319
FXUS66 KSGX 191103
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
303 AM PST THU DEC 19 2024
SYNOPSIS
AS OFFSHORE BREEZES DECREASE, TEMPERATURES WILL BEGIN TO DECREASE
WHILE THE HUMIDITY INCREASES FOR THE NEXT FEW DAYS. AREAS OF COASTAL
FOG WILL CONTINUE THIS MORNING AND AGAIN TONIGHT INTO FRIDAY.
THE MARINE LAYER WILL DEEPEN THROUGH THE WEEKEND, EXTENDING THE
LOW CLOUDS AND FOG FARTHER INLAND IN THE NIGHTS AND MORNINGS. A
LOW PRESSURE SYSTEM IS EXPECTED TO BRING WESTERLY WINDS AND A
CHANCE OF SHOWERS LATE ON CHRISTMAS EVE.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
COASTAL FOG THAT HAD SOCKED IN THE COAST LAST EVENING HAS BACKED
OFF IN SAN DIEGO COUNTY, PROBABLY IN RESPONSE TO THE WEAK
OFFSHORE FLOW IN PLACE. THE COASTAL EDDY THAT HELPED THAT FOG DECK
DEVELOP AND MIGRATE NORTH ALONG THE COAST HAS DISSOLVED AS THE
OFFSHORE FLOW REASSERTS ITSELF. STILL, WATCH FOR SOME DENSE FOG
NEAR THE COAST THIS MORNING. NOT FAR INLAND IT WILL CONTINUE VERY
DRY AND WARM TODAY, BUT THE COAST WILL REMAIN CLAMMY UNDER A VERY
SHALLOW MARINE LAYER. COASTAL DENSE FOG COULD BECOME AN ISSUE
AGAIN TONIGHT INTO FRIDAY. OVER THE NEXT FEW DAYS, HIGH PRESSURE
ALOFT WEAKENS AND WEAK ONSHORE FLOW GAINS THE UPPER HAND. THAT
WILL HELP THE MARINE LAYER DEEPEN SO THAT COASTAL LOW CLOUDS AND
FOG WILL EXTEND A LITTLE FARTHER INLAND EACH NIGHT AND MORNING
THROUGH SUNDAY. AND THAT SHOULD HELP IMPROVE VISIBILITY AT THE
COAST AFTER FRIDAY MORNING. ALSO, THERE WILL BE WAVES OF HIGH
CLOUDS FILTERING OUR SUNSHINE FROM TIME TO TIME. A COOLING TREND
WILL BEGIN AT THE COAST AND WESTERN VALLEYS TODAY, BUT NOT YET
INLAND. IT WILL BE COOLER REGIONWIDE EACH DAY FRIDAY THROUGH
SUNDAY. A BRIEF HIGH PRESSURE RIDGE WILL BRING A SLIGHTLY WARMER
DAY MONDAY. THE JET STREAM IS IN A GOOD POSITION TO SEND TROUGHS
OF LOW PRESSURE REGULARLY INTO THE WEST COAST, AND IT LOOKS LIKE
IN SOCAL A WAVE OF LOW PRESSURE AMPLIFIES ENOUGH SO WE WILL FINALLY
GET OUR TURN TO GET SOME RAIN. ONSHORE WESTERLY WINDS WILL
INCREASE TUESDAY AND PEAK TUESDAY NIGHT, STRONGEST IN THE
MOUNTAINS AND DESERTS. IT LOOKS LIKE THE RAIN WILL ARRIVE RIGHT
ABOUT THE TIME WE GET A VISIT FROM SANTA CLAUS ON CHRISTMAS EVE. A
VERY PRELIMINARY GUESS ON RAINFALL WOULD BE LESS THAN 0.10 INCH
AND MAYBE UP TO 0.25 INCH IN MOUNTAINS. IT'S NOT A COLD SYSTEM, SO
SNOW LEVELS APPEAR TO STAY MOSTLY ABOVE 8,000 FEET. THIS FAST-
MOVING SYSTEM WILL DEPART AS FAST AS SANTA DOES ON CHRISTMAS
MORNING, LEAVING GIFTS OF FAIR AND SEASONAL WEATHER IN ITS WAKE.
AVIATION
191100Z....COASTS/VALLEYS...FOG AND LOW CLOUDS (BASED AROUND 100-
200FT MSL WITH TOPS TO 400FT MSL) SURGED INLAND AND NORTHWARD
THROUGH COASTAL ORANGE COUNTY OVERNIGHT BUT WEAK OFFSHORE FLOW HAS
HELPED TO CLEAR THE FOG BACK TO THE COAST IN MANY SPOTS. NORTHERN
ORANGE COUNTY (INCLUDING KSNA) AND SOUTHERN SAN DIEGO COUNTY
(INCLUDING KSAN) ARE STILL SEEING STUBBORN PATCHES HANG ON AT THIS
HOUR, BUT SHOULD ALSO END UP CLEARING BY 12-14Z. LOW CLOUDS LOOK TO
FILL BACK IN AND PUSH ASHORE AROUND 23-01Z THURSDAY EVENING,
REACHING 5-10 MILES INLAND BY 06Z. BASES LOOK TO BE A TOUCH HIGHER
THAN THIS MORNING, LIKELY AROUND 300-600FT MSL. VIS RESTRICTIONS 0-
3SM POSSIBLE IN INLAND VALLEYS, COASTAL MESAS, AND WHERE CLOUDS
INTERSECT HIGHER TERRAIN, WITH 2-5SM FOR THE IMMEDIATE COASTS.
MOUNTAINS/DESERTS
ASIDE FROM HIGH CLOUDS AT OR ABOVE 20,000FT MSL
FILLING IN TODAY, MOSTLY CLEAR CONDITIONS AND UNRESTRICTED VIS
CONTINUES THROUGH EARLY FRIDAY MORNING.
MARINE
AREAS OF DENSE FOG WITH VISIBILITY 1 NM OR LESS WILL PERSIST THIS
MORNING BEFORE LIFTING/CLEARING A FEW HOURS AFTER SUNRISE. FOG IS
POSSIBLE AGAIN THURSDAY EVENING INTO FRIDAY MORNING, BUT SHOULD BE
PATCHIER THAN THIS MORNING. LONG PERIOD WEST SWELL LATE SATURDAY
WILL GENERATE SEAS OF 8-11 FEET SUNDAY THROUGH WEDNESDAY, PRIMARILY
FOR THE OUTER COASTAL WATERS AND NEAR SAN CLEMENTE ISLAND.
BEACHES
A SERIES OF 16-17 SECOND PERIOD WEST SWELLS (280-290 DEGREES)
BEGINNING SUNDAY WILL BRING HIGH SURF OF 7 TO 9 FEET WITH LOCALLY
HIGHER SETS PRIMARILY TO SAN DIEGO COUNTY BEACHES WHILE ORANGE
COUNTY BEACHES WILL SEE SURF CLOSER TO 3 TO 6 FEET. 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
ELEVATED FIRE WEATHER CONDITIONS WILL CONTINUE THIS MORNING.
LOCAL EAST WINDS WILL GUST UP TO 30 MPH BELOW PASSES AND ON
MOUNTAIN FOOTHILLS, AND COMBINE WITH MINIMUM DAYTIME RELATIVE
HUMIDITY OF 10 TO 15 PERCENT FOR THE INLAND VALLEYS AND PENINSULAR
MOUNTAIN RANGES. ONSHORE FLOW WILL RETURN FRIDAY, SPREADING
HIGHER COASTAL HUMIDITY FARTHER INLAND.
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/FIRE WEATHER...MM
AVIATION/MARINE/BEACHES...MUNYAN
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