Area Forecast Discussion
Issued by NWS Los Angeles, CA

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FXUS66 KLOX 281300
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
344 AM PST SAT FEB 28 2015

.SYNOPSIS...
A COLD LOW PRESSURE SYSTEM WILL BRING SHOWERS...POSSIBLE
THUNDERSTORMS AND MOUNTAIN SNOW TO THE AREA THIS WEEKEND. AFTER
A BRIEF BREAK...ANOTHER COLD SYSTEM WILL BRING SIMILAR WEATHER
LATE MONDAY MORNING THROUGH EARLY TUESDAY. DRY WEATHER IS EXPECTED
LATE TUESDAY THROUGH FRIDAY. THERE WILL BE A WARMING TREND...WITH
DAYTIME TEMPERATURES LIKELY ABOVE NORMAL BY THURSDAY.


&&

.SHORT TERM (TODAY-MON)...SKIES WERE GENERALLY MOSTLY CLOUDY ACROSS
THE REGION EARLY THIS MORNING...EXCEPT STILL MOSTLY CLEAR TO
PARTLY CLOUDY ACROSS COASTAL SECTIONS SOUTH OF POINT CONCEPTION.
SOME LIGHT SHOWERS HAVE DEVELOPED IN THE SAN GABRIEL MOUNTAINS AND
IN THE SAN GABRIEL VALLEY...PARTICULARLY IN THE FOOTHILLS. SCATTERED
SHOWERS CONTINUED TO MOVE SOUTHEASTWARD ACROSS THE COASTAL WATERS
THIS MORNING. WATER VAPOR IMAGERY SHOWED THE CENTER OF A FAIRLY
STRONG AND VERY COLD UPPER LEVEL LOW OVER EXTREME NORTHERN CA...WITH
A POTENT VORT ON ITS BACKSIDE DROPPING SOUTHWARD OFF THE COAST.

THIS UPPER LOW IS FORECAST TO DROP SOUTHWARD TODAY...WITH THE VORT
HELPING TO PULL THE UPPER CENTER SLIGHTLY OFF THE COAST TO A
POSITION JUST WEST OF MONTEREY BY LATE THIS AFTERNOON. AS THIS
HAPPENS...FLOW THROUGHOUT THE ATMOSPHERE ACROSS SOUTHWESTERN CA
SHOULD BACK FROM NWLY TO WSWLY. SHOWER ACTIVITY THAT WAS MOVING
PARALLEL TO THE COAST IN THE NWLY FLOW EARLY THIS MORNING SHOULD
BEGIN TO MOVE ONSHORE THIS AFTERNOON...ESPECIALLY IN AREAS N OF PT
CONCEPTION. INCREASINGLY MOIST CYCLONIC FLOW AND SOME EXTRA LIFT
SHOULD CAUSE SHOWER ACTIVITY TO BECOME MORE WIDESPREAD S OF PT
CONCEPTION THIS AFTERNOON...ESPECIALLY ACROSS EASTERN L.A. COUNTY.
VERY COLD AIR ALOFT WILL CAUSE INCREASING INSTABILITY...WHICH
SHOULD BRING AT LEAST A SLIGHT CHANCE OF THUNDERSTORMS TO SLO AND
SBA COUNTIES THIS AFTERNOON.

