Wind Advisory 139, NWS Los Angeles, CA

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
150 PM PST THU DEC 6 2007

.SHORT TERM (TODAY-SUN)...COLD FRONT RAPIDLY APPROACHING SO CAL THIS
AFTERNOON. EASTWARD SPEED ESTIMATED AT ABOUT 35-40 KT. THE GFS HAS
BEEN CONSISTENTLY SHOWING THE FRONT MOVING QUICKLY THROUGH THE AREA
AND THIS LIKELY WILL BE THE CASE BASED ON WHAT WERE SEEING ON
SATELLITE THIS AFTERNOON. THERE IS STILL A SMALL CHANCE THAT IT
COULD SLOW DOWN OR EVEN STALL ONCE IT ROUNDS PT CONCEPTION BUT THIS
IS UNLIKELY. 18Z NAM STILL SHOWING STRONG SOUTHERLY WINDS DEVELOPING
AS THE FRONT APPROACHES, PARTICULARLY IN THE MOUNTAINS, AND WILL
ISSUE A WIND ADVISORY FOR THESE AREAS TONIGHT AND FRIDAY. THE
SOUTHERLY FLOW WILL PUMP UP SNOW LEVELS CONSIDERABLY TONIGHT AND
LATEST MODELS ARE SHOWING THE FREEZING LEVEL ABOVE 700 MB THROUGH
FRIDAY MORNING. SO ANY SNOW THAT DOES FALL TONIGHT WILL BE ON THE
VERY HIGHEST PEAKS WITH VERY LITTLE IN THE WAY OF ACCUMULATION.

PEAK RAIN RATES FROM THIS SYSTEM COULD STILL EXCEED BURN AREA
THRESHOLDS FOR MUD AND DEBRIS FLOWS SO THE FLASH FLOOD WATCH LOOKS
GOOD. THE HEAVIEST PERIOD OF RAIN SHOULD BE VERY BRIEF, PERHAPS JUST
A FEW HOURS BEFORE RAIN TURNS SHOWERY IN NATURE BEHIND THE FRONT.
THIS WILL SIGNIFICANTLY LIMIT RAINFALL TOTALS, BUT CURRENT
PROJECTIONS OF A HALF TO ONE INCH MOST AREAS STILL LOOKS GOOD.
ISOLATED AMOUNTS UP TO 3 INCHES ARE POSSIBLE OVER THE SOUTH FACING
MOUNTAINS AND FOOTHILLS.

COLD AIR BEHIND THE FRONT WILL ARRIVE ON FRIDAY AND DROP SNOW LEVELS
CONSIDERABLY. HOWEVER, MOST OF THE MOISTURE WILL HAVE MOVED THROUGH
BY THEN SO SHOWERS AND SNOW AMOUNTS WILL BE SCATTERED IN NATURE.
THERE IS STILL THE POTENTIAL FOR A FOOT OF SNOW AT THE HIGHEST
ELEVATIONS WITH THIS EVENT BUT MUCH LOWER AMOUNTS ELSEWHERE.

LINGERING SHOWER ACTIVITY FRIDAY AFTERNOON THROUGH SATURDAY APPEARS
TO BE MINIMAL AND MAINLY CONFINED TO LA COUNTY. HOWEVER, CANT RULE
OUT A STRAY SHOWER ANYWHERE AS AIRMASS WILL STILL BE SLIGHTLY
UNSTABLE.

WILL HAVE TO KEEP A CLOSE EYE ON WRAP AROUND MOISTURE SATURDAY NIGHT
AS ANOTHER IMPULSE ROTATES AROUND THE TROF INTO LA COUNTY. THIS
COULD BE A SCENARIO WHERE THE EASTERN SAN GABRIEL MOUNTAINS GETS HIT
PRETTY HARD WITH NORTH SLOPE SNOW AND POSSIBLY EVEN SOME SNOW DOWN
TO THE ANTELOPE VALLEY FLOOR, BUT THIS IS A SMALL SCALE EVENT AND
VERY DIFFICULT TO PREDICT THIS FAR IN ADVANCE. FOR NOW WILL LEAVE IN
HIGHER PRECIP CHANCES OVER EASTERN LA COUNTY SAT NIGHT AND WILL SEE
HOW THE STORM EVOLVES BEFORE COMMITTING TO ANYTHING TOO SIGNIFICANT.

