Frost Advisory 6, NWS Los Angeles, CA

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
310 AM PDT WED OCT 26 2011

.SYNOPSIS...

MODERATE SANTA ANA WINDS ARE EXPECTED TO DEVELOP TODAY AND CONTINUE
THROUGH THURSDAY. GUSTY NORTHEAST WINDS AND VERY DRY CONDITIONS CAN
BE EXPECTED ACROSS THE AREA...ESPECIALLY BELOW PASSES AND CANYONS.
WEAK OFFSHORE WINDS WILL CONTINUE THROUGH THE WEEKEND WITH WARM
TEMPERATURES AND DRY CONDITIONS. LOW PRESSURE WILL MOVE ACROSS THE
WEST COAST EARLY NEXT WEEK...BRINGING COOLER CONDITIONS TO THE AREA.

&&

.SHORT TERM (TODAY-FRI)...OVERALL...00Z MODELS ARE IN VERY GOOD
SYNOPTIC AGREEMENT FOR THE SHORT TERM. AT UPPER LEVELS...RIDGE OFF
THE WEST COAST WILL ALLOW FOR SHARP TROUGH TO DIVE SOUTH ACROSS
THE GREAT BASIN/INTERIOR CALIFORNIA THROUGH THIS EVENING...THEN
THE TROUGH WILL MOVE EAST THURSDAY/FRIDAY AS RIDGE BUILDS OVER THE
AREA. NEAR THE SURFACE...HIGH PRESSURE WILL BUILD INTO THE GREAT
BASIN TODAY/TONIGHT...THEN WILL GRADUALLY WEAKEN THURSDAY/FRIDAY
AND SHIFT EASTWARD.

WITH THIS PATTERN...A MYRIAD OF WEATHER CONCERNS WILL PRESENT
THEMSELVES THROUGH THE PERIOD. THE MOST IMMEDIATE CONCERN WILL BE
THE DEVELOPING OFFSHORE WINDS. AS THE UPPER TROUGH DIVES SOUTHWARD
AND HIGH PRESSURE BUILDS OVER THE GREAT BASIN...THE AREA WILL BE
PRIMED FOR A MODERATE SANTA ANA WIND EVENT. CURRENTLY..NORTHERLY
WINDS ARE BEGINNING TO INCREASE ACROSS THE MOUNTAINS. BY LATE THIS
MORNING...THE WINDS WILL SHIFT TO THE NORTHEAST AND CONTINUE FROM
THE NORTHEAST THROUGH THE REST OF THE PERIOD. AT THIS TIME...THERE
LOOKS TO BE PRETTY GOOD UPPER LEVEL/THERMAL SUPPORT FOR OFFSHORE
WINDS TODAY THROUGH THURSDAY (WRF 30 AGL WINDS BETWEEN 25 AND 35
KNOTS TONIGHT). SO...WILL ANTICIPATE WINDS TO REACH ADVISORY LEVELS
ACROSS THE VENTURA/LA MOUNTAINS LATE THIS MORNING AND CONTINUE
THROUGH THURSDAY AFTERNOON. AS THE PRESSURE GRADIENT INCREASES THIS
AFTERNOON/EVENING...THE ADVISORY-LEVEL WINDS SHOULD FILTER DOWN TO
THE VENTURA/LA VALLEYS AS WELL AS THE SANTA MONICA MOUNTAINS EARLY
THIS EVENING AND CONTINUE THROUGH THURSDAY AFTERNOON. BY THURSDAY
EVENING...THE UPPER SUPPORT WEAKENS AND THE OFFSHORE GRADIENTS RELAX
WHICH WILL RESULT IN WEAKER WINDS. HOWEVER...THERE WILL STILL LIKELY
BE SOME LOCAL NORTHEAST BREEZES THROUGH FRIDAY.

THE NEXT MOST PRESSING CONCERN IS TEMPERATURES. HIGH TEMPS THROUGH
THE PERIOD WILL SHOW A NICE WARMING TREND...WITH A SLIGHT INCREASE
TODAY THEN MORE NOTICEABLE WARMING THURSDAY/FRIDAY AS OFFSHORE
GRADIENTS CONTINUE AND BOUNDARY LAYER WARMS. THE MAIN ISSUE THE NEXT
TWO DAYS WILL BE OVERNIGHT LOWS. AS THE OFFSHORE FLOW KICKS IN...THE
AIR MASS WILL BECOME VERY DRY. COMBINED WITH SOME COLD AIR BEING
ADVECTED INTO INTERIOR SECTIONS BY THE WINDS...WILL EXPECT SOME
BELOW FREEZING TEMPS ACROSS INTERIOR VALLEYS OF SLO/SBA COUNTIES AS
WELL AS THE ANTELOPE VALLEY. WITH THE MORNING FORECAST...WILL ISSUE
A FROST ADVISORY FOR TONIGHT ACROSS SLO/SBA INTERIOR VALLEYS AND
ANTELOPE VALLEY...AND THEN A FREEZE WATCH THURSDAY NIGHT FOR THE
ANTELOPE VALLEY (AS TEMPS WILL LIKELY DIP BELOW 28 DEGREES IN SOME
AREAS).

