916
FXUS66 KLOX 151625
AFDLOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
925 AM PDT MON SEP 15 2025
SYNOPSIS
15/904 AM.
A WARMING TREND WILL CONTINUE THROUGH AT LEAST TUESDAY AS HIGH
PRESSURE ALOFT OVER NORTHERN MEXICO BUILDS OVER THE REGION.
ONSHORE FLOW REMAINING IN PLACE ACROSS THE AREA WILL KEEP AREAS
OF NIGHT THROUGH MORNING LOW CLOUDS AND FOG IN THE FORECAST FOR
MANY COAST AND COASTAL VALLEY AREAS THROUGH TUESDAY. A MONSOONAL
FLOW PATTERN WILL DEVELOP BETWEEN TUESDAY AND WEDNESDAY AND BRING
THE POSSIBILITY OF SHOWERS AND THUNDERSTORMS FOR THE MID-TO-LATE
WEEK. A VERY WARM AND HUMID AIR MASS IS LIKELY TO SETTLE INTO THE
REGION DURING THIS PERIOD.
SHORT TERM (TDY-WED)
15/923 AM.
***UPDATE***
THE MARINE LAYER DID LOWER OVERNIGHT SOUTH OF PT CONCEPTION TO
BETWEEN 1500 AND 2000 FEET AS HIGH PRESSURE TRIES TO BUILD OVER
THE AREA. WITH THAT AND A WEAKER ONSHORE FLOW TEMPERATURES ARE
EXPECTED TO WARM UP DAY AWAY FROM THE COAST BY 3-6 DEGREES ON
AVERAGE. ALONG THE CENTRAL COAST THERE GRADIENTS ARE TRENDING
ONSHORE FLOW AND THE NORTHEAST FLOW ALOFT IS MUCH WEAKER THAN
YESTERDAY SO SOME COOLING IS EXPECTED THERE.
MOISTURE FROM TS MARIO WILL CONTINUE TO WORK ITS WAY NORTH AND
PW'S WILL BE ON THE RISE AS EARLY AS TUESDAY, BUT PEAKING LATE
WEDNESDAY INTO THURSDAY WHEN OUR AREA WILL BE AT THE GREATEST RISK
FOR SHOWERS AND THUNDERSTORMS. SOME MODELS TODAY HAVE SHIFTED THE
PATH OF THE MARIO REMNANTS OVER VENTURA AND LA COUNTIES DURING
THAT TIME BUT STILL LOW CONFIDENCE ON THAT. THE MAIN MESSAGE
REMAINS THE SAME WITH A CHANCE OF SHOWERS AND STORMS REGION-WIDE
AS EARLY AS WEDNESDAY. WE ALSO HAVE INCREASING HEAT AND HUMIDITY
THAT MAY REQUIRE SOME TARGETED HEAT ADVISORIES IN LA COUNTY
WEDNESDAY ASSUMING THERE ISN'T TOO MUCH CLOUD COVER BY THEN. NOT
PLANNING TO ISSUE ANY ADVISORIES TODAY DUE TO THE UNCERTAINTY AND
WILL RE-EVALUATE TUESDAY.
***FROM PREVIOUS DISCUSSION***
THE LOW CLOUD FIELD WILL LIKELY BECOME MORE PROBLEMATIC OVER THE
COMING DAYS AS HIGH PRESSURE ALOFT BUILDS INTO THE REGION AND A
MONSOONAL FLOW PATTERN STARTS TO SHAPE UP. THE LATEST SATELLITE
IMAGERY SHOWS AN UPPER-LEVEL RIDGE OVER NORTHERN MEXICO EARLY THIS
MORNING. THIS RIDGE WILL BUILD OVER THE REGION INTO TUESDAY NIGHT
AND EXPAND INTO THE GREAT BASIN FOR WEDNESDAY. A WARMING TREND
WILL CONTINUE OVER THE AREA THROUGH AT LEAST TUESDAY AS 500 MB
HEIGHTS CLIMB THROUGH TUESDAY NIGHT. ONSHORE FLOW WILL WEAKEN AND
SUBSIDING AIR ALOFT WILL PRESS DOWN ON TOP OF THE MARINE INTRUSION
AND FIT IT INTO A SMALLER AREA. AS A RESULT, LESS LOW CLOUD
COVERAGE IS EXPECTED OVER THE COMING DAYS, AND TEMPERATURES WILL
RISE EVEN FURTHER. THE LATEST HEAT RISK PARAMETERS SUGGEST THE
SITUATION TO BE MARGINAL FOR HEAT ADVISORY HEADLINES, BUT THIS
WILL NEED TO BE CLOSELY WATCHED. HIGHER CONFIDENCE EXISTS IN THE
TEMPERATURE FORECAST THROUGH TUESDAY, BUT LESS CONFIDENCE EXISTS
IN THE WARMING TREND CONTINUING FOR WEDNESDAY DUE TO INCREASE IN
MONSOONAL MOISTURE.