OVERNIGHT LOWS WILL PLUMMET FRIDAY NIGHT BEHIND THE FRONT WITH TEMPS
DROPPING INTO THE 30S IN WIND PROTECTED VALLEYS AND TEENS AND 20S IN
WIND PROTECTED MOUNTAIN LOCATIONS. COLD NIGHTTIME TEMPS WILL
CONTINUE THROUGH THE WEEKEND AS THE TROF CONTINUES TO USHER IN COLD
AIR FROM THE NORTHEAST. HIGHS WILL REMAIN SEVERAL DEGREES BELOW
NORMAL.

.LONG TERM (MON-THU)...MODELS HAVE BACKED OFF THE RIDGING FOR NEXT
WEEK, MEANING THE WARMING TREND IS NOW ON HOLD. HOWEVER, DRY
CONDITIONS ARE STILL EXPECTED. WITH MORE SUN AND A WEAK OFFSHORE
FLOW THERE WILL BE SOME REBOUND IN TEMPS, BUT NOT MUCH. OFFSHORE
GRADIENTS DO INCREASE WED AND THU MORNING AND WILL HAVE TO WATCH FOR
POSSIBLE GUSTY NORTHEAST WINDS, HOWEVER THE AIRMASS IS COLD SO THIS
WILL OFFSET ANY EFFECTS FROM THE OFFSHORE FLOW.

&&

.AVIATION...06/2120Z

INCREASING CLOUDS AND PRECIPITATION ARE EXPECTED TONIGHT. LOW CLOUDS
HAVE PERSISTED SOUTH OF POINT CONCEPTION IN THE VICINITY OF THE
CATALINA EDDY AND WILL LIKELY CONTINUE THROUGH THE NIGHT IN ADVANCE
OF AN APPROACHING COLD FRONT. NORTH OF POINT CONCEPTION...CLOUDS
WERE SLOWLY INCREASING AND LOWERING. MVFR TO IFR CONDITIONS ARE
EXPECTED ACROSS THE ENTIRE DISTRICT LATER TONIGHT INTO FRIDAY
MORNING ASSOCIATED WITH THE COLD FRONT AND ASSOCIATED PRECIPITATION.
IN ADDITION...EAST TO SOUTHEAST WINDS WILL BECOME WIDESPREAD AND
RATHER GUSTY OVERNIGHT AHEAD OF THE FRONT. STRONG WEST WINDS ARE
EXPECTED ON FRIDAY BEHIND THE FRONT.

KLAX AND KBUR...BKN TO OVC CONDITIONS ARE EXPECTED FROM NOW THROUGH
FRIDAY MORNING AS CLOUDS INCREASE DUE TO AN APPROACHING FRONT.
DURING THE OVERNIGHT HOURS...EAST WINDS WILL DEVELOP IN EXCESS OF 10
KTS AND QUITE POSSIBLY IN EXCESS OF 20 KTS. MVFR TO IFR CONDITIONS
ARE EXPECTED IN LOW CLOUDS AND PRECIPITATION UNTIL THE FRONT PASSES
THROUGH AROUND 16-17Z FRIDAY. AFTER THE FRONT...EXPECT STRONG GUSTY
WEST WINDS AND CLEARING SKIES.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH (SEE LAXFFALOX).
SMALL CRAFT ADVISORY (SEE LAXCWFLOX).
HIGH RIP CURRENT RISK (SEE LAXSRFLOX).

&&

PUBLIC...WOFFORD
AVIATION...SWEET

WWW.WEATHER.GOV/LOSANGELES

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