889
FXUS66 KLOX 202103
AFDLOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA
103 PM PST SAT DEC 20 2025
SYNOPSIS
19/452 PM.
MOSTLY CLEAR SKIES ARE EXPECTED THROUGH SATURDAY EXCEPT FOR
OVERNIGHT TO MORNING LOW CLOUDS AND FOG NEAR THE COAST. IT WILL
BE COOLER EACH DAY, BUT HIGH TEMPERATURES WILL REMAIN ABOVE
NORMAL. THERE WILL BE INCREASING CLOUDS, COOLER TEMPERATURES AND
A SLIGHT CHANCE OF RAIN OVER SAN LUIS OBISPO COUNTY SUNDAY AND
MONDAY. A STRONG STORM WILL BRING MANY INCHES OF RAIN TO THE
ENTIRE AREA TUESDAY THROUGH WEDNESDAY.
SHORT TERM (TDY-TUE)
20/102 PM.
OVERALL, 12Z MODELS IN GOOD AGREEMENT THROUGH THE SHORT TERM
PERIOD. AT UPPER LEVELS, FLOW TURNS MORE SOUTHWESTERLY THROUGH
TUESDAY. NEAR THE SURFACE, WEAK ONSHORE FLOW WILL PREVAIL THROUGH
MONDAY THEN SOUTHEASTERLY FLOW WILL INCREASE DURING THE DAY ON
TUESDAY.
FORECAST-WISE, TODAY THROUGH MONDAY LOOKS TO BE RATHER UNEVENTFUL.
WITH LOWERING H5 HEIGHTS AND ONSHORE SURFACE FLOW, THERE WILL BE
AN INCREASE IN DEPTH/COVERAGE OF THE MARINE LAYER STRATUS.
ADDITIONALLY, MID/HIGH LEVEL CLOUDS WILL BE ON THE INCREASE ACROSS
THE AREA. GIVEN THE OVERALL FLOW PATTERN, THERE WILL BE A THREAT
OF RAIN ACROSS NORTHERN SAN LUIS OBISPO COUNTY BEGINNING THIS
EVENING AND CONTINUING THROUGH MONDAY. RAIN TOTALS THROUGH MONDAY
EVENING ACROSS SLO COUNTY WILL GENERALLY BE UNDER 0.10 INCHES
ALTHOUGH SANTA LUCIA MOUNTAINS COULD RECEIVE UP TO AROUND 0.50
INCHES.
ON TUESDAY, THE HOLIDAY "FUN" WILL BEGIN AS THE AR BEGINS TO SAG
SOUTHWARD ACROSS THE AREA. STEADY LIGHT RAIN WILL BEGIN ACROSS SLO
COUNTY TUESDAY MORNING AND WILL SPREAD SOUTH INTO LA COUNTY BY
TUESDAY AFTERNOON/EVENING. THROUGH THE AFTERNOON, RAINFALL
INTENSITIES WILL BE LIGHT, BUT THE RAIN INTENSITY WILL INCREASE TO
MODERATE LEVELS TUESDAY EVENING. THROUGH TUESDAY EVENING, RAIN
TOTALS WILL GENERALLY BE AROUND 0.25 INCHES OR LESS ALTHOUGH
SOUTH-FACING SLOPES OF SBA/VENTURA COUNTIES WOULD RECEIVE 0.50 TO
0.75 INCH TOTALS. SNOW LEVELS WILL REMAIN QUITE HIGH, ABOVE 7500
FEET, THROUGH TUESDAY EVENING. ALONG WITH THE INCREASING RAIN,
SOUTHEASTERLY WINDS WILL INCREASE DURING THE DAY ON TUESDAY.
WIDESPREAD ADVISORY-LEVEL WINDS ARE LIKELY FOR MOST AREAS WITH
EVEN A CHANCE OF WARNING-LEVEL GUSTS ACROSS THE MOUNTAINS
(ESPECIALLY THE SANTA LUCIA RANGE AND THE INTERSTATE 5 CORRIDOR).
LONG TERM (WED-SAT)
20/102 PM.
