359
FXUS66 KSGX 181627
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
927 AM PDT SUN MAY 18 2025
SYNOPSIS
WARMING CONDITIONS THIS WEEK WITH THE PEAK OF THE HEAT EXPECTED
TO BE WEDNESDAY CLOSER TO THE COAST AND THURSDAY FOR AREAS FURTHER
INLAND. PERIODS OF OFFSHORE WINDS ARE EXPECTED IN THE NIGHTS AND
EARLY MORNINGS, STRONGEST MONDAY AND WEAKENING INTO THE MIDDLE OF
THE WEEK. THE MARINE LAYER WILL BECOME MUCH SHALLOWER THIS WEEK
WITH PATCHIER COVERAGE NEAR THE COAST. BRIEF COOLING OVER THE
UPCOMING WEEKEND IS POSSIBLE.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
VISIBLE SATELLITE AT 9 AM WAS SHOWING MOSTLY CLOUDY CONDITIONS
ACROSS THE COASTAL BASIN. COASTAL AREAS SHOULD CLEAR WELL TODAY,
WITH AREAS OF CLOUDS LIKELY TO LINGER IN THE VALLEYS INTO THE
AFTERNOON. AREAS OF RAIN SHOWERS/DRIZZLE HAVE MOSTLY DIMINISHED,
ALTHOUGH A FEW ISOLATED SHOWERS MAY LINGER FOR THE NEXT FEW HOURS.
A 24 HOUR RAINFALL SUMMARY CAN BE FOUND ON WEATHER.GOV/SANDIEGO.
WINDS HAVE WEAKENED AND BECOME MORE LOCALIZED TO WIND PRONE
LOCATIONS. AN ENHANCED SEA BREEZE CAN BE EXPECTED TODAY WITH GUSTS
THIS AFTERNOON IN THE 30 TO 40 MPH RANGE ON THE DESERT MOUNTAIN
SLOPES INTO THE DESERTS, LOCALLY CLOSER TO 50 MPH THROUGH WIND
PRONE PASSES.
AS THE UPPER LEVEL LOW MOVES INTO THE ROCKY MOUNTAIN REGION THE
PRESSURE GRADIENT WILL TURN WEAKLY OFFSHORE, GENERATING A PERIOD OF
ENHANCED NORTHERLY WINDS MONDAY MORNING AND AFTERNOON. WIND GUSTS UP
TO 35 MPH CAN BE EXPECTED ON THE COASTAL SLOPES OF THE SAN
BERNARDINO AND SANTA ANA MOUNTAINS AS WELL AS BELOW THE CAJON
PASS, LOCALLY INTO THE INLAND EMPIRE. WEAKER OFFSHORE WINDS
EXPECTED EACH NIGHT AND MORNING THIS WEEK. A WEAK RIDGE OF HIGH
PRESSURE ALOFT WILL BUILD OVER THE US WEST COAST. DUE TO THE
PERIOD OF OFFSHORE WINDS EARLY IN THE WEEK AND BUILDING HEIGHTS
ALOFT, THE MARINE LAYER IS EXPECTED TO BECOME MUCH SHALLOWER THIS
WEEK WITH PATCHY COVERAGE ALONG THE COAST.
