242
FXUS66 KSGX 280932
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
232 AM PDT FRI AUG 28 2026
SYNOPSIS
HIGH PRESSURE REMAINS LOCKED IN PLACE IN THE NEAR TERM AS HOT DAYS
AND NEAR-RECORD WARM NIGHTS CONTINUE THROUGH FRIDAY NIGHT. SLIGHT
CHANCE OF SHOWERS AND THUNDERSTORMS FOR THE MOUNTAINS THIS AFTERNOON
AND FRIDAY AFTERNOON. HIGH PRESSURE WEAKENS AND SLIDES EAST THIS
WEEKEND WITH TEMPERATURES COOLING TO NEAR AVERAGE BY SUNDAY AND
BELOW AVERAGE BY EARLY NEXT WEEK. FOR TUESDAY AND WEDNESDAY OF NEXT
WEEK, INCREASED HIGH CLOUD COVER IS LIKELY ALONG WITH A 20 TO 30
PERCENT CHANCE OF PRECIPITATION FROM A TROPICAL SYSTEM THAT HAS
YET TO DEVELOP.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
..UPDATED AVIATION DISCUSSION
THE STRONG UPPER RIDGE CENTERED OVER ARIZONA WILL REMAIN IN PLACE
THROUGH FRIDAY WITH 500 MB HEIGHTS HOVERING AROUND 594 DM OVER
SOUTHERN CALIFORNIA. HIGH TEMPERATURES GENERALLY OVERPERFORMED
YESTERDAY WITH DAILY RECORD HIGH MAXIMUMS SET IN A FEW INLAND
VALLEY AND DESERT LOCATIONS. THIS OVERPERFORMING TREND WILL HAVE
TO COMPETE WITH INCREASED CLOUD COVER TODAY, COURTESY OF THE
REMNANTS OF TROPICAL STORM ISELLE, SO FORECAST HIGHS ARE FEW
DEGREES LOWER THAN YESTERDAY'S TEMPS. REGARDLESS OF EXACT
TEMPERATURES, HOT DAYS IN COMBINATION WITH NEAR-RECORD WARM NIGHTS
WILL PRODUCE MAJOR TO LOCALLY EXTREME HEATRISK THROUGH FRIDAY FOR
INLAND VALLEYS AND LOWER DESERTS. MODERATE TO LOCALLY MAJOR
HEATRISK IS EXPECTED FOR THE MOUNTAINS, HIGH DESERT, AND AREAS
NEAR THE COAST.
THERE IS A SLIGHT CHANCE (10-20%) FOR THUNDERSTORMS OVER THE
MOUNTAINS THIS AFTERNOON AND FRIDAY AFTERNOON. THERE IS AMPLE
MOISTURE PRESENT (PWATS AROUND 1.4-1.5"), BUT THE 12Z KNKX SOUNDING
INDICATES THE PRESENCE OF SUBSTANTIAL MID-LEVEL CAPPING, WHICH
WILL KEEP CONVECTION QUITE LIMITED.
BY SATURDAY, THE RIDGE BEGINS TO WEAKEN AND SLIDE EASTWARD AS A
ROBUST UPPER TROUGH PUSHES INTO THE PNW. THIS WILL USHER IN A
WELCOME COOLING TREND ACROSS THE REGION. TEMPERATURES ARE
EXPECTED TO RETURN TO NEAR AVERAGE BY SUNDAY WITH HIGHS FURTHER
COOLING TO AROUND 3 TO 7 DEGREES BELOW AVERAGE EARLY NEXT WEEK.
THIS PATTERN CHANGE WILL ALSO PRODUCE BREEZY WESTERLY WINDS FOR
THE MOUNTAINS AND DESERTS AND DEEPEN THE MARINE LAYER FOR SUNDAY
AND MONDAY.
FROM NEXT TUESDAY ONWARD, THE FORECAST BECOMES MORE UNCERTAIN.
