Freeze Warning 5, NWS Los Angeles, CA

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
327 AM PST SAT DEC 3 2011

.SYNOPSIS...

STRONG OFFSHORE FLOW WITH PERIODS OF GUSTY SANTA ANA WINDS WILL
CONTINUE THROUGH TUESDAY. OFFSHORE FLOW WILL WEAKEN FOR THE MIDDLE
PORTION OF NEXT WEEK...ALLOWING FOR WARMER DAYS BUT CONTINUED
COOL NIGHTS. A DRY WEATHER PATTERN WILL PERSIST THROUGH LATE NEXT
WEEK.

&&

.SHORT TERM (TODAY-TUESDAY)...

THE LATEST WATER VAPOR IMAGERY INDICATES A COLD TROUGH OF LOW
PRESSURE DROPPING SOUTH INTO THE LOWER COLORADO RIVER
BASIN...WITH AN AREA OF SUBSIDENT AIR DEVELOPING OVER THE OWENS
VALLEY BEHIND A COLD FRONT. WITH THE COLD AND SUBSIDENT AIR MASS
DEVELOPING...OFFSHORE WINDS SHOULD INCREASE ONCE AGAIN THIS
MORNING. THE COLD AIR MASS SHOULD SLAM UP AGAINST THE INTERIOR
SLOPES OF THE MOUNTAINS BETWEEN 12Z AND 15Z...OR BETWEEN 4 AM AND
7 AM LOCAL TIME. NAM-WRF 850 MB THERMAL GRADIENTS ACROSS THE SAN
GABRIEL RANGE APPROACH -6 DEGREES CELSIUS....WITH AROUND 50 KNOTS
OF WIND. WIND HEADLINES HAVE BEEN CONTINUED...BUT THERE IS A
CHANCE THAT WINDS GUSTS APPROACH DAMAGING LEVELS IN THE SANTA
MONICA MOUNTAINS. LOCAL 4-KM WRF SOLUTIONS INDICATE 55 KNOTS
OCCURRING AT 950 MB BETWEEN 13Z AND 18Z. WITH WINDS STILL SLOW TO
INCREASE THIS MORNING...WORDING OF ISOLATED GUSTS TO 65 MPH WILL
ADDED...BUT A WIND ADVISORY WILL BE LEFT INTACT FOR NOW.

IN WIND-SHELTERED AREAS...A DRY AIR MASS IS ALLOWING RADATIONAL
COOLING TO CREATE FROST IN SOME LOCATIONS...AND HARD FREEZE IN THE
INTERIOR VALLEYS. WITH TEMPERATURES ARE AT OR NEAR FREEZING OVER
THE CENTRAL COAST AND SANTA YNEZ VALLEY...A FROST ADVISORY WAS
ADDED AS THERE IS STILL SEVERAL HOURS OF RADIATIVE COOLING THAT
WILL TAKE PLACE. FREEZE WARNINGS ARE WORKING OUT WELL WITH THE
LOW TEMPERATURES THUS FAR AT CUYAMA NEAR 30 DEGREES...AND
TEMPERATURE IN THE MID 20S TO MID 30S IN THE SAN LUIS OBISPO
COUNTY VALLEYS.

A COOL PATTERN SHOULD PERSIST THROUGHOUT THE WEEKEND AND THE
PACKAGE WAS TWEAKED DOWN FOR THE COMING DAYS AS COLD AIR MASS
SETTLES INTO SOUTHWEST CALIFORNIA. MOST LOCATIONS WILL BE ABOUT 3
TO 6 DEGREES BELOW NORMAL FOR DAYTIME HIGH THROUGH EARLY NEXT
WEEK. OVERNIGHT LOWS WILL QUITE CHILLY...WITH POSSIBLE FURTHER
ISSUANCES OF FROST/FREEZE PRODUCTS THROUGH THE WEEKEND.

THERMAL SUPPORT FOR THE WINDS WILL WANE SOME ON SUNDAY
MORNING...BUT NAM-WRF SOLUTIONS...AND TO A DEGREE GFS AND ECMWF
SOLUTIONS ARE STARTING TO STRENGTHEN ANOTHER RESURGENCE OF THE
SANTA ANA WINDS BETWEEN MONDAY AND TUESDAY. NAM-WRF SOLUTION SETUP
A DECENT 850 MB THETA-E RIDGE OVER THE COASTAL WATERS...WITH A
COLD POOL OF AIR SLOSHING DOWN THE OWENS VALLEY AND ACROSS THE
MOJAVE DESERT ON MONDAY. NAM-WRF 850 MB THERMAL GRADIENTS ACROSS
THE SAN GABRIEL MOUNTAINS APPROACH 10 DEGREES CELSIUS...WITH 850
MB WINDS SOLIDLY BETWEEN 50 AND 65 KNOTS OVER THE LOS ANGELES
COUNTY MOUNTAINS. 950 MB WINDS AROUND 50 KNOTS OCCUR OVER
SOUTHERN VENTURA COUNTY ON MONDAY WHEN THE COLD AIR ARRIVES...AND
STRENGTHEN TO 55 KNOTS BETWEEN MONDAY NIGHT AND TUESDAY. THERE IS
A POSSIBILITY THAT THE STRONGEST WINDS OF THE FORECAST
PERIOD...AND SINCE WEDNESDAY NIGHTS EVENT...WILL OCCUR DURING THE
TIME PERIOD BETWEEN MONDAY AND TUESDAY.

.LONG TERM (WEDNESDAY-FRIDAY)...

LOW TEMPERATURES ACROSS THE AREAS MAY BE ABOUT 5 DEGREES LOWER
THAN THE CURRENT PACKAGE INDICATES BETWEEN WEDNESDAY AND THURSDAY
AS STILL DRIER AIR MASS SETTLES INTO THE AREA. WEAKENING OFFSHORE
FLOW WILL ALLOW FOR DAYTIME TEMPERATURES TO WARM...BUT COLD
OVERNIGHT LOWS WILL CONTINUE.

&&

.AVIATION...03/1122Z.

CLEAR SKIES THRU THE PD. MAIN ISSUE WILL BE
WINDS...WITH GUSTY NE WINDS IN THE MTNS OF L.A. AND VTU COUNTIES
SPREADING INTO THE VALLEYS AND TO PORTIONS OF THE COASTAL PLAIN.
EXPECT UDDFS NEAR THE MTNS...AND SOME LOW LVL WIND SHEAR WILL
LIKELY AFFECT AT LEAST KBUR AND KVNY THIS MORNING. WINDS WILL
DIMINISH LATE THIS AFTERNOON AND EVENING BUT WILL LIKELY RETURN
AGAIN LATE TONIGHT/SUNDAY MORNING.

KLAX...HIGH CONFIDENCE IN 12Z CAVU TAF. THERE IS A 20 PERCENT
CHANCE THAT NE WINDS COULD REACH 10 KNOTS BETWEEN 13Z AND 18Z.

KBUR...HIGH CONFIDENCE IN 12Z CAVU TAF. THERE IS A 20 PERCENT
CHANCE LLWS WILL LINGER AT THE AIRPORT AS LATE AS 20Z.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING (SEE LAXNPWLOX).
RED FLAG WARNING (SEE LAXRFWLOX).
FREEZE WARNING (SEE LAXNPWLOX).
FREEZE WATCH (SEE LAXNPWLOX).
WIND ADVISORY (SEE LAXNPWLOX).
FROST ADVISORY (SEE LAXNPWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).

&&

PUBLIC...HALL
AVIATION...DB
SYNOPSIS...HALL

WWW.WEATHER.GOV/LOSANGELES

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