401
FXUS66 KSGX 182139
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
139 PM PST WED DEC 18 2024
SYNOPSIS
SANTA ANA WINDS WILL CONTINUE TO DECREASE INTO THURSDAY MORNING.
LOCALLY BREEZY EAST TO NORTHEASTERLY WINDS AND LOW RELATIVE
HUMIDITY WILL LINGER INTO THURSDAY, CREATING ELEVATED FIRE WEATHER
CONDITIONS. CONDITIONS WILL GRADUALLY COOL THURSDAY THROUGH THE
WEEKEND. MARINE LAYER LOW CLOUDS AND FOG MAY RETURN ALONG THE
COAST TONIGHT, INCREASING IN COVERAGE OVER THE WEEKEND. GUSTY
WESTERLY WINDS OVER THE MOUNTAINS INTO THE DESERTS AND A CHANCE
OF SHOWERS ENTERS THE FORECAST ON TUESDAY.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
AT 1 PM PATCHY FOG WAS STILL LINGERING ALONG THE SOUTHERN SAN DIEGO
COUNTY COAST. THAT FOG PATCH MAY MOVE NORTH UP THE COAST INTO
TONIGHT, BUT IS NOT EXPECTED TO MAKE IT VERY FAR INLAND ESPECIALLY
WITH THE PRESSURE GRADIENT REMAINING OFFSHORE THROUGH THE EVENING.
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.
FRIDAY THROUGH THE WEEKEND, THE MARINE LAYER IS EXPECTED TO SLOWLY
REBUILD AND SPREAD LOW CLOUDS AND FOG INTO THE WESTERN VALLEYS BY
SUNDAY MORNING.
WINDS THIS AFTERNOON HAVE WEAKENED AND BECOME MUCH MORE LOCALIZED.
LOCALLY BREEZY EAST TO NORTHEAST WINDS ON THE MOUNTAIN FOOTHILLS AND
BELOW PASSES WILL CONTINUE INTO EARLY 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 FROM THAT TROUGH 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(CURRENTLY AT 25 TO 35
PERCENT IN AND WEST OF THE MOUNTAINS) BUT AN UPTICK IN WINDS FOR THE
MOUNTAINS AND DESERTS 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
182100Z....COASTS/VALLEYS...LOW CLOUDS AND FG DEVELOP TONIGHT AND
WILL TRY TO PUSH INLAND SOUTH TO NORTH, BUT SHOULD PRIMARILY REMAIN
OFFSHORE. KSAN HAS THE HIGHEST CHANCE OF IMPACTS TONIGHT (~40%
CHANCE), PRIMARILY AFTER 02Z, WITH VIS POTENTIALLY DOWN TO 3-4SM AT
TIMES THROUGH 15Z. OTHER COASTAL LOCATIONS MAY SEE PERIODIC VIS
REDUCTIONS DOWN TO 4SM AND LOCALIZED DOWN TO 1SM OR LOWER FOR THE
COASTAL TERRAIN GENERALLY AFTER 05Z. CLEARING ALONG THE COASTS
SHOULD OCCUR BY 15-17Z, WITH VFR AND FEW250 PREVAILING BEYOND THAT.
MOUNTAINS/DESERTS
MOSTLY CLEAR SKIES THROUGH THURSDAY MORNING.
AREAS OF NORTHEAST WINDS ABOVE 25 MPH WILL CONTINUE THIS EVENING,
BUT WILL CONTINUE TO DECREASE THROUGH THE NIGHT. HIGH CLOUDS RETURN
THURSDAY AFTERNOON WITH BASES GENERALLY AT OR ABOVE 20,000FT MSL.
MARINE
PATCHY DENSE FOG POSSIBLE TONIGHT AND THURSDAY NIGHT WITH VISIBILITY
DOWN TO 1 NM AT TIMES. OTHERWISE, NO HAZARDOUS MARINE WEATHER
EXPECTED THROUGH SATURDAY. LONG PERIOD WEST SWELL LATE SATURDAY WILL
GENERATE SEAS OF 8-11 FEET ON SUNDAY AND MONDAY, PRIMARILY FOR THE
OUTER COASTAL WATERS AND NEAR SAN CLEMENTE ISLAND. SEAS BEGIN TO
LESSEN MONDAY NIGHT INTO TUESDAY.
FIRE WEATHER
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 EARLY NEXT WEEK, ONSHORE FLOW WILL RETURN SPREADING GRADUAL
COOLING AND HIGHER COASTAL HUMIDITY INLAND. WESTERLY WINDS ARE
EXPECTED TO INCREASE OVER THE MOUNTAINS AND LOCALLY INTO THE DESERTS
TUESDAY, ALONG WITH A 20 TO 35 PERCENT CHANCE OF RAIN SHOWERS
(HIGHEST CHANCES IN THE MOUNTAINS).
SGX WATCHES/WARNINGS/ADVISORIES
CA...NONE.
PZ...NONE.
PUBLIC/FIRE WEATHER...CO
AVIATION/MARINE...ZUBER
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