000
FXUS66 KLOX 070527
AFDLOX
SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1030 PM PDT MON OCT 6 2008
...UPDATED AVIATION DISCUSSION...
.UPDATE...WEAK OFFSHORE FLOW PATTERN KEEPING THE MARINE LAYER
ABSENT FROM THE AREA THIS EVENING. 00Z KNKX SOUNDING INDICATES
WARMING IN THE LOWEST LEVELS OF THE ATMOSPHERE WITH 950 MB
TEMPERATURES WARMING BY TEN DEGREES CELSIUS OVER THE LAST 24
HOURS...WHILE CURRENT WATER VAPOR IMAGERY ILLUSTRATES THE UPPER-
LEVEL RIDGE OF HIGH PRESSURE BUILDING OVER THE AREA.
A WARMER DAY SEEMS TO BE DEVELOPING FOR TUESDAY AS THE RIDGE
CONTINUES TO BUILD OVER THE AREA AND SURFACE GRADIENTS CONTINUE
TO TREND OFFSHORE. MODELS SEEM TO BE THROWING IN SOME UNCERTAINTY
THOUGH. NAM-WRF MODEL INITIALIZATION SEEMS ABOUT TWO TO THREE
DEGREES CELSIUS TOO WARM AT 950 MB BASED ON UPPER-AIR DATA FROM
KNKX AND KOAK SITES. 18Z GFS 950 MB PATTERN SEEMS TO BE DOING A
BETTER JOB...WITH ONLY SLIGHT DIFFERENCES AT 950 MB. OVERALL...THE
CURRENT PACKAGE APPEARS TO BE REASONABLE FOR WARMING FOR TUESDAY
BASED ON CURRENT TRENDS...AND BEST APPROACH IS TO WAIT FOR
EVENING GFS SOLUTION BEFORE MAKING ANY CHANGES TO THE PACKAGE.
RIDGE STARTS TO WEAKEN FOR MIDWEEK AND INTO THE LATTER PART OF THE
WEEK AS STRONG WESTERLY FLOW OVER THE PACIFIC NORTHWEST WEAKENS
THE RIDGE OF HIGH PRESSURE...AND TROUGH DIGS SOUTH ALONG THE
PACIFIC NORTHWEST COAST. GOOD AGREEMENT EXISTS BETWEEN THE MODELS
INDICATING THE RIDGE WEAKENING SOME...SURFACE GRADIENTS TRENDING
ONSHORE...AND 950 MB COOLING FOR WEDNESDAY AND THURSDAY. THIS
COULD BE AN ALTERING POINT FROM THE CURRENT PACKAGE AS PACKAGE HAS
WEDNESDAY BEING AS WARM AS TUESDAY AFTERNOON...BUT MODEL SUGGEST
OTHERWISE. NEXT SHIFT WILL BE BRIEFED ON THIS ISSUE.
MODEL SOLUTIONS START DIVERGING AS THE TROUGH APPROACHES THE WEST
COAST. NAM-WRF...GFS...AND ECMWF SOLUTIONS ARE IN PRETTY GOOD
AGREEMENT WITH THE UPPER-LEVEL PATTERN THROUGH WEDNESDAY
NIGHT...BUT 500 MB HEIGHTS SEEM TO BE RATHER MUDDLED THROUGH LATE
WEEK. GFS ENSEMBLE SOLUTIONS OFFER LITTLE CONFIDENCE ON WHICH WAY
TO TREND. WITH NAM-WRF SOLUTIONS FOLLOWING MORE CLOSELY TO THE
ECMWF SOLUTIONS...HIGHER CONFIDENCE SHOULD BE PLACED IN THE NAM-
WRF AND ECMWF SOLUTIONS IN THE MID TO LONG TERM. LATER PACKAGES
MAY LEAN TOWARD THE ECMWF SOLUTION OF A STRONGER INSIDE-SLIDER
TROUGH MOVING THROUGH THE GREAT BASIN. THIS COULD INTRODUCE POPS
AND RAIN CHANCES INTO THE FORECAST AREA...AND POSSIBLY A MODERATE
OFFSHORE EVENT FOR THE AREA OVER THE WEEKEND. A COOLING AND MORE
MOIST TREND SHOULD BE EXPECTED FOR LATE WEEK WITH MARINE LAYER
ENHANCEMENT AHEAD OF THE TROUGH. A DRYING TREND SHOULD OCCUR OVER
THE WEEKEND...WITH A POSSIBLE WARMING TREND FOR EARLY NEXT WEEK.
&&
.PREV DISCUSSION... /ISSUED 200 PM PDT MON OCT 6 2008/
SHORT TERM (TODAY-THURSDAY)...
WITH LAX-DAG PEAKING NEAR -2 MB AND SMX-BFL NEAR -3 MB THIS
MORNING...OFFSHORE GRADS HAVE BROUGHT SOME LIGHT TO MODERATE
NORTHEAST FLOW TO THE MTNS AND FAVORED VALLEYS. WITH THIS FLOW ALSO
KEEPING THE STRATUS AT BAY WHILE A 592 DM RIDGE BUILDS IN FROM THE
SOUTHWEST...TEMPS ARE UP ACROSS THE BOARD. VLYS AND MTNS ARE
TRENDING UP ABOUT 10 DEGREES FROM YESTERDAY...WITH COASTAL SPOTS
TRENDING JUST UNDER THAT CLIP.
