FORECAST DISCUSSION

FXUS66 KLOX 182340
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
340 PM PST SAT FEB 18 2006

.SHORT TERM...
A COLD UPPER LEVEL LOW IS CURRENTLY LOCATED WEST OF SAN FRANCISCO
WITH CYCLONIC FLOW DOMINATING DOMINATING THE SOUTHWEST US...COASTAL
AND OFFSHORE WATERS. THE INSTABILITY DUE TO THE CYCLONIC FLOW AND
COLD AIR ALOFT HAS PRODUCED NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS OVER SOUTHWESTERN CALIFORNIA AND THE COASTAL WATERS.
MOST AREAS HAVE SEEN SOME SHOWER AND THUNDERSTORM ACTIVITY TODAY...
WITH THE EXCEPTION OF THE ANTELOPE VALLEY.

IN 24 HOURS...THE COLDEST POOL OF AIR ASSOCIATED WITH THE LOW SHIFTS
DIRECTLY EAST WITH THE TROUGH REMAINING ALMOST STATIONARY. THUS...
THE CYCLONIC FLOW AND THE RESULTANT PATTERN FOR SHOWERS IS EXPECTED
TO CONTINUE THROUGH MUCH OF THE NEXT 24 HOURS.

WHILE THERE IS STILL POOR DEFINITION OF A COHESIVE FRONTAL SYSTEM IN
EITHER THE SATELLITE OR RADAR DATA AT THIS TIME...THERE IS STILL A
HEAVIER BAND OF SHOWERS AND ISOLATED THUNDERSTORMS THAT IS EXPECTED
TO DEVELOP AND REVOLVE AROUND THE LOW IN THE NEXT 24 HOURS. IT IS
EXPECTED TO DEVELOP ALONG THE CENTRAL COAST LATER THIS EVENING AND
MOVE SOUTH AND EAST THOUGH THE REGION OVERNIGHT. THIS WILL RESULT IN
AN INCREASE IN THE COVERAGE AND INTENSITY OF THE SHOWERS OVERNIGHT.
THEREFORE...THE FLASH FLOOD WATCH FOR THE BURN AREAS CONTINUES...AS
DOES THE WINTER STORM WARNING FOR THE MOUNTAINS.

MODELS INDICATE THAT THIS BAND OF SHOWERS IS NOT EXPECTED TO BE AS
STRONG AS EARLIER PROJECTIONS PREDICTED. THEREFORE...SOME AREAS HAVE
BEEN DOWNGRADED TO SNOW ADVISORIES WHILE STORM TOTALS HAVE ALSO BEEN
DECREASED TO JUST ABOVE MINIMUM WARNING CRITERIA...6 TO 8 INCHES
WITH LOCAL AMOUNTS TO 10 INCHES. IN ADDITION... SHOWER INTENSITIES
ARE EXPECTED TO BE LESS THAN EARLIER EXPECTED. WHILE THE FLASH FLOOD
WATCHES WILL BE ALLOWED TO REMAIN IN EFFECT... THE POSSIBILITY FOR
MUD AND DEBRIS FLOWS IN THE BURN AREAS SEEMS TO BE DIMINISHING AS
WELL. LOOK FOR SHOWERS TO END FROM THE WEST SUNDAY AFTERNOON WITH
PARTIAL CLEARING.

SNOW LEVELS WILL NOT BE AS LOW AS EARLIER EXPECTED DUE TO THE FACT
THAT THE COLDEST AIR STAYS TO THE NORTH AND SOUTHERLY WINDS DEVELOP.
THUS...HAVE KEPT THE SNOW LEVELS AT AROUND 3500 FEET OVERNIGHT AND
HAVE DELETED THE MENTION OF SNOW IN MANY OF THE VALLEYS. HOWEVER...
STILL COULD SEE SOME FLURRIES IN THE FOOTHILLS WITH SOME VERY LIGHT
ACCUMULATIONS POSSIBLE IN COLDER AREAS BELOW 3500 FEET.

THE MAJOR TROUGH AXIS LINGERS OVER SAN FRANCISCO THROUGH MONDAY
MORNING...THEN BEGINS TO MOVE SOUTH TO LOS ANGELES BY TUESDAY
MORNING. THE DETAILS OF THIS MOVEMENT VARY FROM ONE MODEL TO THE
NEXT. HOWEVER...THERE ARE SOME COMMON FEATURES. MODELS AGREE THAT IT
WILL NOT BE AS COLD AS THE FIRST SYSTEM...BUT IT WILL ACTUALLY BRING
THE COLD AIR IT HAS FURTHER SOUTH. THIS WILL KEEP THINGS ON THE COOL
TO COLD SIDE AND BRING A LITTLE INSTABILITY TO THE FORECAST. AT THIS
TIME...THERE ARE NO SHOWERS IN THE FORECAST FOR MONDAY AND TUESDAY
DUE TO THE MOVEMENT OF THIS TROUGH...BUT THIS MAY BE OPTIMISTIC. IF
THE MOVEMENT OF THIS SYSTEM CONTINUES ON TRACK...EXPECT THAT SOME
POPS MAY NEED TO BE ADDED INTO THE FORECAST FOR MONDAY AND TUESDAY
DUE TO THE COLD AIR ALOFT AND THE DYNAMICS OF THE UPPER LOW PASSING
THROUGH THE REGION.

.LONG TERM...
THE MODEL AGREEMENT STARTS OUT BAD ON WEDNESDAY...THEN GETS BETTER
AS TIME PROGRESSES. NAM MODEL HAS A CLOSED LOW OFF THE COAST OF PT
CONCEPTION ON WEDNESDAY MORNING WITH MOIST SOUTHERLY FLOW OVER MUCH
OF THE REGION...THIS WOULD BE A RAIN FORECAST. HOWEVER...THE MEDIUM
RANGE MODELS ALL SHOW AN UPPER TROUGH EXITING THE REGION TO THE EAST
AT THE SAME TIME WITH DRY WEST TO NORTHWEST FLOW OVER THE REGION.
WOULD TEND TO AGREE WITH THE GFS AND ECMWF WITH THE EXITING UPPER
TROUGH AND THE DRYER WEST TO NORTHWEST PATTERN ALOFT OVER THE
REGION. AS THE WEEK PROGRESSES...MODEL SOLUTIONS TREND TO A
DEVELOPING PACIFIC RIDGE OVER THE REGION BY WEEKS END. THIS WOULD
MEAN IMPROVING CONDITIONS...WARMER AND DRIER AS THE WEEK PROGRESSES
WITH A NICE START TO NEXT WEEKEND. THIS IS THE SOLUTION FOLLOWED IN
THE CURRENT ZONE PACKAGE. HOWEVER...WILL NEED TO PAY STRICT
ATTENTION TO THE MONDAY TO TUESDAY SYSTEM TO SEE HOW FUTURE MODEL
RUNS HANDLE THE SITUATION. STAY TUNED FOR POSSIBLE UPDATES.

&&

.AVIATION...
SCATTERED SHOWERS WILL PERSIST THROUGH THE TAF PERIOD...CAUSING
FLUCTUATIONS IN CEILINGS AND VSBYS. HOWEVER...SHOULD NOT HAVE
ANYTHING LOWER THAN MVFR CONDS. FREEZING LEVELS WILL BE
LOW...GENERALLY BETWEEN 3000 AND 4000 FEET.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING (SEE LAXWSWLOX).
FLOOD WATCH (SEE LAXFFALOX).
SNOW ADVISORY (SEE LAXWSWLOX).

&&

PUBLIC...DANIELSON
AVIATION...MOYER