Area Forecast Discussion
Issued by NWS Los Angeles, CA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KLOX 061817 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
1045 AM PDT WED MAY 6 2015

...AVIATION DISCUSSION UPDATED...

.SYNOPSIS...

A COLD LOW PRESSURE SYSTEM WILL ARRIVE LATE TONIGHT BRINGING A
CHANCE OF SHOWERS AND THUNDERSTORMS THROUGH FRIDAY EVENING.
TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH THE WEEKEND. NEAR
NORMAL TEMPERATURES ARE LIKELY BY EARLY NEXT WEEK.

&&

.SHORT TERM (TODAY-FRIDAY)...

NO MAJOR CHANGES MADE TO TODAY`S FORECAST. VERY DEEP MARINE LAYER IN
PLACE THIS MORNING...WITH LATEST LAX AMDAR SOUNDINGS AROUND 4500
FEET. AS A RESULT...LOW CLOUDS HAVE SPREAD ALL THE INTO THE INTERIOR
VALLEYS AND HAVE EVEN SPILLED INTO THE A.V. A LITTLE BIT. BASED ON
WHAT HAPPENED YESTERDAY...MANY COASTAL AND VALLEY AREAS COULD REMAIN
MOSTLY CLOUDY ALL DAY...ESPECIALLY IN VENTURA AND LA COUNTY.

MIDNIGHT CREW EXTENDED THE WIND ADVISORIES FOR THE A.V. THROUGH
THURSDAY EVENING. EVEN THOUGH GRADIENTS WEAKEN SLIGHTLY
TOMORROW...MOS GUIDANCE ACTUALLY SHOWS SIMILAR OR SLIGHTLY STRONGER
WINDS IN THE DESERT TOMORROW...SO THE EXTENSION LOOKS LIKE A GOOD
CALL. SHOULD ALSO CONSIDER A LOW END WIND ADVISORY FOR THE LA
MOUNTAINS TOMORROW FOR SW WINDS...BUT WILL LIKELY STAY JUST BELOW
CRITIERIA OR SAY LOCAL GUSTS TO 45 MPH.

MAIN FOCUS FOR TODAY WILL OBVIOUSLY BE TRYING TO NAIL DOWN THE
PRECIP AND THUNDERSTORM FORECAST FOR LATE TONIGHT THROUGH FRIDAY
EVENING. AT FIRST GLANCE...FORECAST LOOKS TO BE IN GOOD SHAPE.
HOWEVER...MODELS NOT SHOWING QUITE AS MUCH INSTABILITY TODAY. NAM IS
SHOWING ABOUT 500-1000 J/KG OF CAPE TOMORROW...AS OPPOSED TO ABOUT
1500 J/KG THAT IT WAS SHOWING YESTERDAY. ALSO NOTICED THAT MODELS
ARE ACTUALLY SHOWING HIGHER QPF AMOUNTS OVER THE MOUNTAINS ON FRIDAY
THAN THEY ARE ON THURSDAY...SO WILL TAKE A CLOSER LOOK AT THAT.

