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[Printable]
231
FXUS66 KLOX 201833
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1130 AM PDT WED AUG 20 2014

...NEW AVIATION DISCUSSION...

.SYNOPSIS...

A SLIGHT CHANCE OF THUNDERSTORMS TODAY IN LOS ANGELES COUNTY AND IN
THE VENTURA COUNTY MOUNTAINS. A SLIGHT CHANCE OF THUNDERSTORMS
TOMORROW IN THE LOS ANGELES AND VENTURA COUNTY MOUNTAINS AND THE
ANTELOPE VALLEY. AFTERNOON HIGHS BELOW NORMAL THROUGH THE END OF THE
WEEK WITH LOW CLOUDS ALONG THE COAST AND IN ADJACENT VALLEYS.
CLEARER SKIES AND WARMER TEMPERATURES ARE ON TAP FOR THE WEEKEND.

&&

.SHORT TERM (TODAY-FRI)...
*** MID-MORNING DISCUSSION UPDATE ***
BIG QUESTION TODAY WILL BE WHETHER AND WHEN THUNDERSTORMS SLIDE INTO
LOS ANGELES COUNTY TODAY AND IF ANY DEVELOPMENT MAKES IT INTO THE
VENTURA COUNTY MOUNTAINS AS WELL.  THE PRIMARY RAIN BAND CONTINUES
TO SLIDE SOUTHEASTWARD ACROSS SAN DIEGO... RIVERSIDE... AND SAN
BERNARDINO COUNTIES THIS MORNING.  HOWEVER AS THE CENTER OF THE LOW
DROPS SOUTHWARD INDICATES CONTINUE TO SHOW A LIKELIHOOD OF THE
THUNDERSTORM BAND WRAPPING AROUND INTO LOS ANGELES COUNTY THIS
AFTERNOON.  WITH GOOD INSTABILITY STRINGING ACROSS THE REGION INTO
THE MOUNTAINS OF SAN LUIS OBISPO COUNTY IT APPEARS THAT DEVELOPMENT
WILL NOT BE A PROBLEM BUT THE BEST MOISTURE APPEARS TO STAY TO THE
SOUTHEAST SO THIS COULD BE A LIMITING FACTOR ESPECIALLY FOR ANYTHING
WEST OF THE SAN GABRIEL RANGE.  LOOKS BETTER TOMORROW... BUT THEN
THE LOW MAY BE OUT OF POSITION.

NOT ANTICIPATING ANY NOTABLE CHANGES TO THE FORECAST PACKAGE AT THIS
TIME OTHER THAN POSSIBLE TWEAKING FOR THUNDERSTORM DEVELOPMENT TODAY
AND TOMORROW.

*** EARLY MORNING DISCUSSION ***
WHAT A DIFFERENCE 60 MILES MAKES. ALL OF L.A. COUNTIES COASTS AND
VLYS AS WELL AS THE COASTAL SLOPES ARE COVERED WITH LOW CLOUDS. 60
MILES SOUTH AT THE NW TIP OF SAN DIEGO COUNTY A PERSISTENT LINE OF
TSTMS IS RUMBLING ON. THE MARINE LAYER IS 3000 FEET DEEP BUT THE
CLOUD LAYER IS PRETTY THIN AND EXPECT DECENT CLEARING TODAY...EXCEPT
FOR THE CENTRAL COAST WHERE THE BEACHES WILL SEE SLOW TO NO
CLEARING. THE COASTAL/VALLEY FORECAST SAYS MOSTLY SUNNY THIS
AFTERNOON BUT THIS DEEP A MARINE LAYER MIGHT PRODUCE SOME AFTERNOON
STRATA CU. TSTMS ARE THE REAL STORY OF THE DAY. ALL BROUGHT TO US
COURTESY OF 576 DM UP LOW JUST TO THE WEST OF CATALINA ISLAND. A
VORT MAX WHIPPING AROUND THE BASE OF THE LOW IS PROVIDING THE FOCUS
FOR THE SAN DIEGO COUNTY TSTMS. THERE IS A SLIGHT CHC THAT A TSTM
COULD FORM OVER L.A. COUNTY OR THE ADJACENT WATERS EARLY THIS
MORNING BUT FOR THE MOST PART THE CONVECTION WILL STAY TO THE SOUTH.
THINGS CHANGE LATER THIS MORNING HOWEVER. THE UPPER LOW DROP A
LITTLE MORE SOUTHWARD AND THE FLOW PATTERN SHIFTS FROM THE SW TO THE
SSW. THIS WILL PUSH THE MOISTURE AND LIFT FORM THE UPPER LOW
NORTHWARD INTO ERN LA COUNTY. BY EARLY AFTERNOON THE LOW HAS SETTLED
FURTHER SOUTH AND THE FLOW PATTERN GOES FROM NEAR SAN CLEMENTE TO
PASADENA TO LANCASTER. THIS FLOW PATTERN LOOKS PRETTY CONDUCIVE FOR
CONVECTION AND SHOULD LAST INTO THE EVENING. THE LA COASTS AND VLY
WILL HAVE A SLIGHT CHC OF TSTMS WHILE THE MTNS AND DESERTS (AS WELL
AS THE VTA COUNTY MTNS) WILL HAVE A CHC. THERE IS NOT MUCH MOISTURE
TO WORK WITH AND ANY STORMS THAT DO FORM WILL MOVE AT A PRETTY GOOD
CLIP SO THE THREAT OF FLASH FLOODING IS FAIRLY SMALL. 578 HGTS...
THE DEEP MARINE LAYER AND GOOD ONSHORE FLOW WILL ALL CONTRIBUTE TO A
MUCH COOLER THAN NORMAL DAY.