TEMPS LOOK TO CONTINUE THE WARM UP TUE AND WED...AS OFFSHORE GRADS
INCREASE A BIT MORE AND THE RIDGE CONTINUES TO NUDGE DEEPER INTO THE
SOUTHWEST US. IN ADDITION...MIN TEMPS WILL SEE A LITTLE BOOST AS
WELL...GIVING US A BIT OF A BREAK FROM THE FALL LIKE MORNING TEMPS
WE HAVE BEEN FEELING. EAST WINDS SHOULD REFORM EACH MORNING THROUGH
THOSE PASSES AND CANYONS...AS WELL AS A FEW MTN PEAKS...BUT SHOULD
REMAIN WELL BELOW ADVISORY STRENGTH. CENTRAL COAST WILL CONTINUE TO
BE THE TRICKIEST TO FORECAST...BEING HEAVILY DEPENDENT ON HOW MUCH
WIND SURFACES AND IF IT CONTINUES INTO THE AFTERNOON. CURRENT
FORECAST REFLECTS MIDDLE OF THE RANGE OF POSSIBLE OUTCOMES.
THINGS SHOULD BEGIN TO COOL ON THU...AS A TROUGH AMPLIFIES TO THE
NORTH AND DIGS SOUTHWARD TO OUR EAST. THIS WILL RAPIDLY TURN GRADS
ONSHORE AND DROP THICKS...RESULTING IN COOLING EVERYWHERE BUT
ESPECIALLY IN THE LA/VTU VLYS AND MTNS. DID INTRODUCE SOME DENSE
FOG TO THE THU MORNING FORECAST FOR LA/VTU COAST DUE TO NEAR
NEUTRAL MORNING GRADS AND A WEAK EDDY POSSIBLY SPINNING UP.
ALTHOUGH THIS WILL QUIET THE OFFSHORE FLOW...SOME BREEZY NW WINDS
WILL LIKELY BE FELT ALONG THE CENTRAL COAST AND SOME OF THE MTNS
AND DESERTS.
LONG TERM (FRIDAY-MONDAY)...
AS THE PREVIOUSLY MENTIONED INSIDE SLIDING TROUGH DIGS FURTHER TO
THE SOUTH AND INTO UTAH FRI NIGHT...TEMPS SHOULD CONTINUE TO COOL
FRI AND SAT...ESPECIALLY IN THE MTNS. IT COULD COOL EVEN MORE THAN
THE CURRENT FORECAST REFLECTS IF THE 12Z ECMWF SOLN MATERIALIZES...
AS IT KEEPS THE LOW FURTHER WEST ON FRI NIGHT THAN THE GFS. CURRENT
PACKAGE IS WEIGHTED MORE ON THE 12Z GFS AND THE PREVIOUS 00Z
ECMWF...BUT NUDGED A BIT IN THE 12Z ECMWF DIRECTION.
AS WITH ALL INSIDE SLIDERS...THIS WILL CONTINUE TO BE A DEVELOPING
STORY...AND THE BEST FORECAST IS THAT THE MODELS WILL CONTINUE TO
WAVER EACH RUN. THE ONE STORY THAT HAS BEEN CONSISTENT OVER THE LAST
COUPLE OF DAYS AND CONTINUES TO LOOK FAVORABLE IS THAT WE COULD BE
IN STORE FOR OUR FIRST SANTA ANA EVENT OF THE YOUNG SEASON. STARTING
SAT OR SUN AND CONTINUING INTO MON...THE COLD AIR ASSOCIATED WITH
THIS SYSTEM WILL CREATE A HEALTHY SURFACE HIGH IN THE GREAT BASIN.
ALTHOUGH THE ECMWF AND THE GFS DIFFER IN TIMING AND INTENSITY...THIS
SHOULD BE A SIGNIFICANT EVENT. THERE IS A GOOD CHANCE OF MULTIPLE
WIND ADVISORIES AND POSSIBLE WARNINGS FIRST IN THE MTNS ON SAT FOR
NORTHERLY FLOW...THEN INTO THE VLYS SUN AS THE FLOW SHIFTS
NORTHEAST. DID TEMPER THE WARMING IN THE VLYS AND COASTAL AREAS OVER
THE WEEKEND...AS THE COLD AIR ASSOCIATED WITH THE LOW MAY LINGER
AROUND AB IT LATER.
&&
.AVIATION...07/0525Z.
VFR CONDITIONS WILL LIKELY OCCUR AT MOST TERMINALS THROUGHOUT THE
PERIOD...EXCEPT FOR 20 PERCENT CHANCE OF MVFR VISIBILITIES EXPECTED
AT KSMX BETWEEN 10-13Z.
KLAX AND KBUR...VFR CONDITIONS ARE EXPECTED THROUGHOUT THE PERIOD
WITH NO WIND ISSUES.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
PUBLIC...HALL/KITTELL
AVIATION...KAPLAN
WWW.WEATHER.GOV/LOSANGELES
