489
FXUS66 KSGX 272028
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
128 PM PDT THU AUG 27 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...
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
271800Z...COAST...LOW CLOUDS THIS MORNING HAVE LARGELY CLEARED OUT,
BUT REMAIN RIGHT ALONG THE IMMEDIATE COAST OF EXTREME SOUTHWESTERN
SAN DIEGO COUNTY. THESE CLOUDS ARE GENERALLY BASED AROUND 500FT MSL
AND WITHIN SOUTH-SOUTHWESTERLY FLOW, WILL LINGER IN THE VICINITY OF
KSAN INTO THE AFTERNOON. GUIDANCE SUGGESTS MARINE LAYER CLOUDS WILL
BE EVEN PATCHIER TONIGHT THAN THIS MORNING, WITH ONLY STRAY PATCHES
OFF THE NORTHERN SD/ORANGE COUNTY COASTS. BEST CHANCES FOR CIGS
OVERNIGHT REMAIN ACROSS THE SOUTHERN SAN DIEGO COUNTY COASTS, WITH
KSAN HAVING A ~70% CHANCE FOR CIGS BETWEEN 11-15Z FRIDAY, WITH A
~40% CHANCE AT KCRQ. BASES FOR ANY CLOUDS WOULD BE AROUND 500FT WITH
VIS RESTRICTIONS TO 3-6 SM IN BR. ANY CLOUDS THAT DO PUSH ONSHORE
WILL CLEAR BACK OUT OFFSHORE BY 16Z.
MOUNTAINS/DESERTS...CUMULUS BASED AROUND 9000 FEET MSL OVER THE
MOUNTAINS THIS AFTERNOON WITH ISOLATED CB CLOUD TOPS RISING TO 40000
FEET MSL. THERE IS A 15-20% CHANCE OF TSRA OVER THE MOUNTAINS AND A
5-15% CHANCE IN THE DESERTS UNTIL 01Z. ANY TS THAT DEVELOPS COULD
PRODUCE GUSTY, ERRATIC WINDS.
REGIONWIDE...HIGH CLOUDS AOA 15000 FEET MSL WILL CONTINUE TODAY AND
TONIGHT, DECREASING EARLY FRIDAY.
MARINE
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH MONDAY.
BEACHES
A 4-FOOT SOUTHERLY SWELL (FROM 170 DEGREES) AT 12-13 SECONDS WILL
CONTINUE TO PRODUCE ELEVATED SURF THROUGH TONIGHT, PARTICULARLY FOR
SOUTH-FACING BEACHES OF ORANGE COUNTY AND NORTHERN SAN DIEGO COUNTY.
SURF OF 3 TO 5 FEET, WITH SETS UP TO 7 FEET IS EXPECTED. SEE THE
COASTAL HAZARD MESSAGE FOR DETAILS ON BEACH HAZARDS.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...BEACH HAZARDS STATEMENT UNTIL 11 PM PDT THIS EVENING FOR ORANGE
COUNTY COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS.
HEAT ADVISORY UNTIL 8 PM PDT FRIDAY FOR ORANGE COUNTY COASTAL
AREAS-RIVERSIDE COUNTY MOUNTAINS-SAN BERNARDINO COUNTY
MOUNTAINS-SAN DIEGO COUNTY COASTAL AREAS.
EXTREME HEAT WARNING UNTIL 8 PM PDT FRIDAY 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/FIRE WEATHER...KW
AVIATION/MARINE...MUNYAN
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