Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 290335 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
835 PM PDT TUE JUL 28 2015

.SYNOPSIS...

A LARGE HIGH PRESSURE SYSTEM WILL BRING VERY WARM AND HUMID
CONDITIONS THROUGH EARLY NEXT WEEK. THIS COMBINATION WILL CREATE A
SLIGHT CHANCE OF THUNDERSTORM AND SHOWER ACTIVITY FOR THE MOUNTAINS
AND DESERTS FROM WEDNESDAY INTO EARLY NEXT WEEK. THE STORM ACTIVITY
WILL REACH INTO SOME OF THE COASTAL AND VALLEYS AREAS ON THURSDAY.

&&

.UPDATE...

THE LATEST SATELLITE IMAGERY INDICATES A HIGH PRESSURE SYSTEM
CENTERED ALONG THE OKLAHOMA-ARKANSAS BORDER THIS EVENING. OVER
SOUTHERN CALIFORNIA...DRY SOUTHWEST FLOW ALOFT CONTINUES TO WEAKEN.
MODEL SOLUTIONS REMAIN IN GOOD AGREEMENT WITH HIGH PRESSURE
EXPANDING WESTWARD AND BUILDING INTO THE GREAT BASIN THROUGH
THURSDAY. WEAKENING SOUTHWEST FLOW ALOFT THIS EVENING WILL BE
REPLACED BY SOUTHEAST FLOW ALOFT BY LATE WEDNESDAY MORNING. THIS
WILL ALLOW FOR MONSOONAL MOISTURE OVER THE SONORAN DESERT TO SPILL
INTO SOUTHERN CALIFORNIA WEDNESDAY.

NAM AND GFS SOLUTIONS CONTINUE TO KEEP A DECENT MOISTURE SURGE
DEVELOPING BETWEEN WEDNESDAY NIGHT AND THURSDAY MORNING. THE LATEST
NAM-WRF SOLUTIONS ADVECT A VORTICITY MAXIMUM NORTHWEST INTO
SOUTHWEST CALIFORNIA AND MOVING FROM LOS ANGELES COUNTY ON THURSDAY
MORNING TO THE SAN LUIS OBISPO COUNTY BY THURSDAY AFTERNOON OR
EVENING. WITH GFS SOLUTIONS OFFERING A SIMILAR SCENARIO AND OFFERING
UP INCREASED POPS IN THE LATEST GFS MOS GUIDANCE...AND RUN-TO-RUN
CONSISTENCY IN THE LATEST NAM-WRF SOLUTIONS...POPS WERE TRENDED
HIGHER AREAWIDE FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY NIGHT.
THERE IS A FAVORABLE CHANCE FOR CONVECTION SPILLING OVER THE COAST
AND VALLEYS ON THURSDAY. CLOUD COVERAGE WAS ALSO BUMPED UP FOR THE
ENTIRE AREA...MAKING THURSDAY PARTLY TO MOSTLY CLOUDY ACROSS THE
AREA. WITH MORE CLOUDS THAN SUN...TEMPERATURES WERE NUDGED DOWN FOR
THURSDAY BUT STILL COULD VASTLY OVERDONE IF THE DAY IS CLOUDY. MODEL
SOLUTIONS HINT AT COOLER DAY ON THURSDAY AND TEMPERATURES FOLLOW
SUIT. WHILE THE AIR MASS WILL BE MOIST...ANY STORM THAT DEVELOP
THURSDAY WILL BE MOVING QUITE RAPIDLY AS 500 MB WINDS LOOK TO BE
ABOUT 25 TO 30 KNOTS. AT THIS TIME...THE MAIN THREAT WILL BE
TRAINING STORMS CREATING FLASH FLOODING...ISOLATED DRY
THUNDERSTORMS...AND DANGERS FROM LIGHTNING IN GENERAL.

AN ADDITIONAL UPDATE IS PLANNED TO TWEAK TEMPERATURES FOR WEDNESDAY
AT THIS TIME.

