978
FXUS66 KSGX 181715
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
915 AM PST WED DEC 18 2024
SYNOPSIS
SANTA ANA WINDS WILL LARGELY DIMINISH THROUGH THIS EVENING. LOCALLY
BREEZY EAST TO NORTHEASTERLY WINDS AND LOW RELATIVE HUMIDITY WILL
LINGER INTO THURSDAY. TODAY IS EXPECTED TO BE THE WARMEST DAY, WITH
A GRADUAL COOLING THURSDAY THROUGH THE WEEKEND. MARINE LAYER LOW
CLOUDS AND FOG MAY RETURN ALONG THE COAST TONIGHT, POTENTIALLY
INCREASING IN COVERAGE OVER THE WEEKEND. FOR EARLY NEXT WEEK, GUSTY
WESTERLY WIND OVER THE MOUNTAINS AND LOCALLY INTO THE DESERTS AND A
CHANCE OF SHOWERS ENTER THE FORECAST.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
AT 9 AM, SKIES WERE MOSTLY CLEAR EXCEPT FOR A PATCH OF LOCALLY DENSE
FOG ALONG THE IMMEDIATE COAST IN SOUTHERN SAN DIEGO COUNTY. THAT FOG
PATCH MAY CONTINUE TO MOVE NORTH, BUT IS NOT EXPECTED TO MAKE IT
VERY FAR INLAND, ESPECIALLY WITH THE PRESSURE GRADIENT REMAINING
OFFSHORE THROUGH THE AFTERNOON. THE LOCAL NAM-BOUNDED WRF SHOWS A
WEAK COASTAL EDDY FOR THE NEXT FEW NIGHTS WITH PATCHY LOW CLOUDS AND
FOG RETURNING FOR THE COASTAL WATERS AND ADJACENT AREAS NEAR THE
COAST FOR TONIGHT INTO THURSDAY MORNING AND AGAIN FOR THURSDAY NIGHT
INTO FRIDAY MORNING. ONCE THE EDDY GETS GOING, DENSE FOG IS LESS
LIKELY, BUT THE HREF IS SHOWING 30 TO 50 PERCENT CHANCE OF DENSE
FOG ALONG THE IMMEDIATE COAST TONIGHT INTO EARLY THURSDAY MORNING.
HIGHEST CHANCES ARE NEAR THE ORANGE/LA COUNTY LINE AND SOUTHERN
SAN DIEGO COUNTY. FOR FRIDAY THROUGH THE WEEKEND, THE MARINE LAYER
IS EXPECTED TO SLOWLY REBUILD AND SPREAD LOW CLOUDS AND FOG INTO
THE WESTERN VALLEYS.
WINDS HAVE ALREADY PEAKED THIS MORNING. THE TOP THREE WIND GUSTS
WERE 76 MPH AT ARROWHEAD SPRINGS (SAN BERNARDINO MOUNTAINS), 74 MPH
AT SILL HILL (SAN DIEGO MOUNTAINS), AND 66 MPH AT CSU SAN
BERNARDINO. A PEAK WIND GUST SUMMARY IS HEADLINED ON OUR
WEATHER.GOV/SANDIEGO WEBSITE. WINDS AT 9 AM WERE GUSTING 35 TO 50
MPH MAINLY BELOW PASSES AND ON MOUNTAIN FOOTHILLS. WINDS WILL
CONTINUE TO WEAKEN INTO THIS EVENING. LOCALLY BREEZY EAST TO
NORTHEAST WINDS ARE EXPECTED ON THE MOUNTAIN FOOTHILLS AND BELOW
PASSES TONIGHT INTO THURSDAY. HIGHS TODAY ARE EXPECTED TO WARM A
FEW TO AROUND 5 DEGREES FOR THE INLAND AREAS WITH THE COAST AND
WESTERN VALLEYS ANOTHER 5 TO 10 DEGREES WARMER THAN TUESDAY,
REACHING THE LOWER TO MID 80S FOR PORTIONS OF THE VALLEYS AND
INLAND COASTAL AREAS, AS MUCH AS 12 TO 18 DEGREES ABOVE AVERAGE.
FOR THE WEEKEND, RIDGING ALOFT IS EXPECTED OVER THE DESERT SOUTHWEST
WITH AN UPPER LEVEL TROUGH OFF THE COAST OF THE PACIFIC NORTHWEST.
THE MAIN IMPACTS FOR SOUTHERN CALIFORNIA WILL BE AN INCREASE IN HIGH
CLOUD COVERAGE AND A FEW DEGREES OF COOLING (MOST NOTICEABLE FOR
PLACES WEST OF THE MOUNTAINS). WEAK RIDGING ALOFT WILL MOVE OVER
SOUTHERN CALIFORNIA FOR MONDAY, BRINGING A FEW DEGREES OF WARMING.