THE SYNOPTIC SET UP WILL REMAIN GENERALLY UNCHANGED ON THE
SYNOPTIC SCALE WITH TROUGHING OVER THE PNW AND RIDGING OVER THE
SOUTH-CENTRAL CONUS RESULTING IN SOUTHWESTERLY FLOW THE REGION.
SIMULTANEOUSLY, GLOBAL MODELS INDICATE THAT A TROPICAL SYSTEM
WILL PASS WELL TO THE SOUTHWEST EARLY NEXT WEEK. THE EXACT
EVOLUTION OF THIS LARGE SCALE SET UP AND THE TRACK OF THE TROPICAL
SYSTEM WILL DETERMINE HOW MUCH MOISTURE WILL BE DRAWN INTO THIS
REGION FOR THE MIDDLE OF NEXT WEEK. MOST ENSEMBLES INDICATE A
NOTABLE INCREASE IN PWATS OVER SOUTHERN CALIFORNIA NEXT WEEK, BUT
ONLY ABOUT 20-30% HAVE ANY PRECIPITATION AT THIS TIME.
AVIATION
280930Z...COAST...LOW CLOUDS BASED 400-700 FT MSL WILL CONTINUE TO
BECOME MORE WIDESPREAD THROUGH COASTAL SD COUNTY, AS MID TO UPPER
LEVEL CLOUDS MOVE NORTHWARDS OUT OF THE AREA, THOUGH LIKELY WILL
REMAIN PATCHY FOR MOST OF THE NIGHT. BEST CHANCES FOR IMPACTS FOR
COASTAL SITES IS THROUGH 15Z, WITH VIS RESTRICTIONS 2-5 SM OVER
HIGHER COASTAL TERRAIN. LOW CLOUDS EXPECTED TO CLEAR BY 16Z, WITH
LOW CLOUDS OF SIMILAR BASES/PATCHINESS FORMING AFTER 09Z SAT.
MOUNTAINS/DESERTS...CUMULUS BASED AROUND 9,000FT MSL OVER THE
MOUNTAINS TODAY 20Z TO SAT 01Z WITH ISOLATED CB CLOUD TOPS RISING TO
40,000FT MSL. THERE IS A 10-15% CHANCE OF ISO TSRA/SHRA OVER THE
MOUNTAINS AND A 5-10% CHANCE IN THE DESERTS UNTIL 01Z SAT. ANY TS
THAT DEVELOPS COULD PRODUCE GUSTY, ERRATIC WINDS.
REGIONWIDE...HIGH CLOUDS AOA 15,000FT MSL WILL CONTINUE THIS
MORNING AND AFTERNOON, DECREASING THROUGH THIS EVENING.
MARINE
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH TUESDAY.
BEACHES
A FRESH 3 FOOT SWELL FROM THE SOUTH-SOUTHWEST (200 DEGREES) AT 15-17
SECONDS MOVES INTO THE REGION SATURDAY-SUNDAY. THIS WILL BRING
LOCALIZED ELEVATED SURF OF 4-6 FEET TO SOUTHWEST-FACING BEACHES,
MOSTLY IN NORTH SAN DIEGO COUNTY AND ORANGE COUNTY.
SGX WATCHES/WARNINGS/ADVISORIES
CA...HEAT ADVISORY UNTIL 8 PM PDT THIS EVENING FOR ORANGE COUNTY
COASTAL AREAS-RIVERSIDE COUNTY MOUNTAINS-SAN BERNARDINO
COUNTY MOUNTAINS-SAN DIEGO COUNTY COASTAL AREAS.
EXTREME HEAT WARNING UNTIL 8 PM PDT THIS EVENING FOR APPLE AND
LUCERNE VALLEYS-COACHELLA VALLEY-ORANGE COUNTY INLAND AREAS-
SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE INLAND
EMPIRE-SAN DIEGO COUNTY DESERTS-SAN DIEGO COUNTY MOUNTAINS-
SAN DIEGO COUNTY VALLEYS-SAN GORGONIO PASS NEAR BANNING-
SANTA ANA MOUNTAINS AND FOOTHILLS.
PZ...NONE.
PUBLIC...SS
AVIATION/MARINE/BEACHES...CSP
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