265
FXUS66 KSGX 171214
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
414 AM PST WED DEC 17 2025
SYNOPSIS
AREAS OF LOW CLOUDS AND LOCALLY DENSE FOG WILL CONTINUE FOR
COASTAL AREAS INTO THIS MORNING. ONSHORE FLOW WILL STRENGTHEN
FOR THIS AFTERNOON AND EVENING WITH WEST TO NORTHWEST WINDS FOR
THE SAN BERNARDINO COUNTY MOUNTAINS AND DESERTS GUSTING TO 35 TO
45 MPH. FOR THURSDAY, STRONGER HIGH PRESSURE ALOFT WILL BRING
WARMING OF 4 TO 8 DEGREES FOR THE COAST AND VALLEYS WITH HIGH
TEMPERATURES FOR THE INLAND VALLEYS AND LOWER COASTAL SLOPES OF
THE MOUNTAINS AROUND 20 DEGREES ABOVE AVERAGE. ONSHORE FLOW WILL
SPREAD COOLING INLAND FOR FRIDAY AND SATURDAY WITH NOT MUCH
CHANGE FOR SUNDAY AND MONDAY. AN APPROACHING LOW PRESSURE SYSTEM
FROM THE WEST WILL BRING INCREASING CHANCES FOR PRECIPITATION
BEGINNING TUESDAY WITH THE GREATEST CHANCES FOR HEAVIER
PRECIPITATION FOR CHRISTMAS EVE AND CHRISTMAS.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
SHORT TERM (TODAY THROUGH FRIDAY)
A STRONG SHALLOW MARINE INVERSION REMAINS IN PLACE ACROSS SOUTHERN
CALIFORNIA COASTAL AREAS EARLY THIS MORNING WITH SATELLITE
IMAGERY AND SURFACE REPORTS SHOWING WIDESPREAD LOW CLOUDS AND
LOCALLY DENSE FOG OVER THE COASTAL WATERS AND COASTAL AREAS WITH
THE LOWEST VISIBILITIES NEAR HIGHER COASTAL TERRAIN INTO THE FAR
WESTERN VALLEYS. LESS COVERAGE OF LOW CLOUDS IS EXPECTED FOR THE
FOLLOWING TWO NIGHTS WITH A GREATER RETURN FOR THE WEEKEND.
ONSHORE FLOW WILL STRENGTHEN FOR THIS AFTERNOON AND EVENING WITH
WEST TO NORTHWEST WINDS FOR THE SAN BERNARDINO COUNTY MOUNTAINS
AND DESERTS GUSTING TO 35 TO 45 MPH. HIGH TEMPERATURES TODAY FOR
MOST AREAS WILL BE WITHIN A FEW DEGREES OF THOSE ON TUESDAY WITH
THE COAST AND VALLEYS AROUND 4 TO 8 DEGREES WARMER ON THURSDAY AS
HIGH PRESSURE ALOFT STRENGTHENS. SEVERAL DAILY HIGH TEMPERATURE
RECORDS COULD BE TIED OR BROKEN ON THURSDAY, MAINLY FOR MOUNTAINS,
INLAND VALLEYS, AND LOWER DESERTS AND WELL AS SEVERAL RECORD WARM
LOW TEMPERATURES FOR EARLY FRIDAY.
WEAK ONSHORE FLOW WILL BEGIN TO SPREAD COOLING INLAND ON FRIDAY.
HIGH TEMPERATURES ON THURSDAY WILL BE AROUND 20 DEGREES ABOVE
AVERAGE FOR THE INLAND VALLEYS AND LOWER COASTAL SLOPES OF THE
MOUNTAINS WITH HIGH TEMPERATURES RANGING FROM THE LOWER TO MID 70S
FOR THE COAST TO THE LOWER TO MID 80S FOR THE VALLEYS AND FOR THE
LOWER DESERTS.