THE UPPER LOW WILL SLOWLY DROP SWD TO NEAR POINT CONCEPTION LATE
TONIGHT...MOVE VERY LITTLE ON SUNDAY...THEN PUSH SLOWLY INTO
LOS ANGELES COUNTY SUNDAY NIGHT. THIS WILL MAINTAIN A MOIST AND
UNSTABLE AIRMASS ACROSS THE REGION...SO EXPECT QUITE A BIT OF SHOWER
ACTIVITY OVERNIGHT THROUGH SUNDAY NIGHT...WITH A SLIGHT CHANCE OF
TSTMS. THE TEMPERATURE PROFILE THROUGH THE ATMOSPHERE WILL BE
FAVORABLE FOR SOME SMALL HAIL...AND INDEED...THIS HAS BEEN REPORTED
ACROSS NRN CA. ANY THUNDERSTORM THIS AFTERNOON THROUGH SUNDAY
EVENING WILL HAVE THE CAPABILITY OF PRODUCING SMALL HAIL AND HEAVY
DOWNPOURS. WHILE SHOWERS MAY OCCUR ANYWHERE AT ANY TIME...IT APPEARS
THAT THE BEST CHANCES OF ORGANIZED SHOWER ACTIVITY WILL BE TONIGHT
ACROSS L.A. COUNTY AND EASTERN VTU COUNTY AS SOME LOW LEVEL SWLY
FLOW DEVELOPS...AND SUNDAY AFTERNOON AND EVENING AS THE UPPER LOW
MOVES OVERHEAD. DUE TO THE SHOWERY NATURE OF THE PRECIPITATION...
RAINFALL TOTALS THROUGH SUNDAY NIGHT WILL BE HIGHLY VARIABLE...BUT
IN GENERAL...EXPECT TOTALS OF ONE QUARTER TO ONE HALF INCH...
EXCEPT ONE HALF INCH TO ONE INCH ACROSS THE MOUNTAINS...THE SAN
GABRIEL VALLEY...AND POSSIBLY PORTIONS OF THE REMAINDER OF THE L.A.
COUNTY VALLEYS AND THE VALLEYS OF ERN VTU COUNTY. LOCAL TOTALS UP TO
2 INCHES ARE POSSIBLE IN THE SAN GABRIEL MOUNTAINS AND FOOTHILLS.

SNOW WILL BE AN ISSUE FOR TRAVELERS THIS WEEKEND. SNOW LEVELS ARE
EXPECTED TO LOWER TO 5000 FEET LATE TODAY...THEN TO BETWEEN 3500 AND
4000 FEET LATE TONIGHT OR EARLY SUNDAY...THEN LINGER AT THOSE LEVELS
INTO SUNDAY NIGHT. SNOW MAY WELL AFFECT TRAVEL ACROSS HIGHER
PORTIONS OF INTERSTATE 5...HIGHWAY 14 AND HIGHWAY 33...ESPECIALLY
LATE TONIGHT THROUGH EARLY MONDAY. HAVE EXPANDED WINTER WEATHER
ADVISORIES TO INCLUDE THE MOUNTAINS OF SANTA BARBARA COUNTY. ON
AVERAGE...EXPECT A TOTAL OF 4 TO 8 INCHES OF SNOW BETWEEN 5000 AND
6500 FEET...WITH TOTALS OF 8 TO 12 INCHES ABOVE 6500 FEET...AND 2 TO
4 INCHES BETWEEN 4000 AND 5000 FEET. THERE COULD BE LOCAL TOTALS AS
HIGH AS 18 INCHES ACROSS PORTIONS OF THE SAN GABRIEL MOUNTAINS...OR
HIGHER ELEVATIONS IN VTU COUNTY. WAS STRONGLY CONSIDERING UPGRADING
TO A WINTER STORM WARNING...BUT HAVE DECIDED AGAINST IT...SINCE THE
SNOW ACCUMULATIONS MAY NOT MEET THE REQUIRED TOTALS IN ANY 12 OR 24
HOUR PERIOD. LATER SHIFTS MAY WELL HAVE TO UPGRADE DEPENDING UPON
SHOWER DEVELOPMENT.

SHOWERS WILL DECREASE ACROSS THE REGION SUNDAY NIGHT...AND MAY END
JUST ABOUT EVERYWHERE. HOWEVER...ANOTHER COLD UPPER LOW DROPPING
RAPIDLY SOUTHWARD WILL CAUSE SHOWERS TO BECOME LIKELY AGAIN MONDAY
AFTERNOON...WITH SHOWERS CONTINUING MONDAY NIGHT. THAT SYSTEM WILL
ALSO HAVE LOW SNOW LEVELS...AND PROBABLY ALSO A SLIGHT CHANCE OF
TSTMS. THAT SYSTEM WILL MOVE A BIT FASTER...BUT MAY ALSO TRACK A BIT
FARTHER OFF THE COAST...SO IT MAY PICK UP MORE MOISTURE. SHOWERS
SHOULD WIND DOWN IN MOST AREAS LATE MON NIGHT. MAX TEMPERATURES WILL
BE WELL BELOW NORMAL THROUGH MONDAY.