FOR THE EXTENDED, ALL MODELS INDICATE SYSTEMS ARE STILL A "GO" FOR
A VERY SIGNIFICANT WINTER STORM TO IMPACT THE AREA. ALL RESIDENTS
OF SOUTHWESTERN CALIFORNIA SHOULD BE PREPARED FOR A VERY STRONG
STORM.
ON CHRISTMAS EVE (WEDNESDAY), THE AR WILL EXERT ITS GREATEST PUNCH
TO THE AREA WITH MODERATE TO HEAVY RAINFALL FOR ALL AREAS. THIS
FIRST WAVE WILL MOVE ACROSS THE AREA WEDNESDAY MORNING AND
AFTERNOON WITH PRECIPITATION TAPERING OFF WEDNESDAY EVENING. ON
THURSDAY, A SECONDARY AR PUNCH WILL IMPACT THE AREA WITH
IMPRESSIVE RAINFALL AMOUNTS (BUT LESS THAN WHAT FALLS ON
WEDNESDAY). ON FRIDAY, ALL MODELS AGREE ON A CONTINUED SHOWER
THREAT ACROSS THE AREA. HOWEVER ON SATURDAY, MODELS DIVERGE WITH
THE GFS INDICATING ANOTHER SHOT OF MODERATE RAINFALL WHILE THE
ECMWF JUST INDICATES SCATTERED SHOWERS. HOWEVER, WILL NOT GET
BOGGED DOWN IN THOSE DIFFERENCES AT THE DAY 7-8 TIME FRAME.
THROUGH SATURDAY EVENING, RAINFALL TOTALS WILL BE VERY
IMPRESSIVE. NORTH OF POINT CONCEPTION, 2-4 INCHES IS EXPECTED FOR
COASTS/VALLEYS WITH 4-8 INCHES ACROSS THE FOOTHILLS AND MOUNTAINS.
SOUTH OF POINT CONCEPTION, AMOUNTS WILL EVEN BE MORE IMPRESSIVE,
4-6 INCHES FOR COASTAL/VALLEY AREAS AND 6-12+ INCHES FOR THE
FOOTHILLS AND MOUNTAINS. RAINFALL RATES ALSO WILL BE PRETTY
IMPRESSIVE. PEAK HOURLY RATES OF 0.50-1.00 INCHES ARE LIKELY SOUTH
OF POINT CONCEPTION AND 0.30-0.80 INCHES NORTH OF POINT
CONCEPTION. GIVEN THE AMOUNT OF EXPECTED RAINFALL AND THE
ASSOCIATED RATES, SIGNIFICANT HYDROLOGIC ISSUES CAN BE EXPECTED,
INCLUDING WIDESPREAD URBAN FLOODING AND THE THREAT OF MUD AND
DEBRIS FLOWS.
AS FOR SNOW, GIVEN THE NATURE OF THIS SYSTEM, SNOW LEVELS WILL
REMAIN RATHER HIGH THROUGH THE BULK OF THE PRECIPITATION. SNOW
LEVELS WILL REMAIN ABOVE THE 7000 FEET THROUGH CHRISTMAS DAY, BUT
WILL DROP INTO THE 5500-6500 FOOT RANGE FRIDAY THROUGH SATURDAY.
SO, RESORT LEVELS WILL LIKELY RECEIVE SOME IMPRESSIVE SNOW TOTALS
WHEN ALL IS SAID AND DONE, BUT LOWER ELEVATIONS WILL NOT.
AVIATION
20/1804Z.
AROUND 17Z, THE MARINE LAYER DEPTH WAS NEAR 1500 FEET DEEP AT
KLAX. THE TOP OF THE MARINE INVERSION WAS AROUND 4500 FEET WITH A
TEMPERATURE NEAR 19 DEG C.
HIGH CONFIDENCE IN THE CURRENT FORECAST FOR DESERT TERMINALS.