LONG TERM (SATURDAY THROUGH TUESDAY)
ONSHORE FLOW WILL CONTINUE TO SPREAD COOLING INLAND ON SATURDAY
WITH HIGH TEMPERATURES A FEW TO AROUND 5 DEGREES COOLER THAN
FRIDAY, BUT WITH HIGH TEMPERATURES STILL AS MUCH AS 15 TO 20
DEGREES ABOVE AVERAGE FOR THE HIGH DESERT. HIGH TEMPERATURES ON
SATURDAY WILL RANGE FROM THE MID TO UPPER 60S NEAR THE COAST TO
THE 70S FOR THE INLAND EMPIRE WITH THE LOWER DESERTS IN THE UPPER
70S TO MID 80S. NOT MUCH CHANGE IS EXPECTED FOR SUNDAY AND MONDAY.
NIGHT AND MORNING COASTAL LOW CLOUDS WILL SPREAD INLAND TO THE
FAR WESTERN VALLEYS AT TIMES WITH INCREASING MID AND HIGH CLOUDS
ACROSS SOUTHERN CALIFORNIA BY SUNDAY AND MONDAY.
FOR THE MIDDLE AND LATTER PART OF NEXT WEEK, A LOW PRESSURE
SYSTEM FROM THE WEST WITH A FEED OF SUBTROPICAL MOISTURE WILL
BRING INCREASING CHANCES FOR PRECIPITATION WITH THE GREATEST
CHANCES FOR LOCALLY HEAVY PRECIPITATION ON WEDNESDAY AND THURSDAY,
CHRISTMAS EVE INTO CHRISTMAS. FOR LYTLE CREEK, ONE OF THE
TYPICALLY WETTER LOCATIONS ON THE COASTAL SLOPES OF THE SAN
GABRIEL MOUNTAINS JUST TO THE WEST OF THE CAJON PASS, THE
DETERMINISTIC NBM HAS AROUND 6.5 INCHES OF RAINFALL FOR TUESDAY
THROUGH THURSDAY WITH THE CHANCE FOR ONE INCH OR MORE OF RAINFALL
FOR WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT OF 50 PERCENT WITH A
2 PERCENT CHANCE FOR 6 INCHES OR MORE. THE DETERMINISTIC NBM HAS
SNOW LEVELS OF 7000 FEET OR HIGHER FOR WEDNESDAY AND THURSDAY.
AVIATION
171030Z...COAST/WESTERN VALLEYS...LOW CLOUDS BASED 100-300 FEET MSL,
TOPS TO 900 FEET, AND FOG WITH VIS 0-3SM WILL CONTINUE THIS MORNING.
FOG WILL LIFT AND CLEAR 16-20Z, LAST AROUND KSNA. PATCHY SCT-BKN
CLOUDS AND VIS 4-6SM IN HZ TO LINGER AT THE IMMEDIATE COAST
THROUGHOUT THE DAY. LOW CLOUDS AND FOG RETURN 00-02Z WITH SIMILAR
BASES AND VIS, BUT THEN BECOME PATCHIER WITH REDUCED COVERAGE
OVERNIGHT INTO THURSDAY.
OTHERWISE...VFR CONDITIONS TODAY AND TONIGHT. SCT-BKN HIGH CLOUDS
THROUGH 17Z, THEN MOSTLY CLEAR.
MARINE
AREAS OF FOG WITH VERY LOW VISIBILITY WILL CONTINUE THIS MORNING. A
MARINE WEATHER STATEMENT CONTAINS MORE DETAILS. OTHERWISE, NO
ADDITIONAL HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH SUNDAY.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...DENSE FOG ADVISORY UNTIL 10 AM PST THIS MORNING FOR ORANGE
COUNTY COASTAL AREAS-ORANGE COUNTY INLAND AREAS-SAN DIEGO
COUNTY COASTAL AREAS.
PZ...NONE.
PUBLIC...17
AVIATION/MARINE...MM
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