AS FOR CLOUDS...THE DEVELOPING NORTHERLY FLOW IS STARTING TO SCOUR
OUT THE MARINE LAYER CLOUDS. BY THIS AFTERNOON...WOULD EXPECT
MOST...IF NOT ALL...CLOUDS TO BE GONE WITH CLEAR SKIES PREVAILING
THROUGH FRIDAY.

.LONG TERM (SAT-TUE)...FOR THE EXTENDED...MODELS START OUT IN GOOD
SYNOPTIC AGREEMENT THROUGH ABOUT MONDAY...THEN START TO DIVERGE
QUITE SIGNIFICANTLY. AT UPPER LEVELS...RIDGE WILL PEAK IN STRENGTH
ON SATURDAY...THEN WEAKEN ON SUNDAY AS TROUGH APPROACHES THE PACIFIC
NORTHWEST...AND THEN THE TROUGH MOVES INLAND ACROSS THE PACIFIC
NORTHWEST ON MONDAY. NOW ON TUESDAY...THE GFS AND CANADIAN MOVE THE
TROUGH QUICKLY EASTWARD. HOWEVER THE ECMWF DECIDES TO TAKE THE
TROUGH AND DROP IT SOUTHWARD AS AN INSIDE SLIDER. NEAR THE SURFACE
WEAK DIURNAL FLOW WILL PREVAIL THROUGH SUNDAY (WEAK OFFSHORE
NIGHT/MORNING AND WEAK ONSHORE AFTERNOON/EVENING). ON MONDAY...THE
ONSHORE FLOW WILL BECOME DOMINATE ACROSS THE AREA...AND CONTINUE
WITH A NORTHWEST INFLUENCE ON TUESDAY.

FORECAST WISE...SATURDAY AND SUNDAY WILL BE VERY NICE DAYS. THE
OFFSHORE FLOW SHOULD KEEP THE AREA STRATUS FREE WHILE ALLOWING FOR
SOME VERY NICE TEMPS. ON MONDAY AND TUESDAY...A COOLING TREND SHOULD
DEVELOP FOR ALL AREAS. WITH THE POTENTIAL FOR AN INSIDE SLIDER ON
TUESDAY...WILL HAVE TO MONITOR THE POSSIBILITY OF SOME SHOWERS.
HOWEVER AT THIS TIME...WILL KEEP THE AREA DRY AS THIS IS THE FIRST
ECMWF RUN WITH THIS INSIDE SLIDER. AS FOR WINDS...THERE MAY BE SOME
LIGHT NORTHEAST BREEZES THROUGH/BELOW PASSES AND CANYONS ON SATURDAY
AND SUNDAY...THEN GUSTY ONSHORE WINDS ACROSS THE MOUNTAINS AND
DESERTS ON MONDAY AND TUESDAY.

&&

.AVIATION...26/1200Z.

PREDOMINANTLY VFR CONDITIONS WILL CONTINUE THROUGH 17Z THIS
MORNING...EXCEPT FOR OCCASIONAL IFR TO MVFR CONDITIONS AT COASTAL
AND VALLEY TERMINALS AND VLIFR TO LIFR CONDITIONS AT KPRB. PERIODS
OF MODERATE TO LOCALLY STRONG WIND SHEAR AND TURBULENCE WILL DEVELOP
AT KPMD AND KWJF THIS MORNING...AND AT KBUR...KVNY...KOXR TONIGHT.

KLAX...THERE IS A 30 PERCENT CHANCE OF MVFR CONDITIONS THROUGH 17Z
THIS MORNING...OTHERWISE VFR CONDITIONS WILL BECOME PREDOMINANT. ANY
EAST WINDS WILL LIKELY REMAIN LESS THAN 10 KNOTS TONIGHT.

KBUR...THERE IS A 30 PERCENT CHANCE OF MVFR CONDITIONS THROUGH 15Z
THIS MORNING...OTHERWISE VFR CONDITIONS WILL BECOME PREDOMINANT.
PERIODS OF MODERATE TO OCCASIONALLY STRONG WIND SHEAR AND TURBULENCE
IS EXPECTED BETWEEN 06Z TONIGHT AND 13Z WEDNESDAY.