***FROM PREVIOUS DISCUSSION***

WATER VAPOR IMAGERY INDICATES A MUCH STRONGER AND COLDER TROUGH OF
LOW PRESSURE OVER THE PACIFIC NORTHWEST. THIS TROUGH WILL DIG
SOUTH INTO THE STATE...BOTTOMING OUT OVER THE AREA ON THURSDAY
NIGHT. A COLD AIR MASS ALOFT MOVING IN WITH THE TROUGH WILL BRING
A CHANCE OF SHOWERS AND THUNDERSTORMS. NAM-WRF SOLUTIONS CONTINUE
TO BE AGGRESSIVE BUT LESS PROGRESSIVE WITH THE TROUGH AS IT MOVE
SOUTH INTO THE AREA. 500 MB TEMPERATURES COOL TO NEAR -28 DEGREES
CELSIUS. CAPE VALUES APPROACH BETWEEN 800-1000 J/KG ALONG THE LOS
ANGELES COUNTY COAST WITH LIFTED INDEX VALUES NEAR -4. WHILE THE
SYSTEM IS SOMEWHAT MOISTURE STARVED...THE SYSTEM SHOULD PICKUP
MOISTURE AS IT SCOOPS UP MOISTURE FROM THE PACIFIC OCEAN OVER
SOUTHERN CALIFORNIA. BECAUSE OF THE SYSTEMS CONVECTIVE
NATURE...QPF AMOUNTS WILL VARY WITH SOME LOCATIONS PICKING UP
HIGHER TOTALS THAN OTHER LOCATIONS. POPS...QPF...AND SNOW AMOUNTS
HAVE BEEN BUMPED UP OVER THE PREVIOUS FORECAST. A SPECIAL WEATHER
STATEMENT HAS BEEN ISSUED FOR THE STORM SYSTEM HIGHLIGHTING THE
POTENTIAL SHOWERS AND THUNDERSTORMS OVER THE AREA...HAIL...AND THE
POSSIBILITY OF ISOLATED WATERSPOUTS OVER THE COASTAL WATERS. A
WINTER WINTER ADVISORY MAY BE NEEDED FOR THIS SYSTEM AND COULD BE
ISSUED WITHIN THE 12 TO 18 HOURS FOR THE POSSIBILITY OF SNOW ABOVE
5000 FEET.

GFS AND ECMWF SOLUTIONS ARE BIT MORE PROGRESSIVE WITH THE TROUGH
RELATIVE TO NAM-WRF SOLUTIONS. WITH SPRING CUTOFF LOWS DROPPING
THROUGH THE REGION...A TIP OF THE CAP SHOULD BE GIVEN TO THE NAM-
WRF SOLUTIONS...USUALLY HANDLING THE MOVEMENT OF CUTOFF LOWS
RELATIVE TO THE GFS SOLUTIONS. WITH THE NAM-WRF SOLUTIONS IN
MIND...SLIGHT CHANCE POPS WERE EXTENDED INTO FRIDAY EVENING FOR
THE SOUTHERN AREAS. 06Z NAM-WRF SOLUTIONS ARE CONSISTENT AND
INLINE WITH THE 00Z SOLUTIONS IN LINGERING THE TROUGH OVER THE
REGION INTO FRIDAY.

.LONG TERM (SATURDAY-TUESDAY)...

HIGH PRESSURE ALOFT SHOULD BUILD IN FOR THE WEEKEND BRINGING A
WARMING TREND FOR THE WEEKEND AND INTO NEXT WEEK. WITH MUCH
DETAIL PLACED INTO THE SHORT-TERM PERIOD...LITTLE CHANGES WERE
MADE...EXCEPT TO ADD SOME MARINE LAYER STRATUS FOR TUESDAY
MORNING AS ONSHORE FLOW STRENGTHEN BENEATH SOUTHWEST FLOW ALOFT.

&&

.AVIATION...06/18Z...

AT 1750Z AT KLAX... THE INVERSION WAS BASED AT 5400 FEET. THE TOP OF
THE INVERSION WAS 7300 FEET WITH A TEMPERATURE OF 6 DEGREES CELSIUS.

OVERALL...MODERATE CONFIDENCE IN THE 18Z TAFS WITH THE REDUCED
CONFIDENCE DUE TO UNCERTAINTY IN HOW MUCH THE MARINE INTRUSION WILL
DIMINISH AND WHEN.  BUT WITH SUCH A HIGH INVERSION MOST LOCATIONS
ARE ALREADY IN VFR CONDITIONS EVEN IF THEY DO NOT CLEAR TODAY.  THE
EXCEPTIONS ARE KPRB AND KSBP WHERE CIGS ARE NEAR 2000 FEET BUT ARE
EXPECTED TO BOTH RISE AND DIMINISH IN THE NEXT FEW HOURS.  CIGS WILL
LOWER AGAIN OVERNIGHT BUT ARE NOT EXPECTED TO DROP BELOW MVFR
CONDITIONS DURING THE FORECAST PERIOD.  KPMD AND KWJF WILL BE WINDY
BUT REMAIN CAVU THROUGHOUT THE FORECAST PERIOD.