UNLESS SOME REALLY HUGE TSTMS DEVELOP TODAY WITH OUTFLOW POWERFUL
ENOUGH TO DISRUPT THE MARINE INVERSION (UNLIKELY) THERE WILL BE
ANOTHER ROUND OF LOW CLOUDS COVERING THE COASTS AND VLYS TONIGHT.
EXPECT GOOD CLEARING THURSDAY AND ALMOST ALL AREAS SHOULD BE SUNNY
BY NOON. THERE IS JUST ENOUGH WRAP AROUND MOISTURE ASSOC WITH THE
EXITING UPPER LOW TO ALLOW FOR A SLIGHT CHC OF AFTERNOON TSTMS OVER
THE LA/VTA MTNS. MAX TEMPS WILL RISE SOME DUE TO HIGHER HGTS AND
WEAKER ONSHORE FLOW BUT ALL TEMPS WILL STILL BE BLO NORMAL.

THE UPPER LOW WILL OPEN UP AND MOVE EASTWARD INTO ARIZONA BY
THURSDAY NIGHT AND WILL NO LONGER INFLUENCE OUR WEATHER. HGTS RISE
AND THE ONSHORE FLOW DECREASES THE MARINE LAYER WILL SHRINK. IT WILL
MOST LIKELY SHRINK OUT OF THE VLYS BUT THERE IS A 30 OR 40 PERCENT
CHANCE THAT SOME VLYS WILL HAVE ONE MORE NIGHT OF LOW CLOUDS. MORE
WARMING WILL BRING MAX TEMPS BACK CLOSE TO NORMAL.

.LONG TERM (SAT-TUE)...
EXTENDED MDLS HAVE BEEN TERRIBLE ALL SUMMER AND TONIGHTS RUN ARE
EQUALLY TROUBLED. YESTERDAYS BUILDING HIGH PRESSURE WAS DIFFERENT
FROM MONDAYS CULL AREA FCST AND TODAYS FORECAST CALLS FOR 4 DAYS OF
A LONG WAVE TROF. DID NOT MAKE A BUNCH OF CHANGED TO THE LONG RANGE
FORECAST. LOWERED MAX TEMPS A FEW DEGREES SINCE THE THE RIDGE IS NO
LONGER IN THE PICTURE...BUT DID NOT MESS WITH THE MARINE LAYER
CLOUDS WHICH IF THIS SCENARIO COMES TRUE WILL BE DEEPER THAN FCST
AND WILL AFFECT THE VLYS.

&&

.AVIATION...20/1800Z.
A COOL DISTURBANCE ALOFT HAS MANAGED TO KEEP A LINE OF THUNDERSTORMS
GOING JUST SOUTH OF OUR FORECAST AREA...BUT SO FAR THERE HAS BEEN NO
EFFECT ON OUR FORECAST DISTRICT. THERE IS A CONTINUED CHANCE OF
THUNDERSTORM ACTIVITY IN THE DESERT TAFS AND IT IS MENTIONED IN THE
KPMD AND KWJF TAFS. OTHERWISE...EXPECTING A RETURN OF THE MARINE
CLOUDS TONIGHT INTO THURSDAY MORNING WITH A MARINE LAYER DEPTH OF
AROUND 3000 FEET SOUTH WITH SOME SHALLOWING POSSIBLE NORTH OF POINT
CONCEPTION AND MVFR TO VFR CEILINGS. THERE IS A SLIGHT CHANCE THAT
THE MARINE CLOUDS WILL NOT DEVELOP AT EXPECTED.

KLAX AND KBUR...GOOD CONFIDENCE IN THE 18Z TAFS. THERE IS A 20
PERCENT CHANCE OF VFR CONDITIONS THROUGH THURSDAY.

&&

.MARINE...20/900 AM...

NO SIGNIFICANT WIND ISSUES ANTICIPATED ACROSS THE COASTAL WATERS FOR
THE NEXT SEVERAL DAYS.

THERE IS THE POSSIBILITY OF SOME ISOLATED THUNDERSTORMS ACROSS THE
SOUTHERN WATERS THROUGH THIS EVENING...WITH GUSTY WINDS AND CHOPPY
SEAS LIKELY WITH ANY THUNDERSTORMS.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
MARINE WEATHER STATEMENT (SEE LAXMWSLOX).

&&

$$

PUBLIC...RORKE/KJ
AVIATION...SWEET
MARINE...SWEET
SYNOPSIS...SETO

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