539
FXUS66 KSGX 182124
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
124 PM PST THU DEC 18 2025
SYNOPSIS
WARM AND DRY WEATHER WILL CONTINUE ACROSS THE REGION THROUGH THE
UPCOMING WEEKEND. NIGHT AND MORNING LOW CLOUDS AND FOG WILL
PERSIST ON FRIDAY, WITH LESS FOG FOR LOWER ELEVATIONS NEAR THE
COAST BY THE WEEKEND INTO EARLY NEXT WEEK. A LOW PRESSURE SYSTEM
WILL BRING LIGHT SHOWERS BEGINNING TUESDAY, EVOLVING INTO HEAVIER
RAINFALL ACROSS ALL AREAS BY WEDNESDAY. THE ACTIVE WEATHER PATTERN
LOOKS TO CONTINUE WITH ELEVATED RAIN CHANCES CONTINUING INTO THE
END OF NEXT WEEK.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
..PREVIOUS DISCUSSION (1057 AM THURSDAY)
HIGH TEMPERATURES FOR TODAY WILL BE MUCH WARMER FOR THE COAST AND
AND VALLEYS THAN YESTERDAY, WITH HIGHS 10 TO AS MUCH AS 25
DEGREES ABOVE NORMAL. HIGH TEMPERATURES FOR TODAY WILL RANGE FROM
AROUND 70 NEAR THE COAST TO THE UPPER 70S TO MID 80S FOR THE
VALLEYS AND FOR THE LOWER DESERTS. HIGH TEMPERATURE RECORDS FOR
TODAY ARE MOST LIKELY TO BE TIED OR BROKEN IN THE MOUNTAINS,
INLAND VALLEYS, AND LOWER DESERTS. SOME LOCATIONS THAT MAY BREAK
RECORDS INCLUDE CAMPO, ALPINE, BIG BEAR AND IDYLLWILD.
THE AREA OF HIGH PRESSURE WILL BEGIN TO BREAK DOWN AND FLATTEN
OVER MEXICO AS A TROUGH PUSHES SOUTHWARD FROM THE GULF OF ALASKA
INTO THE PACIFIC NORTHWEST BY EARLY NEXT WEEK. THIS WILL LEAD TO
GREATER ONSHORE FLOW AND A SUBTLE COOLING TREND BY THE WEEKEND
INTO MONDAY, THOUGH TEMPERATURES WILL STILL BE AROUND 5 TO 15
DEGREES ABOVE NORMAL. THIS WILL ALSO HELP THE MARINE LAYER DEEPEN,
LEADING TO FOGGY CONDITIONS TO REMAIN IN MORE ELEVATED TERRAIN
AWAY FROM THE COAST EACH MORNING.
A MOISTURE PLUME/ATMOSPHERIC RIVER ("PINEAPPLE EXPRESS")
CURRENTLY FROM HAWAII CONTINUES TO PUMP MOISTURE INTO THE PACIFIC
NORTHWEST. THIS SYSTEM, ALONG WITH THE AFOREMENTIONED TROUGH TO
THE NORTH, WILL COMBINE AND PUSH THIS ATMOSPHERIC RIVER SOUTHWARD
INTO OUR REGION BY TUESDAY THROUGH THE CHRISTMAS HOLIDAY. TIMING
STILL REMAINS FAIRLY UNCERTAIN ON WHEN THIS MAY OCCUR AS THE
TROUGH OF LOW PRESSURE MAY ELONGATE OVER THE OCEAN, DELAYING THE
RAIN'S ONSET. THE MOST LIKELY SCENARIO IS TO SEE SOME LIGHT
SHOWERS DEVELOPING OUT AHEAD OF THE STORM SYSTEM SOMETIME ON
TUESDAY. MODELS SUGGEST WEDNESDAY AS THE PERIOD OF THE HEAVIEST
RAIN AS THE ATMOSPHERIC RIVER MOVES THROUGH THE AREA FROM NORTH TO
SOUTH, WITH ADDITIONAL LIGHTER SHOWERS EXPECTED ON CHRISTMAS DAY.
RAINFALL AMOUNTS ARE STILL UNCERTAIN BUT AREAS OF THE MOUNTAINS
HAVE A 70%+ OF SEEING 2 INCHES OF RAINFALL OR MORE DURING THIS
PERIOD. THESE CHANCES RANGE FROM 25-45% ACROSS THE INLAND EMPIRE
AND WESTERN SAN DIEGO COUNTY, TO NEAR 65% CHANCE IN ORANGE COUNTY.
THE DESERTS ALSO LOOK TO RECEIVE RAIN FROM THIS WITH A 25-35%
CHANCE OF 1 INCH OR MORE IN THE LOWER DESERTS, SLIGHTLY HIGHER
CHANCES IN THE HIGH DESERT. THIS WILL LEAD TO AN INCREASED DEBRIS
FLOW AND FLOODING RISK ACROSS ALL AREAS. CONFIDENCE CONTINUES TO
INCREASE THAT SNOW LEVELS WILL BE HIGH, MAINLY ABOVE 8,000 FEET
FOR THE FIRST PART OF THE STORM SYSTEM THROUGH TUESDAY THROUGH
EARLY THURSDAY. PLEASE PLAN ACCORDINGLY IF YOU WILL BE TRAVELING
FOR THE CHRISTMAS HOLIDAY AS TRAVEL IMPACTS ARE LIKELY.
ENSEMBLE MODELS CONTINUE TO SHOW AN ACTIVE WEATHER PATTERN
CONTINUING INTO LATER NEXT WEEK. THE LOW PRESSURE SYSTEM THAT WILL
BRING THE RAIN AROUND CHRISTMAS MAY STICK AROUND FURTHER INTO
NEXT WEEK, BRINGING ADDITIONAL PERIODS OF RAINFALL AND HIGH
ELEVATION SNOW. A LOT OF THIS WILL DEPEND ON THE EXACT TRACK OF
THE LOW PRESSURE SYSTEM AND HOW COLD IT BECOMES. IF THE LOW MOVES
SLOWER AND REMAINS OFF THE COAST, ADDITIONAL PERIODS OF HEAVY
PRECIP MAY OCCUR INTO NEXT WEEKEND. IF THE LOW MOVES FASTER, WE
MAY SEE A PERIOD OF DRIER WEATHER THE DAYS FOLLOWING THE CHRISTMAS
HOLIDAY.
AVIATION
182000Z...COAST...PATCHY LOW CLOUDS AND FOG LINGERING AT THE COAST
THIS AFTERNOON BUT IMPACTS AT COASTAL TAF SITES ARE UNLIKELY. LOW
CLOUDS AND FOG REDEVELOPING ALONG THE COAST AFTER 01Z FRI, NOT
EXTENDING MORE THAN 5 MILES INLAND BY FRI MORNING. THERE WILL BE
ABOUT A 50-60 PERCENT CHANCE FOR CIG AND VIS IMPACTS AT COASTAL TAF
SITES BETWEEN 06Z AND 17Z FRI...WITH CLOUD BASES 002-005 FT MSL AND
VIS 1-5SM. PERIODS OF VIS BLO 1SM POSSIBLE 10Z-16Z FRI.
OTHERWISE...SCT-BKN HIGH CLOUDS WITH UNRESTRICTED VIS THROUGH
TONIGHT.
MARINE
PATCHY FOG COULD REDUCE VISIBILITY TO 1 SM LATE TONIGHT INTO FRIDAY
MORNING. OTHERWISE, NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED
THROUGH TUESDAY.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC...APR
AVIATION/MARINE...PG
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