DAY
SOLUTION.

&&

.AVIATION...18/1800Z.

MID/UPPER LEVEL TROUGH OF LOW PRESSURE OVER THE AREA WILL SHIFT
EAST. UPPER LEVEL STRONG SOUTHWEST WINDS WILL BECOME STRONG
NORTHWEST AFTER 19/06Z AND MODERATE WEST AFTER 19/17Z WHILE MID
LEVEL MODERATE WEST WINDS BECOME MODERATE TO STRONG NORTHWEST AFTER
19/03Z THEN LIGHT NORTH AFTER 19/17Z. A SURFACE FRONT WAS SOUTH OF
SANTA CATALINA ISLAND WILL CONTINUE TO MOVE SOUTH AND LOW LEVEL
MOISTURE WILL DIMINISH. FREEZING LEVEL WAS AROUND 6.5KFT THIS MORNING
AND WILL DIFFER BY MINUS 2KFT AFTER 19/04Z THEN ASCEND PLUS 6KFT
AFTER 19/17Z.

KLAX...LOW LEVEL...AT APPROXIMATELY 009...WINDS 34030KT BETWEEN
19/04-19/12Z. OTHERWISE CHANCE BKN 060 THROUGH 18/20Z THEN SKC.

KBUR...CHANCE CIGS 025 THROUGH 18/20Z. OTHERWISE SURFACE WINDS
34020G27KT LIKELY BETWEEN 19/02-19/10Z THEN CHANCE LOW LEVEL...AT
APPROXIMATELY 015...WINDS 01030KT.

&&

.MARINE...NORTHWEST GALES ARE EXPECTED DIMINISH AND BECOME NORTH
TONIGHT AND THEN NORTHEAST WEDNESDAY AS A RIDGE OF HIGH PRESSURE
WEAKENS AND SHIFTS SOUTH AS WELL AS INLAND. AS THE WINDS DIMINISH
THE HAZARDOUS SURF AND STRONG RIP CURRENTS WILL SUBSIDE OVERNIGHT
SOUTH OF POINT CONCEPTION. HIGH SURF ON EXPOSED WEST AND NORTHWEST
FACING SHORES NORTH OF POINT CONCEPTION THIS AFTERNOON MAY SUBSIDE
ALONG THE WEST FACING SHORES TONIGHT THOUGH PERSIST ALONG THE
NORTHWEST FACING SHORES THROUGH WEDNESDAY AFTERNOON AS SWELLS
ORIGINATING FROM THE CENTRAL-EASTERN GULF OF ALASKA...ON MONDAY
NIGHT...BEGIN TO ARRIVE EARLY WEDNESDAY MORNING.  GUIDANCE WAS
CONSISTENT WITH PREVIOUS RUNS AND A 968MB LOW PRESSURE SYSTEM
DEVELOPS WITH STORM FORCE WINDS ORIENTED WITHIN A FETCH BETWEEN
300-310 RELATIVE TO SOUTHWEST CALIFORNIA TONIGHT THROUGH WEDNESDAY
MORNING. THE NORTHWEST SWELLS WILL BEGIN TO ARRIVE EARLY FRIDAY
MORNING AND HIGH SURF AND STRONG RIP CURRENTS WILL LIKELY BUILD AND
PEAK FRIDAY NIGHT AND PERSIST THROUGH SATURDAY NIGHT ALONG ALL
EXPOSED WEST AND NORTHWEST FACING SHORES.  THE TIDE WILL RANGE FROM
AROUND 1 FOOT LATE FRIDAY MORNING TO AROUND 3 FEET EARLY FRIDAY
EVENING AND TO AROUND 5 FEET EARLY SATURDAY MORNING.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING (SEE LAXNPWLOX).
WIND ADVISORY (SEE LAXNPWLOX).
GALE WARNING (SEE LAXMWWLOX).
HIGH RIP CURRENT RISK (SEE LAXSRFLOX).
HIGH SURF ADVISORY (SEE LAXCFWLOX).

