Area Forecast Discussion
Issued by NWS Los Angeles, CA

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000
FXUS66 KLOX 280205 AAA
AFDLOX

SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
705 PM PDT MON JUL 27 2015

UPDATED SYNOPSIS AND AVIATION SECTION

.SYNOPSIS...

A HIGH PRESSURE SYSTEM WILL BRING A COMBINATION OF MOIST AIR AND
ABOVE NORMAL TEMPERATURES TO THE REGION THROUGH EARLY NEXT
WEEK...THEN A COOLING TREND SHOULD BEGIN. THIS COMBINATION WILL
GENERATE A SLIGHT CHANCE OF THUNDERSTORMS AND SHOWERS FOR THE
MOUNTAIN AND DESERT AREAS FROM WEDNESDAY INTO EARLY NEXT WEEK. THE
STORM ACTIVITY WILL ALSO REACH THE COASTAL AND VALLEYS AREAS FROM
LATE WEDNESDAY TO FRIDAY.

&&

.SHORT TERM (TODAY-FRI)... AN UPPER LEVEL TROUGH CURRENTLY PUSHING
THROUGH IDAHO WILL PUSH THROUGH MONTANA ON TUESDAY. THIS WILL CREATE
A WEAK BUT LARGE SURFACE HIGH CENTERED OVER SOUTHEAST IDAHO WHICH
WILL GREATLY WEAKEN ONSHORE PRESSURE GRADIENTS OVER OUR AREA TONIGHT
AND PERSIST THROUGH FRIDAY. WE COULD EVEN SEE SOME LIGHT OFFSHORE
FLOW OVER SBA AND SLO COUNTIES...ESPECIALLY IF THE GFS PROJECTIONS
ARE TRUER THAN THE NAM. MEANWHILE...HIGH PRESSURE ALOFT WILL FORM
OVER CALIFORNIA BEHIND THE TROUGH...WHICH WILL PEAK ON THURSDAY AND
FRIDAY AS THE LARGE RIDGE OVER OKLAHOMA SLIDES INTO NORTHWEST NEW
MEXICO. THIS ALL ADDS UP TO A HEALTHY WARM UP...WITH A SIGNIFICANT
JUMP STARTING TOMORROW...THEN ANOTHER ON THURSDAY. BY
THURSDAY...MOST AREAS WILL BE IN THE 90S WITH THE WARMEST VALLEY
LOCATIONS SEEING LOW TRIPLE DIGITS. COASTAL AREAS WILL BE LARGELY
DEPENDENT ON HOW THE MARINE LAYER RESPONDS...WHICH BY ALL INDICATION
SHOULD DISSIPATE ON BY THURSDAY. WITH HUMIDITY ON THE RISE THROUGH
THE PERIOD AS WELL...IT WILL FEEL A TOUCH WARMER THAN THE
THERMOMETER READS ON THURSDAY AND FRIDAY...AND THE ASSOCIATED HEAT
INDEX VALUES MAY APPROACH EXCESSIVE HEAT THRESHOLDS FOR THE VALLEYS
AND MOUNTAINS. AT THIS POINT...IT DOES NOT LOOK LIKE THOSE
THRESHOLDS WILL BE MET OVER A LARGE ENOUGH AREA TO WARRANT AN
EXCESSIVE HEAT WATCH...BUT IF THE FORECAST TRENDS WARMER STILL...WE
MAY NEED ONE.

THE ADDED HUMIDITY WILL BE A RESULT OF THE LARGE RIDGE OVER OKLAHOMA
SLIDING WESTWARD...RESULTING IN MOIST SOUTHEAST FLOW ALOFT. THIS
MONSOONAL FLOW SHOULD ARRIVE QUICKLY ON WEDNESDAY...AND PERSIST
THROUGH THE WEEK...WITH THE JUICIEST AIR ON THURSDAY AND FRIDAY.
WITH THIS MOISTURE...AND THE VERY HOT TEMPERATURES OVER THE
INTERIOR...SHOWERS AND THUNDERSTORMS WILL BECOME MORE LIKELY. ON
WEDNESDAY WITH THE INITIAL ARRIVAL...THE 1.2 INCH PWATS ARE NOT
CONDUCIVE TO FLASH FLOODING AND DRY LIGHTNING WILL BE POSSIBLE. BY
WEDNESDAY NIGHT AND THURSDAY HOWEVER...PWATS JUMP UP TO 1.6 INCHES
WITH STEERING FLOW BELOW 10 KTS. THESE TWO INGREDIENTS ALONE
HIGHLIGHT THE SIGNIFICANT POTENTIAL FOR FLASH FLOODING...AND IF THIS
WERE EXPECTED TOMORROW...WE WOULD PROBABLY HAVE A FLASH FLOOD WATCH
OUT NOW. IN ADDITION TO THE INTERIOR SECTIONS HAVING A 20-30 PERCENT
CHANCE FOR THUNDERSTORMS...SOME COASTAL AND VALLEY AREAS ALSO HAVE A
SLIGHT CHANCE FOR THURSDAY AND FRIDAY...ALTHOUGH WEDNESDAY CANNOT BE
COUNTED OUT EITHER.