&&

.FIRE WEATHER...
WITH INCREASES CONFIDENCE IN A MODERATE SANTA ANA WIND EVENT THROUGH
THURSDAY...THERE WILL DEFINITELY BE SIGNIFICANT FIRE WEATHER
CONCERNS THE NEXT COUPLE OF DAYS. CURRENTLY THERE IS A RED FLAG
WARNING IN EFFECT FOR THE VENTURA AND LA MOUNTAINS (EXCLUDING THE
SANTA MONICAS) FROM THIS AFTERNOON THROUGH THURSDAY AFTERNOON. THIS
LOOKS VERY GOOD AS THE RELATIVE HUMIDITY SHOULD DROP TO VERY LOW
LEVELS LATER THIS AFTERNOON (AND REMAIN VERY LOW THROUGH THURSDAY)
WHILE THE WINDS INCREASE TO ADVISORY LEVELS FOR A SUFFICIENT
DURATION. THE MORE TRICKY PART OF THE FORECAST WILL BE THE VALLEYS
AND SANTA MONICA MOUNTAINS. WHILE THESE AREAS WILL EXPERIENCE THE
GUSTY WINDS AND VERY LOW RELATIVE HUMIDITY ALSO...CRITICAL
CONDITIONS MAY OR MAY NOT REACH DURATION THRESHOLDS. THE POTENTIAL
FOR RED FLAG CONDITIONS FOR THESE AREAS WILL HAVE TO BE COORDINATED
AMONG THE LOCAL OFFICES AND FIRE AGENCIES DURING THE DAY SHIFT
TODAY. EITHER WITH OR WITHOUT A RED FLAG WARNING...THE VALLEYS AND
SANTA MONICA MOUNTAINS WILL DEFINITELY HAVE A VERY HEIGHTENED FIRE
WEATHER CONCERN THROUGH THURSDAY.

FROM THURSDAY AFTERNOON THROUGH SATURDAY...WEAK OFFSHORE FLOW WILL
PERSIST ACROSS THE AREA. THE OFFSHORE WINDS WILL BE MUCH WEAKER.
HOWEVER...THE VERY DRY AIR MASS WILL REMAIN IN PLACE. SO...A
HEIGHTENED FIRE WEATHER CONCERN WILL CONTINUE THROUGH SATURDAY.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING (SEE LAXRFWLOX).
FREEZE WATCH (SEE LAXNPWLOX).
FROST ADVISORY (SEE LAXNPWLOX).
SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).

&&

PUBLIC...THOMPSON
AVIATION...HALL
SYNOPSIS...RAT

WWW.WEATHER.GOV/LOSANGELES

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
403 PM PDT TUE OCT 25 2011

CAZ034>041-044>046-051>054-059-087-088-547-548-261300-
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-
403 PM PDT TUE OCT 25 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHWESTERN CALIFORNIA.

.DAY ONE... TODAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

* SPECIAL WEATHER STATEMENT..SEE WWUS86 KLOX - SPSLOX FOR DETAILS *

.DAYS TWO THROUGH SEVEN... WEDNESDAY THROUGH MONDAY

FROM WEDNESDAY AFTERNOON THROUGH THURSDAY MORNING...THERE WILL BE A
MODERATE SANTA ANA WIND EVENT. GUSTY OFFSHORE WINDS WILL MOSTLY BE
FOCUSED BELOW AND THROUGH PASSES AND CANYONS OF LOS ANGELES AND
VENTURA COUNTIES. WITH THE OFFSHORE WINDS... HUMIDITIES WILL FALL
INTO SINGLE DIGITS ACROSS INLAND PORTIONS OF SOUTHERN CALIFORNIA
WEDNESDAY AFTERNOON INTO THURSDAY. WHILE OFFSHORE WINDS ARE EXPECTED
TO DIMINISH LATE THURSDAY...A VERY DRY AND WARM AIR MASS WILL LIKELY
LINGER INTO THE WEEKEND. A RED FLAG WARNING HAS BEEN ISSUED FOR THE
MOUNTAINS OF LOS ANGELES AND VENTURA COUNTIES DUE TO THIS OFFSHORE
WIND EVENT AND LOWER RELATIVE HUMIDITIES EXPECTED FOR WEDNESDAY
AFTERNOON THROUGH THURSDAY AFTERNOON. THE GREATEST CONCERN IS IN THE
MOUNTAINS...WHERE THE STRONGEST AND LONGER DURATION WINDS ARE
EXPECTED. THE INFLUX OF VERY DRY AIR WILL ALLOW MUCH COLDER
TEMPERATURES ON WEDNESDAY AND THURSDAY NIGHTS ACROSS ACROSS WIND
PROTECTEDPORTIONS OF THE MOUNTAINS...ANTELOPE VALLEY...AND INTERIOR
VALLEYSOF SAN LUIS OBISPO AND SANTA BARBARA COUNTIES. THERE IS THE
POTENTIAL FOR TEMPERATURES TO APPROACH THE FREEZING MARK IN THE
ANTELOPE VALLEY.

* RED FLAG WARNING...........SEE WWUS86 KLOX - RFWLOX FOR DETAILS *

* SPECIAL WEATHER STATEMENT..SEE WWUS86 KLOX - SPSLOX FOR DETAILS *

.SPOTTER INFORMATION STATEMENT...

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

KAPLAN