238
FXUS66 KSGX 201812
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
1112 AM PDT SUN SEP 20 2026
SYNOPSIS
TEMPERATURES REMAIN BELOW NORMAL UNTIL WEDNESDAY WITH A DEEP
MARINE LAYER AND PERHAPS MORNING DRIZZLE EARLY WEEK. WARMER
WEATHER RETURNS FOR THE END OF NEXT WEEK AS HIGH PRESSURE BUILDS.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
..UPDATED AVIATION DISCUSSION
THE 00Z SOUNDING SATURDAY AFTERNOON SHOWS A WELL MIXED MARINE
BOUNDARY LAYER, AROUND 2500 FEET DEEP WITH AN INVERSION UP TO 5,000
FEET AND VERY DRY AIR WITHIN AND ABOVE IT. PATCHY LOW CLOUDS ARE
EXPECTED TO FILL OVER THE LOWLANDS OF SAN DIEGO AND ORANGE COUNTIES
AS WELL AS PARTS OF THE INLAND EMPIRE THROUGH THIS MORNING. THE
CLOSED UPPER LOW CONTINUES TO APPROACH OUR REGION THROUGH MONDAY,
DEEPENING THE MARINE LAYER TO ABOUT 4000-5000 FEET TONIGHT INTO
EARLY MONDAY AND SIGNIFICANTLY IMPROVING MINIMUM HUMIDITIES MONDAY
AFTERNOON ACROSS MOUNTAINS (12-25% THIS AFTERNOON TO 25-50%
MONDAY) AND DESERTS (10-15% THIS AFTERNOON TO 18-30% MONDAY). WITH
THE DEEPENING MARINE LAYER, THERE IS A MODERATE CHANCE FOR
DRIZZLE IN THE COASTAL BASIN EARLY MONDAY AND EARLY TUESDAY.
MONDAY WILL ALSO LIKELY BE THE COOLEST AND BREEZIEST DAY OF THE
WEEK AS THE MAIN TROUGH AXIS PASSES THROUGH THE REGION. W/SW
WINDS WILL BE SLIGHTLY ELEVATED MONDAY AFTERNOON AND EVENING OVER
DESERT SLOPES, GUSTING 20-35 MPH AND HIGHER THROUGH THE BANNING
PASS. TEMPERATURES WILL LIKELY STRUGGLE TO REACH THE 80S ACROSS
THE COASTAL BASIN WITH PERHAPS A FEW LOW-80S IN THE IE WHILE LOW
DESERT TEMPERATURES ARE LIKELY (80% CHANCE) TO REMAIN BELOW 100F
BOTH MONDAY AND TUESDAY.
AS THE CLOSED LOW DEPARTS THE REGION, THE LONGWAVE BACKGROUND RIDGE
ACROSS THE SOUTHERN US REPLACES THE LOW AND FILLS IN OVER SOCAL,
IMMEDIATELY SPIKING THE TEMPERATURES BACK TO NEAR AVERAGE FOR
INLAND AREAS FOR WEDNESDAY, A JUMP OF NEARLY 8-12F. THAT
CORRESPONDS TO HIGHS WITHIN A FEW DEGREES OF 80 AT THE COAST,
UPPER 80S INLAND, MID-90S IN THE IE AND LOW-100S IN THE LOWER
DESERTS WEDNESDAY THROUGH FRIDAY.
AT THIS TIME, BOTH THE ECMWF AND GFS ARE IN AGREEMENT THAT A TROUGH
WILL MOVE THROUGH NORCAL AND THE PNW NEXT WEEKEND, THOUGH IT
REMAINS UNCERTAIN HOW MUCH IT WILL HAVE AN INFLUENCE ON
TEMPERATURES IN SOCAL.
AVIATION
201800Z...COAST/VALLEYS...PARTIALLY MASKED ON SATELLITE BY SCT-BKN
HIGH CLOUDS, LOWER MARINE LAYER CLOUDS (BASED NEAR 2500FT MSL) THAT
SPREAD WELL INLAND OVERNIGHT HAVE BEGUN TO ERODE ACROSS THE INLAND
VALLEYS. UNDER THE INFLUENCE OF A LARGER STORM SYSTEM SPREADING INTO
CALIFORNIA, SCT MARINE LAYER CLOUDS LOOK TO REMAIN PRESENT ALONG THE
COASTS INTO THE AFTERNOON. INTERMITTENT BKN CIGS REMAIN POSSIBLE
INTO THE AFTERNOON. COME 00Z MONDAY, EXPECTING THESE LOW CLOUDS TO
REDEVELOP AND SURGE BACK INLAND, FILLING THE ENTIRE COASTAL BASIN BY
09Z. BASES WILL GENERALLY LIFT TO AROUND 2500-3000FT MSL, BUT COULD
LIFT ABOVE 3000FT OVERNIGHT. CLOUDS BEGIN TO SCATTER AROUND 16-18Z,
BUT COULD TAKE UNTIL AS LATE AS 21Z MONDAY TO FULLY CLEAR OUT.
MOUNTAINS/DESERTS...VFR CONDITIONS PREVAIL INTO MONDAY. BKN HIGH
CLOUDS AOA 20000 FT MSL BECOMING SCT TO FEW IN THE AFTERNOON AND
OVERNIGHT.
MARINE
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH FRIDAY.
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC...WESTERINK
AVIATION/MARINE...MUNYAN
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