936
FXUS66 KSGX 211826
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
1126 AM PDT MON SEP 21 2026
SYNOPSIS
COOLER CONDITIONS TODAY WITH GRADUAL WARMING FOR THE MIDDLE OF THE
WEEK. MINIMAL CHANGE IN TEMPERATURES EXPECTED FOR THE END OF THE
WEEK INTO THE WEEKEND. A DEEP MARINE LAYER WILL BE MAINTAINED INTO
TUESDAY MORNING WITH NIGHT AND MORNING LOW CLOUDS SPREADING INTO THE
VALLEYS. THERE IS A A SLIGHT CHANCE OF SHOWERS AND ISOLATED
THUNDERSTORMS OVER THE MOUNTAINS THURSDAY AFTERNOON, WITH OTHERWISE
DRY CONDITIONS EXPECTED TO PREVAIL.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
LOW CLOUDS ARE HANGING ON THIS MORNING ACROSS THE COASTAL BASIN WITH
AREAS OF HIGH CLOUDS STREAMING TO THE NORTHEAST ACROSS THE AREA.
CLOUD COVERAGE COULD BE FAIRLY PERSISTENT TODAY FOR SOME AREAS AS
A CLOSED UPPER LEVEL LOW MOVE EAST ACROSS THE US WEST COAST.
THERE WERE A FEW SPRINKLES ACROSS THE COASTAL BASIN THIS MORNING
WITH CONTINUED PRECIPITATION TO OUR EAST IN THE DESERT SOUTHWEST,
BUT THERE IS LESS THAN 15 PERCENT CHANCE OF ACCUMULATING
PRECIPITATION THROUGH THE AFTERNOON. UNDER THE INFLUENCE OF THE
LOW, THE MARINE LAYER WILL STAY 3000 TO 3500 FT DEEP INTO TUESDAY
MORNING WITH LOW CLOUDS EXPECTED TO FILL IN MUCH OF THE COASTAL
BASIN OVERNIGHT.
HIGHS TODAY WILL BE A FEW TO AROUND 5 DEGREES COOLER THAN SUNDAY AND
AS MUCH AS 5 TO 10 DEGREES BELOW AVERAGE FOR THE VALLEYS. HIGH
TEMPERATURES ON TUESDAY WILL WARM A FEW TO AROUND 5 DEGREES WITH THE
GREATEST WARMING FOR THE INLAND VALLEYS. WARMING WILL CONTINUE ON
WEDNESDAY WITH HIGH TEMPERATURES AS MUCH AS ANOTHER 5 TO 10 DEGREES
WARMER FOR THE INLAND EMPIRE AND INLAND ORANGE COUNTY. WITH THE
WARMING, HIGH TEMPERATURES ON WEDNESDAY WILL BE WITHIN A FEW DEGREES
OF AVERAGE FOR MOST AREAS. ANOTHER FEW DEGREES OF WARMING IS
EXPECTED THURSDAY AND FRIDAY WITH TEMPERATURES ALONG THE COAST WITH
THE HIGHEST DEPARTURE FROM NORMAL AT 7 TO 12 DEGREES. FOR THE LATTER
HALF OF THE WEEK, OVERNIGHT LOWS WILL INCREASE TO THE MID-60S TO
70 WEST OF THE MOUNTAINS AND IN THE UPPER 70S TO LOW 80S IN THE
LOW DESERT.
FOR THURSDAY, A CLOSED LOW LINGERING TO OUR SOUTHWEST WILL START TO
MOVE EAST. THIS LOW WILL HAVE SOME UPPER LEVEL MOISTURE ENTRAINED IN
IT WHICH MAY BRING SOME PRECIPITATION TO THE AREA, MOST LIKELY FOR
THE MOUNTAINS. THE LOW WILL BRING SOME INCREASE IN INSTABILITY, SO A
SLIGHT CHANCE OF ISOLATED THUNDERSTORMS (15-20%) HAS BEEN INTRODUCED
TO THE FORECAST, MAINLY CONFINED TO THE MOUNTAINS. THERE IS LOW
CONFIDENCE IN ANY POTENTIAL IMPACTS, ESPECIALLY IN THE WAY OF
FLOODING. THE SPREAD IN NBM GUIDANCE BETWEEN 10TH PERCENTILE AND
90TH PERCENTILE FOR 24 HOUR RAINFALL IS 0 AND 0.55 INCHES
RESPECTIVELY.
TROPICAL CYCLONE POLO, OFF THE SOUTHWEST COAST OF MEXICO, IS
FORECAST BY THE NATIONAL HURRICANE CENTER TO BECOME A MAJOR
HURRICANE OVER THE NEW FEW DAYS WITH A TRACK EVENTUALLY AND
GENERALLY TOWARD THE WEST NORTHWEST WHICH MIGHT PUT THE CENTER A FEW
HUNDRED MILES SOUTH OF THE SOUTHERN TIP OF BAJA EARLY SATURDAY.
THERE REMAINS A LOT OF UNCERTAINTY IN THE FORECAST FOR LATE IN THE
WEEKEND INTO NEXT WEEK BUT THERE COULD EVENTUALLY BE AT LEAST SOME
PERIPHERAL IMPACTS TO PORTIONS OF SOUTHERN CALIFORNIA.
AVIATION
211800Z...COAST/VALLEYS...SCT-BKN LOW CLOUDS WITH BASES 2000-3500
FEET MSL STILL COVER MUCH OF THE COASTAL BASIN BUT CIGS ARE MOSTLY
ABOVE 3000 FT MSL. LOW CLOUDS WITH SIMILAR BASES WILL BEGIN TO
INCREASE IN COVERAGE AROUND 23Z, COVERING THE COASTAL BASIN BY 12Z
TUE. MOST CIGS ARE LIKELY TO BE ABOVE 2000 FT MSL.
ELSEWHERE...SCT CLOUDS AOA 15000 FEET MSL WITH UNRESTRICTED VIS
THROUGH TONIGHT.
MARINE
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH FRIDAY.
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...CO
AVIATION/MARINE...PG
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