&&

PUBLIC...GOMBERG
AVIATION/MARINE...30
SYNOPSIS...SWEET

WWW.WEATHER.GOV/LOSANGELES

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
746 AM PST TUE DEC 18 2012

CAZ034>041-044>046-051>054-059-087-088-547-548-191400-
SAN LUIS OBISPO COUNTY CENTRAL COAST-
SANTA BARBARA COUNTY CENTRAL COAST-SANTA YNEZ VALLEY-
SAN LUIS OBISPO COUNTY INTERIOR VALLEYS-CUYAMA VALLEY-
SANTA BARBARA COUNTY SOUTH COAST-VENTURA COUNTY COAST-
LOS ANGELES COUNTY COAST INCLUDING DOWNTOWN LOS ANGELES-
VENTURA COUNTY INTERIOR VALLEYS-VENTURA COUNTY COASTAL VALLEYS-
SANTA MONICA MOUNTAINS RECREATIONAL AREA-
SAN LUIS OBISPO COUNTY MOUNTAINS-
SANTA BARBARA COUNTY MOUNTAINS-VENTURA COUNTY MOUNTAINS-
LOS ANGELES COUNTY MOUNTAINS EXCLUDING THE SANTA MONICA RANGE-
ANTELOPE VALLEY-CATALINA ISLAND-SANTA CLARITA VALLEY-
LOS ANGELES COUNTY SAN FERNANDO VALLEY-
LOS ANGELES COUNTY SAN GABRIEL VALLEY-
746 AM PST TUE DEC 18 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHWESTERN CALIFORNIA.

.DAY ONE... TODAY AND TONIGHT

AFTER SOME LIGHT MORNING RAIN SHOWERS STRONG NORTHWEST WINDS WILL
BUILD INTO THE AREA. THE MOUNTAINS WILL SEE HAZARDOUS WIND GUSTS AS
HIGH AS 65 MPH. THE VALLEYS WILL SEE GUSTS BETWEEN 45 AND 50 MPH.
THERE WILL BE CLOUDS AND SNOW SHOWERS ACROSS THE GRAPEVINE AREA THIS
AFTERNOON AND EVENING. MARINERS WILL FACE GALE FORCE WINDS BOTH IN
THE INNER AND OUTER WATERS TODAY AND THIS EVENING. HIGH SURF
ADVISORY IS IN EFFECT ON THE CENTRAL COAST. AND THERE WILL ALSO BE A
HEIGHTENED RIP CURRENT RISK IN THE SURF ZONE ALONG THE ENTIRE COAST.

* HIGH WIND WARNING..........SEE WWUS76 KLOX - NPWLOX FOR DETAILS *

* WIND ADVISORY..............SEE WWUS76 KLOX - NPWLOX FOR DETAILS *

* GALE WARNING...............SEE WHUS76 KLOX - MWWLOX FOR DETAILS *

* HIGH SURF ADVISORY.........SEE WHUS46 KLOX - CFWLOX FOR DETAILS *

* HIGH RIP CURRENT RISK......SEE FZUS56 KLOX - SRFLOX FOR DETAILS *

.DAYS TWO THROUGH SEVEN... WEDNESDAY THROUGH MONDAY

STRONG AND HAZARDOUS WINDS WILL CONTINUE INTO WEDNESDAY MORNING. THE
WINDS WILL BE STRONGEST IN THE MOUNTAINS. MOST INTERIOR AREAS WILL
SEE FREEZING TEMPERATURES FOR A FEW HOURS EARLY THURSDAY MORNING.
MORE RAIN IS ON ITS WAY FOR THE WEEKEND.

* HIGH WIND WARNING..........SEE WWUS76 KLOX - NPWLOX FOR DETAILS *

* WIND ADVISORY..............SEE WWUS76 KLOX - NPWLOX FOR DETAILS *

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.