LATEST ENSEMBLE GUIDANCE IS INDICATING THE BUILDING RIDGE OF HIGH
PRESSURE WILL BE LESS AMPLIFIED THAN PREVIOUSLY SHOWN. THE WARMING
TREND IS STILL ON TRACK WITH THE PEAK WEDNESDAY AND THURSDAY, BUT
HIGH TEMPERATURES MAY BE LOWER THAN PREVIOUSLY THOUGHT. THAT BEING
SAID, HIGH TEMPERATURES ALONG THE COAST AND IN THE DESERTS ARE STILL
EXPECTED TO BE UP TO 10 DEGREES ABOVE AVERAGE WITH TEMPERATURES 10
TO 20 DEGREES ABOVE AVERAGE FOR THE VALLEYS. NBM CHANCES FOR
EXCEEDING 100 DEGREES IN THE INLAND EMPIRE WEDNESDAY AND THURSDAY
ARE 20 TO 30 PERCENT WITH A 10 PERCENT CHANCE IN THE SAN DIEGO
COUNTY VALLEYS. FOR INLAND ORANGE COUNTY CHANCES OF EXCEEDING 95
DEGREES ARE LESS THAN 10 PERCENT. EVEN THE 99TH PERCENTILE OF THE
ECMWF (ONLY ONE PERCENT OF ENSEMBLE MEMBERS WILL EXCEED THE LISTED
TEMPERATURE) KEEP HIGH TEMPERATURES WEST OF THE MOUNTAINS UNDER 100
DEGREES, ALTHOUGH IT DOES HAVE LOCATIONS LIKE RIVERSIDE REACHING THE
UPPER 90S. FOR THE LOW DESERT, CHANCES OF EXCEEDING 110 DEGREES HAVE
DECREASED, WITH CHANCES FOR WEDNESDAY NEAR ZERO AND CHANCES FOR
THURSDAY NEAR 25 PERCENT. HEATRISK FOR THE VALLEYS IS STILL EXPECTED
TO BE MODERATE, WITH LOCALLY MAJOR HEATRISK IN THE LOW DESERT. THIS
IS LIKELY DUE TO ELEVATED LOW TEMPERATURES, WHICH WILL LIMIT
OVERNIGHT RELIEF FROM THE HEAT.
BY FRIDAY, ENSEMBLE SOLUTIONS BEGIN TO SHOW AN UPPER LEVEL LOW
PRESSURE SYSTEM MOVING INTO THE PACIFIC NORTHWEST. THERE REMAINS
UNCERTAINTY IN HOW FAR SOUTH THIS TROUGH WILL DIG OVER THE WEEKEND
BUT THERE IS GOOD AGREEMENT IN IT WEAKENING THE RIDGE. HOW MUCH THE
RIDGE WEAKENS WILL HAVE AN INFLUENCE ON HOW MUCH COOLING WE'LL SEE,
HOW WELL THE MARINE LAYER WILL REBOUND, AND IF THERE WILL BE ANY
INCREASE IN WINDS FOR THE MOUNTAINS AND DESERTS. CURRENT FORECAST
FOR NEXT WEEKEND FOLLOWS THE NBM WITH A GRADUAL COOLING (BUT
TEMPERATURES REMAINING SLIGHTLY ABOVE NORMAL) AND INCREASED CLOUD
COVERAGE ALONG THE COAST.
AVIATION
181530Z...COAST/VALLEYS...SCT-OVC MARINE LAYER CLOUDS WITH SEVERAL
LAYERS BASED 2500-4500 FT MSL AND TOPS TO 5000-6000 FT ARE PRESENT
THROUGHOUT THE COASTAL BASIN. SATELLITE IMAGERY SHOWS CLOUDS
BEGINNING TO ERODE IN AREAS, WHICH THEY WILL CONTINUE TO DO THROUGH
THE AFTERNOON WHILE BASES GENERALLY RISE ABOVE 3000 FT MSL REGION-
WIDE. LINGERING BKN CLOUDS IN SAN DIEGO COUNTY ARE EXPECTED TO
REMAIN ALL DAY, MOSTLY FOR THE INLAND VALLEYS. LOW CLOUDS REDEVELOP
AGAIN TONIGHT BASED 1200-2000 FT MSL, THEN CLEARING AGAIN 15-17Z
MONDAY.
MOUNTAINS/DESERTS...WEST WINDS WILL GRADUALLY WEAKEN THROUGH THE
MORNING, BUT WIDESPREAD GUSTS 25-35KTS AGAIN AFTER 23Z, WEAKENING BY
06Z MONDAY.
MARINE
WEST-NORTHWEST WINDS GUSTING TO 20KT NEAR SAN CLEMENTE ISLAND
THROUGH THIS MORNING WILL CREATE LOCALLY ROUGH SEAS IN THE FAR OUTER
COASTAL WATERS. OTHERWISE, NO HAZARDOUS MARINE CONDITIONS EXPECTED
THROUGH FRIDAY.
BEACHES
ELEVATED SURF WILL IMPACT BEACHES THROUGH TONIGHT, PEAKING THIS
AFTERNOON/EARLY EVENING. EXPECTED SURF OF 3-5 FEET WITH SETS TO 6
FEET PRODUCING A HIGH RIP CURRENT RISK.
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/BEACHES...CSP
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