.LONG TERM (SAT-MON)... THE RIDGE OF HIGH PRESSURE PARKED OVER NEW
MEXICO ON FRIDAY WILL SLIDE TO THE NORTH AND EAST OVER THE
WEEKEND...WITH THE FLOW SHIFTING TO SOUTHWESTERLY ALOFT BY SUNDAY OR
MONDAY. WHEN THIS HAPPENS...THE THUNDERSTORM POTENTIAL WILL QUICKLY
DECLINE...AND TEMPERATURES WILL LOWER AS ONSHORE FLOW RETURNS.
STILL...THERE IS A SLIGHT CHANCE FOR THUNDERSTORMS OVER THE INTERIOR
AREAS ON SATURDAY AND POSSIBLY SUNDAY AS THE FLOW SLOWLY SHIFTS.

&&

.AVIATION...28/0000Z.

AT 0000Z...THE MARINE INVERSION AT KLAX WAS BASED AROUND 1700 FEET.
THE TOP OF THE INVERSION WAS AROUND 2600 FEET WITH A TEMPERATURE OF
21 DEGREES CELSIUS.

MODERATE CONFIDENCE IN THE CURRENT FORECAST. IFR TO MVFR CONDITIONS
WILL LIKELY SPREAD INTO COASTAL TERMINALS THROUGH 10Z. THERE IS A
CHANCE OF IFR TO MVFR CONDITIONS AT VALLEY TERMINALS BETWEEN 10Z AND
15Z. NORTH OF POINT CONCEPTION...THERE IS A CHANCE OF VLIFR TO LIFR
CONDITIONS AT CENTRAL COAST TERMINALS BETWEEN 04Z AND 15Z.

KLAX...MVFR CONDITIONS COULD DEVELOP AS SOON AS 03Z...OR AS LATE AS
10Z. HIGHER CONFIDENCE EXISTS IN A LATER ARRIVAL TIME BETWEEN 08Z
AND 10Z. THERE IS A 40 PERCENT CHANCE OF IFR CONDITIONS. VFR
CONDITIONS COULD DEVELOP AS SOON AS 16Z...OR AS LATE AS 18Z. THERE
IS

KBUR...VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD...EXCEPT FOR
A 30 PERCENT CHANCE OF IFR TO MVFR CONDITIONS BETWEEN 10Z AND 16Z.

&&

.MARINE...27/200 PM.

FOR THE OUTER WATERS...MODERATE TO HIGH CONFIDENCE THAT SCA CONDS
WILL CONTINUE THROUGH LATE TONIGHT...THEN WINDS WILL DECREASE BELOW
SCA LEVELS...AND LIKELY REMAIN BELOW SCA LEVELS THROUGH THE WEEK.

FOR THE INNER WATERS..VERY GOOD CONFIDENCE IN CURRENT FORECAST.
THERE IS JUST A 20 PERCENT CHANCE OF SCA LEVEL WINDS THIS AFTERNOON
AND EVENING ACROSS NORTHERN SECTIONS OF THE INNER WATERS AND
WESTERN PORTIONS OF THE SANTA BARBARA CHANNEL.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY (SEE LAXMWWLOX).
SPECIAL WEATHER STATEMENT (SEE LAXSPSLOX).

&&

$$

PUBLIC...KITTELL
AVIATION...HALL
MARINE...KAPLAN/RORKE
SYNOPSIS...SETO/HALL

WWW.WEATHER.GOV/LOSANGELES


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