INCREASING MONSOONAL MOISTURE WILL START TO SPREAD INTO THE REGION
BETWEEN TUESDAY AND WEDNESDAY AS SOUTHEAST FLOW ALOFT ESTABLISHES.
MOISTURE FROM REDEVELOPING TROPICAL STORM MARIO WILL BECOME
EMBEDDED WITH THE MONSOONAL FLOW AND GET TRANSPORTED INTO SOUTHERN
CALIFORNIA BETWEEN TUESDAY AND WEDNESDAY. AS IS FREQUENT WITH
THESE PATTERNS, THERE IS A GREAT AMOUNT OF UNCERTAINTY HOW MUCH
PRECIPITATION AND CLOUD COVERAGE WILL OCCUR. A DENSE CLOUD SHIELD
WITH THE INCREASE IN MOISTURE COULD CUT INTO TEMPERATURES ON
WEDNESDAY AND THURSDAY. LOW CONFIDENCE SHOULD BE EXERCISED IN THE
FORECAST FOR PRECIPITATION AS CONVECTIVE ACTIVITY BE COULD MORE
OR LESS WIDESPREAD THAN INDICATED. THE FORECAST REMAINS CONSISTENT
FOR NOW WITH A BLANKET SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS
BETWEEN AFTER WEDNESDAY, BUT THERE IS A MODERATE CHANCE THAT THE
MOISTURE COULD ARRIVE AS SOON AS TUESDAY AFTERNOON OR TUESDAY NIGHT.
NBM VALUES TREND WETTER FOR POPS, AND THAT COULD CERTAINLY
DEVELOP, BUT GIVEN HOW THE NBM HAS STRUGGLED WITH THE LAST SEVERAL
EVENTS, THE FORECAST REMAINS CONSISTENT FOR NOW. AS THE MOISTURE
ARRIVES ON TUESDAY NIGHT OR WEDNESDAY, THERE IS A MODERATE CHANCE
THAT A PERIOD OF DRY THUNDERSTORMS COULD DEVELOP, OR THUNDERSTORMS
THAT CONTAIN LITTLE TO NO RAINFALL DUE TO THE DRY AIR MASS
BENEATH THE MOISTURE.
MOISTURE WILL VERY LIKELY CONTINUE TO SPREAD INTO THE REGION
THROUGH WEDNESDAY NIGHT AND THURSDAY. EPS AND GEFS PRECIPITABLE
WATER VALUE MEANS APPROACH 1.75 INCHES BY LATE WEDNESDAY NIGHT, OR
VALUES ABOVE THE 97TH PERCENTILE. THIS IS WHEN THE AIR MASS COULD
TURN WETTER AND ADD THE POTENTIAL FOR FLOODING. BRIEF HEAVY
DOWNPOURS WILL CERTAINLY BE POSSIBLE AS SOON AS WEDNESDAY
AFTERNOON OR EVENING WITH ANY SHOWERS OR THUNDERSTORMS.
LONG TERM (THU-SUN)
15/318 AM.
THE PATTERN COULD TURN MORE ACTIVE BETWEEN EARLY THURSDAY AND
FRIDAY NIGHT. THE LATEST DETERMINISTIC SOLUTIONS ARE STRUGGLING
WITH MODELING OF THE REMNANT CIRCULATION OF MARIO, GFS SOLUTIONS
PUSH IT NORTH INTO ALONG THE CENTRAL COAST, WHILE NAM-WRF
SOLUTIONS BRING THE CENTER OF THE CIRCULATION INTO THE LOS ANGELES
BASIN. WHILE THERE IS UNCERTAINTY WITH THE ACTUAL MOVEMENT, THERE
IS GOOD AGREEMENT ACROSS THE FORECAST ENSEMBLE FOR THE MOISTURE
TO BE IN PLACE. A VAST MAJORITY OF THE EPS AND GEFS SOLUTIONS ARE
SUGGESTING THE MOST LIKELY PERIOD FOR RAINFALL FROM SHOWERS AND
THUNDERSTORMS TO OCCUR BETWEEN EARLY THURSDAY AND FRIDAY NIGHT.
THE FORECAST CONTINUES CHANCE POPS ACROSS THE REGION, BUT FUTURE
SHIFTS MAY NEED TO CONSIDER UPPING POPS INTO THE LIKELY CATEGORY.