ELSEWHERE, LOW TO MODERATE CONFIDENCE EXISTS IN THE COASTAL AND
VALLEY TERMINALS. PRIMARILY MVFR CONDS ARE EXPECTED THROUGH 19Z AT
LOS ANGELES COUNTY COASTAL TERMINALS AND LIFR TO IFR CONDS AT
KBUR, KVNY AND KCMA. CONDS SHOULD IMPROVE TO VFR AT THESE
AIRFIELDS BY 20Z OR 21Z. AN EARLY RETURN OF IFR TO MVFR CONDITIONS
SHOULD BE EXPECTED FOR THE COASTAL TERMINALS, THEN MOVING INTO
VALLEY TERMINALS OVERNIGHT AND LOWERING. SOME AIRFIELDS COULD SEE
LIFR CONDS LATE TONIGHT INTO SUN MORNING AS WELL. THE TIMING OF
FLIGHT CAT CHANGES MAY BE OFF +/- 1 TO 2 HOURS.
KLAX...LOW TO MODERATE CONFIDENCE IN THE 18Z TAF. MVFR CONDS ARE
EXPECTED THROUGH 19Z, THEN CONDITIONS SHOULD IMPROVE TO THE VFR
BEFORE LOWERING AGAIN TO MVFR AROUND 03Z. A RETURN OF IFR CONDS
IS EXPECTED AROUND 08Z THEN IMPROVING AFT 18Z SUN. THE TIMING OF
FLIGHT CAT CHANGES MAY BE OFF +/- 1 TO 2 HOURS.
KBUR...LOW TO MODERATE CONFIDENCE IN THE 18Z TAF. LIFR CONDS ARE
EXPECTED THROUGH 19Z. VFR CONDS SHOULD DEVELOP 19Z AND 20Z. IFR
CONDITIONS SHOULD RETURN AS SOON AS 05Z. THERE IS A 50% CHANCE VFR
CONDS WILL DEVELOP AROUND 15Z SUN, BUT THERE IS ALSO A 50% CHANCE
OF IFR CONDS THRU 18Z. THE TIMING OF FLIGHT CAT CHANGES MAY BE
OFF +/- 1 TO 2 HOURS.
MARINE
20/1126 AM.
HIGH CONFIDENCE IN THE CURRENT FORECAST THROUGH MONDAY NIGHT,
THEN MODERATE CONFIDENCE THEREAFTER. CONFIDENCE LOWER DUE TO
TIMING AND SEAS. WINDS AND SEAS WILL LARGELY REMAIN BELOW SCA
LEVELS THROUGH MONDAY NIGHT.
ON TUESDAY, WINDS AND SEAS WILL LIKELY RAPIDLY INCREASE TO
DANGEROUS LEVELS AS A STORM SYSTEM APPROACHES THE COASTAL WATERS.
THERE IS A 70-90 PERCENT CHANCE OF SCA LEVEL SOUTHERLY WINDS
DEVELOPING BY TUESDAY AFTERNOON WITH A LIKELY (60-70 PERCENT)
CHANCE OF WIDESPREAD GALE FORCE WINDS THROUGH TUESDAY NIGHT. LARGE
SHORT-PERIOD SEAS ARE LIKELY TO DEVELOP TUESDAY NIGHT AND SHOULD
LINGER WEDNESDAY INTO THURSDAY.
BOATERS ARE URGED TO MONITOR THE LATEST WEATHER FORECASTS. IF
MARINE WEATHER CONDITIONS DETERIORATE AS ADVERTISED, BOATERS
SHOULD REMAIN IN SAFE HARBOR DURING THIS SIGNIFICANT STORM.
UNPROTECTED SOUTH FACING HARBORS MAY BE ESPECIALLY VULNERABLE TO
THE SOUTH SWELL AND WINDS.
LOX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC...THOMPSON
AVIATION...SIRARD
MARINE...SIRARD
SYNOPSIS...30/CILIBERTI
WEATHER.GOV/LOSANGELES
EXPERIMENTAL GRAPHICAL HAZARDOUS WEATHER OUTLOOK AT:
HTTPS://WWW.WEATHER.GOV/ERH/GHWO?WFO=LOX
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