.LONG TERM (TUE-FRI)...THERE COULD BE A FEW LINGERING SHOWERS
TUE...BUT THAT IS LOOKING LESS AND LESS LIKELY. HEIGHTS WILL REBOUND
TUE AFTERNOON...AND WITH SOME SUNSHINE...EXPECT AT LEAST A BIT OR
WARMING. THE 06Z GFS NOW SHOWS A WEAK IMPULSE DROPPING SWD INTO THE
REGION ON WED...AND THAT WAS NOT ON THE PREVIOUS RUN. NO SHOWER
EXPECTED...BUT IT COULD KEEP MAX TEMPS ON THE COOL SIDE. AN UPPER
RIDGE AND HIGHER HEIGHTS WILL BRING WARMER WEATHER THU AND
FRI...WITH DAYTIME TEMPS LIKELY ABOVE NORMAL.


&&

.AVIATION...28/1135Z...

AT 0940Z...THE INVERSION AT KLAX WAS BASED AT 4300 FEET. THE TOP OF
THE INVERSION WAS AT 6300 FEET WITH A TEMPERATURE OF 5 DEGREES
CELSIUS.

OVERALL...LOW CONFIDENCE IN 12Z TAF PACKAGE. INCREASING COLD AND
UNSTABLE AIR MASS WILL GENERATE SHOWERS THROUGHOUT THE TAF PERIOD.
ADDITIONALLY...THERE WILL BE THE POSSIBILITY OF TSTMS FROM THIS
AFTERNOON THROUGH TONIGHT. CIGS WILL VARY RANDOMLY...GENERALLY
BETWEEN MVFR AND VFR LEVELS.

KLAX...LOW CONFIDENCE IN 12Z TAF. CIGS WILL BOUNCE BETWEEN MVFR AND
VFR LEVELS THROUGH THIS AFTERNOON. SHOWERS WILL LIKELY BEGIN LATE
THIS AFTERNOON/EARLY THIS EVENING (ALTHOUGH CONFIDENCE IN EXACT
START TIME IS VERY LOW). CHANCES OF TSTMS AT THE AIRFIELD TONIGHT
WILL BE 10-15%.

KBUR...LOW CONFIDENCE IN 12Z TAF. CIGS WILL BOUNCE BETWEEN MVFR AND
VFR LEVELS THROUGH THIS AFTERNOON. SHOWERS WILL LIKELY BEGIN LATE
THIS AFTERNOON/EARLY THIS EVENING (ALTHOUGH CONFIDENCE IN EXACT
START TIME IS VERY LOW). CHANCES OF TSTMS AT THE AIRFIELD TONIGHT
WILL BE 10-15%.

&&

.MARINE...28/330 AM...

FOR THE OUTER WATERS...HIGH CONFIDENCE IN SMALL CRAFT ADVISORY LEVEL
NORTHWEST WINDS CONTINUING THROUGH THIS MORNING...BEFORE DIMINISHING
BELOW ADVISORY LEVELS THIS AFTERNOON. HIGH CONFIDENCE IN WINDS
REMAINING BELOW SMALL CRAFT ADVISORY LEVELS SUNDAY THROUGH
MONDAY...WITH A CHANCE OF WINDS INCREASING ON TUESDAY.

FOR THE INNER WATERS...HIGH CONFIDENCE IN SMALL CRAFT ADVISORY LEVEL
WEST TO NORTHWEST WINDS CONTINUING THROUGH THIS MORNING...BEFORE
DIMINISHING BELOW ADVISORY LEVELS THIS AFTERNOON. HIGH CONFIDENCE IN
WINDS REMAINING BELOW SMALL CRAFT ADVISORY LEVEL SUNDAY THROUGH
EARLY NEXT WEEK.

A COLD AND UNSTABLE AIR MASS WILL MOVE OVER THE COASTAL WATERS TODAY
AND CONTINUE THROUGH MONDAY. THIS WILL RESULT IN SHOWERS ALONG WITH
THE SLIGHT CHANCE OF THUNDERSTORMS THROUGH THE PERIOD. ANY
THUNDERSTORMS THAT DEVELOP WILL LIKELY PRODUCE GUSTY WINDS...ROUGH
AND CHOPPY SEAS AS WELL AS SMALL HAIL. ADDITIONALLY...THERE WILL BE
THE POSSIBILITY OF AN ISOLATED WATERSPOUT.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY (SEE LAXWSWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
HIGH RIP CURRENT RISK (SEE LAXSRFLOX).
MARINE WEATHER STATEMENT (SEE LAXMWSLOX).

&&

$$

PUBLIC...DB
AVIATION/MARINE...RAT
SYNOPSIS...DB

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