&&


.PREV DISCUSSION...

SHORT TERM...THE SYNOPTIC PICTURE REMAINS ESSENTIALLY UNCHANGED ON
FRIDAY WITH HEIGHTS REMAINING AROUND 591 DM. THU AND FRI WILL BE THE
TWO WARMEST DAYS WITH MAX TEMPS 4 TO 8 DEGREES ABOVE NORMAL
EVERYWHERE EXCEPT THE IMMEDIATE COAST. THERE WILL BE ENOUGH
ADDITIONAL HUMIDITY TO RAISE THE HEAT INDEX VALUES CLOSE TO ADVISORY
LEVELS ALTHOUGH RIGHT NOW IT ONLY LOOKS LIKE A FEW ISOLATED SPOTS
WILL ACTUALLY MEET OR EXCEED THESE THRESHOLDS.

LONG TERM...VERY LITTLE CHANGE OVER THE EXTENDED PERIOD. LONG RANGE
MODELS AND ENSEMBLES SHOW THE 4 CORNERS HIGH REMAINING NEARLY
STATIONARY. IT EXPANDS A LITTLE WHICH TURNS THE FLOW OVER OUR AREA
TO A MORE SOUTHERLY DIRECTION WHICH IS NOT QUITE AS CONDUCIVE TO
THUNDERSTORM FORMATION. ONSHORE FLOW INCREASES A LITTLE BY THE
WEEKEND WHICH SHOULD BRING SOME COOLING BUT MOSTLY NEAR THE COASTS
AND COASTAL VALLEY LOCATIONS.

&&

.AVIATION...29/0000Z.

AT 00Z...THE MARINE LAYER DEPTH AT LAX WAS AROUND 1000 FEET DEEP.
THE TOP OF THE INVERSION WAS LOCATED AROUND 4600 FEET WITH A
TEMPERATURES OF 25 DEGREES CELSIUS.

MODERATE TO HIGH CONFIDENCE IN LIFR TO IFR CONDITIONS WILL SPREAD
INTO COASTAL TERMINALS THROUGH 10Z. THERE IS A CHANCE OF LIFR TO IFR
CONDITIONS FOR LOS ANGELES VALLEY TERMINALS. IFR CONDITIONS COULD
LIFT INTO THE MVFR CATEGORY BETWEEN 10Z AND 15Z FOR TERMINALS SOUTH
OF POINT CONCEPTION. THERE IS A CHANCE OF IFR TO MVFR CONDITIONS
LINGERING INTO WEDNESDAY AFTERNOON.

KLAX...IFR CONDITIONS WILL SPREAD INTO KLAX BETWEEN 04Z AND 08Z.
THERE IS A 40 PERCENT CHANCE OF CONDITIONS REMAINING IFR THROUGH
14Z. KLAX SHOULD CLEAR OUT LATER ON WEDNESDAY WITH A 30
PERCENT CHANCE OF IFR TO MVFR CONDITIONS LINGERING UNTIL 20Z.

KBUR...THERE IS A 40 PERCENT CHANCE OF VFR CONDITIONS THROUGHOUT THE
PERIOD.

&&

.MARINE...28/900 PM.

SMALL CRAFT ADVISORY CONDITIONS ARE NOT EXPECTED THROUGH THURSDAY.
THERE IS A CHANCE OF SMALL ADVISORY LEVEL WINDS WITH WEST-NORTHWEST
WINDS IN THE VICINITY OF POINT CONCEPTION TO SAN NICOLAS ISLAND
FRIDAY AFTERNOON AND NIGHT. A BETTER CHANCE EXISTS FOR SMALL CRAFT
ADVISORY LEVELS WINDS EXISTS ON SATURDAY AFTERNOON AND NIGHT.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).

&&

$$

PUBLIC...JLD
AVIATION...HALL
MARINE...HALL/30
SYNOPSIS...SETO/HALL

WWW.WEATHER.GOV/LOSANGELES


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