KLAX...MODERATE CONFIDENCE IN THE 18Z TAF WITH THE REDUCED
CONFIDENCE DUE TO UNCERTAINTY IN HOW MUCH THE MARINE INTRUSION WILL
DIMINISH AND WHEN.  WITH SUCH A HIGH INVERSION... CIGS WILL REMAIN
UP IN VFR CONDITIONS EVEN IF THEY DO NOT CLEAR TODAY.  CIGS WILL
LOWER AGAIN OVERNIGHT BUT ARE NOT EXPECTED TO DROP BELOW MVFR
CONDITIONS DURING THE FORECAST PERIOD. THERE IS A 30% CHANCE THAT
VFR CIGS WILL NOT DISSIPATE THIS AFTERNOON.

KBUR...MODERATE CONFIDENCE IN THE 18Z TAF WITH THE REDUCED
CONFIDENCE DUE TO UNCERTAINTY IN HOW MUCH THE MARINE INTRUSION WILL
DIMINISH AND WHEN.  WITH SUCH A HIGH INVERSION... CIGS WILL REMAIN
UP IN VFR CONDITIONS EVEN IF THEY DO NOT CLEAR TODAY.  CIGS WILL
LOWER AGAIN OVERNIGHT BUT ARE NOT EXPECTED TO DROP BELOW MVFR
CONDITIONS DURING THE FORECAST PERIOD. THERE IS A 30% CHANCE THAT
VFR CIGS WILL NOT DISSIPATE THIS AFTERNOON.

&&

.MARINE...06/830 AM.

FOR THE OUTER WATERS...HIGH CONFIDENCE IN NORTHWEST WINDS REMAINING
AT SMALL CRAFT ADVISORY LEVELS THROUGH THURSDAY EVENING. THE WINDS
WILL DIMINISH TO BELOW ADVISORY LEVELS ON FRIDAY AND SATURDAY BUT
WILL STRENGTHEN AGAIN ON SUNDAY WITH A CHANCE OF REACHING SMALL
CRAFT ADVISORY LEVELS.

FOR THE INNER WATERS...
NORTH OF POINT CONCEPTION THERE IS MODERATE CONFIDENCE IN NORTHWEST
WINDS REACHING SMALL CRAFT ADVISORY LEVELS THIS AFTERNOON AND
EVENING THEN THE WIND WILL DIMINISH THROUGH THE WEEKEND.

SOUTH OF POINT CONCEPTION THERE IS HIGH CONFIDENCE IN WEST TO
NORTHWEST WINDS REMAINING BELOW SMALL CRAFT ADVISORY LEVELS THROUGH
THE WEEKEND ALTHOUGH THERE IS A 30% CHANCE OF SMALL CRAFT LEVEL
GUSTS ACROSS THE WESTERN HALF OF THE SANTA BARBARA CHANNEL.

OVERALL... THERE IS A SLIGHT CHANCE OF SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS ACROSS THE COASTAL WATERS ON THURSDAY AND
FRIDAY MOVING DOWN FROM THE NORTH. ANY THUNDERSTORMS WOULD BE
CAPABLE OF PRODUCING BRIEF HEAVY RAIN... GUSTY AND ERRATIC WINDS...
ROUGH SEAS... AND A POSSIBLE WATERSPOUT.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY (SEE LAXNPWLOX).
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
HIGH SURF ADVISORY (SEE LAXCFWLOX).
SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).

&&
$$

PUBLIC...SUKUP/HALL
AVIATION...KJ
MARINE...KJ
SYNOPSIS...DSS

WWW.WEATHER.GOV/LOSANGELES





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.