ALL FORECAST ENSEMBLE MEMBERS SUGGEST THE PRECIPITABLE WATER
VALUE MEANS REACHING MAXIMUM ON THURSDAY MORNING, THEN MOISTURE
RECEDING THEREAFTER. CHANCES OF SHOWERS AND THUNDERSTORMS WILL
COULD LINGER INTO FRIDAY OR SATURDAY, THEN BECOME CONFINED TO THE
MOUNTAINS AND DESERT OVER THE WEEKEND.
WHILE TEMPERATURES WILL COOL WITH THE INCREASE IN MOISTURE AND
THE POTENTIAL FOR SHOWER ACTIVITY, TEMPERATURES WILL LIKELY REMAIN
WARM AND HUMID INTO LATE WEEK.
AVIATION
15/1127Z.
AT 1025Z AT KLAX, THE MARINE LAYER WAS 1700 FT DEEP. THE TOP OF
THE INVERSION WAS AT 3400 FT WITH A TEMPERATURE OF 24 C.
HIGH CONFIDENCE IN KPMD AND KWJF TAFS.
LOW CONFIDENCE IN TAFS FOR KSMX AND KSBP. THERE IS A 40% CHANCE
OF NO LOW CLOUDS AT KSMX AND A 40% CHANCE OF BRIEF CIGS AT KSBP
THROUGH 17Z.
MODERATE CONFIDENCE IN REMAINING TAFS. TIMING OF FLIGHT CAT
CHANGES MAY BE OFF BY 2 HOURS AND FLIGHT CAT MAY BE OFF BY ONE AT
TIMES. CIGS MAY SCATTER OUT AND REFORM AT TIMES THROUGH 12Z. 30%
CHANCE FOR LIFR TO IFR CIGS AT KPRB, KBUR AND KVNY AFTER 08Z
TUES.
KLAX...MODERATE CONFIDENCE IN TAF. CLEARING TIMES MAY BE OFF BY 2
HOURS. THERE IS A 15% CHANCE THAT THERE IS NO VFR TRANSITION
THROUGH THE PERIOD OR IS VERY BRIEF. NO SIGNIFICANT EAST WIND
COMPONENT EXPECTED THROUGH THE PERIOD.
KBUR...MODERATE CONFIDENCE IN TAF. CLEARING TIMES MAY BE OFF BY 2
HOURS. 30% CHANCE FOR LIFR TO IFR CIGS AT KBUR AFTER 08Z TUES.
MARINE
15/839 AM.
MINIMAL RISKS OF SMALL CRAFT ADVISORY (SCA) WINDS THROUGH
WEDNESDAY NIGHT, EXCEPT FOR A 30% CHANCE OF LOW-END SCA WINDS OFF
THE CENTRAL COAST WEDNESDAY AFTERNOON AND EVENING.
MOISTURE AND ENERGY FROM THE REMNANTS OF WHAT IS CURRENTLY
TROPICAL STORM MARIO WILL IMPACT SOUTHWEST CALIFORNIA WEDNESDAY
THROUGH THURSDAY OR FRIDAY. A PERIOD OF SHOWERS IS LIKELY AT SOME
TIME, WITH THURSDAY HAVING THE HIGHEST CHANCES, BUT CONFIDENCE IS
FAIRLY LOW ON TIMING AND AMOUNTS. THUNDERSTORMS ARE ALSO POSSIBLE
AT ANY TIME IN THE TIME WINDOW, BUT AGAIN CONFIDENCE IS LOW ON
THE DETAILS. ANY THUNDERSTORM WILL BRING A RISK OF BRIEF BUT
STRONG WINDS AND FREQUENT LIGHTNING. IN ADDITION, GUSTY SANTA ANA-
LIKE WINDS ARE POSSIBLE ON THURSDAY DUE TO THE PROXIMITY OF THE
CORE OF THE WEAKENED STORM. PLEASE MONITOR THE FORECAST IF YOU
HAVE ANY PLANS ON GOING OUT ON THE WATER THIS WEEK, AS THIS WILL
BE A LOW- CONFIDENCE AND EVOLVING SITUATION.
LOX WATCHES/WARNINGS/ADVISORIES
CA...BEACH HAZARDS STATEMENT IN EFFECT THROUGH LATE TUESDAY NIGHT
FOR ZONES 354-362-366. (SEE LAXCFWLOX).
PZ...NONE.
PUBLIC...MW/HALL
AVIATION...LEWIS
MARINE...LEWIS/KITTELL
SYNOPSIS...HALL
WEATHER.GOV/LOSANGELES
EXPERIMENTAL GRAPHICAL HAZARDOUS WEATHER OUTLOOK AT:
HTTPS://WWW.WEATHER.GOV/ERH/GHWO?WFO=LOX
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page