FOR TUESDAY A QUICK MOVING TROUGH OF LOW PRESSURE WILL MOVE ACROSS
THE WEST COAST. THERE IS SOME UNCERTAINTY IN HOW FAR SOUTH THE LOW
WILL DIG, WHICH INTRODUCES UNCERTAINTY SURROUNDING OUR CHANCES OF
PRECIPITATION BUT AN UPTICK IN WINDS IS LOOKING LIKELY. OVERALL,
THERE IS FAIRLY HIGH CONFIDENCE IN TIMING OF WIND AND ANY POTENTIAL
PRECIPITATION OCCURRING TUESDAY AND TUESDAY NIGHT, WITH LOW
CONFIDENCE IN WIND SPEEDS AND PRECIPITATION AMOUNTS.
AVIATION
181700Z....MOSTLY CLEAR SKIES THROUGH THE AFTERNOON. AREAS OF STRONG
NORTHEAST WINDS WILL CONTINUE, BUT GRADUALLY DECREASE DURING THE
DAY. GUSTS 20-35 KNOTS ARE EXPECTED IN FOOTHILLS AND PARTS OF INLAND
VALLEYS THROUGH 19Z, WITH A GRADUAL DECREASE THEREAFTER. AREAS OF
LLWS WILL OCCUR FOR SBD, ONT, AND SNA, AS WELL AS MODERATE
UP/DOWNDRAFTS IN THE LEE (SOUTH AND WEST) OF MOUNTAINS THIS MORNING.
LOW CLOUDS DEVELOP TONIGHT, PRIMARILY REMAINING OFFSHORE. KSAN HAS
THE HIGHEST CHANCE OF A CIG TONIGHT (~20% CHANCE), PRIMARILY AFTER
02Z, WITH VIS POTENTIALLY DOWN TO 3-4SM AT TIMES THROUGH 15Z.
MARINE
NO HAZARDOUS MARINE WEATHER EXPECTED THROUGH SATURDAY. SEAS INCREASE
ON SUNDAY TO 8-10 FEET, PRIMARILY FOR THE OUTER COASTAL WATERS AND
NEAR SAN CLEMENTE ISLAND. SEAS BEGIN TO LESSEN MONDAY AND TUESDAY.
BEACHES
16-17 SECOND PERIOD WEST SWELL (270-280 DEGREES) VERY EARLY SUNDAY
WILL BRING HIGH SURF OF 8 TO 10 FEET WITH LOCALLY HIGHER SETS TO
BOTH SAN DIEGO COUNTY AND ORANGE COUNTY BEACHES FOR SEVERAL DAYS.
SURF WILL SUBSIDE A BIT BY WEDNESDAY, BUT REINFORCING LONG PERIOD
SWELLS MAY MAINTAIN ELEVATED/HIGH SURF FOR MUCH OF NEXT WEEK. HIGH
RISK OF STRONG RIP CURRENTS AND DANGEROUS SWIMMING CONDITIONS, WITH
ADDITIONAL COASTAL IMPACTS POSSIBLE.
FIRE WEATHER
SANTA ANA WINDS WILL CONTINUE INTO THIS MORNING WITH GUSTS 35 TO 45
MPH ALONG AND BELOW THE COASTAL SLOPES OF THE MOUNAINS WITH ISOLATED
GUSTS TO 50 MPH. THE WINDS WILL DIMINISH DURING THE AFTERNOON AND
EVENING. LOWEST HUMIDITY FOR INLAND AREAS WILL FALL TO 10 TO 15
PERCENT TODAY. ELEVATED FIRE WEATHER CONDITIONS WILL CONTINUE INTO
THURSDAY WITH LOCAL WIND GUSTS UP TO 35 MPH BELOW PASSES AND ON
MOUNTAIN FOOTHILLS COMBINED WITH MINIMUM DAYTIME RELATIVE HUMIDITY
10 TO 15 PERCENT FOR THE INLAND VALLEYS AND PENINSULAR MOUNTAIN
RANGES. FOR FRIDAY THROUGH SUNDAY, WEAK ONSHORE FLOW WILL RETURN
SPREADING GRADUAL COOLING AND HIGHER COASTAL HUMIDITY INLAND.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...WIND ADVISORY UNTIL NOON PST TODAY FOR ORANGE COUNTY INLAND
AREAS-RIVERSIDE COUNTY MOUNTAINS-SAN BERNARDINO COUNTY
MOUNTAINS-SAN BERNARDINO AND RIVERSIDE COUNTY VALLEYS-THE
INLAND EMPIRE-SAN DIEGO COUNTY MOUNTAINS-SAN DIEGO COUNTY
VALLEYS-SAN GORGONIO PASS NEAR BANNING-SANTA ANA MOUNTAINS
AND FOOTHILLS.
PZ...NONE.
PUBLIC/FIRE WEATHER...CO
AVIATION/MARINE...ZUBER
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