554
FXUS66 KSGX 220511
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
911 PM PST SAT DEC 21 2024
SYNOPSIS
PATCHY DENSE FOG IS POSSIBLE OVER HIGHER COASTAL TERRAIN TONIGHT,
WITH HIGH CLOUDS ELSEWHERE. NEAR AVERAGE TEMPERATURES EXPECTED
NEAR THE COAST WITH ABOVE NORMAL TEMPERATURES INLAND THROUGH
MONDAY. BREEZIER, COOLER, AND WETTER WEATHER IS EXPECTED FOR
TUESDAY. DRY WEATHER IS EXPECTED FOR THE MIDDLE TO END OF NEXT
WEEK, WITH A WARMING TREND INTO NEXT WEEKEND.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
EVENING UPDATE...
VERY PATCHY LOW CLOUDS ARE DEVELOPING AND SUBSEQUENTLY DISSIPATING
OVER THE SAN DIEGO COUNTY COASTAL AREAS THIS EVENING ALONG WITH
BANDS OF HIGH CLOUDS MOVING IN FROM THE NORTH-NORTHWEST. THE 00Z
KNKX SOUNDING SHOWS THE MARINE INVERSION BASED NEAR 1100 FT MSL.
GIVEN THIS, EXPECT THE FOCUS OF DENSE FOG TO BE OVER THE HIGHER
COASTAL TERRAIN AND COASTAL MESAS AS OPPOSED TO ALONG THE
IMMEDIATE COAST. THIS COULD IMPACT TRAVEL ON I-15 AND HIGHWAY 163
IN SAN DIEGO COUNTY AND I-5 IN ORANGE COUNTY AT TIMES TONIGHT INTO
SUNDAY MORNING. OTHERWISE MINOR COOLING SUNDAY AS A WEAK TROUGH
MOVES ACROSS SO CAL, THOUGH HIGHS REMAIN AROUND 5-10 DEGREES ABOVE
NORMAL INLAND. TEMPERATURES REBOUND SLIGHTLY ON MONDAY WITH
TRANSITORY UPPER LEVEL RIDGING FOLLOWS BEHIND THE UPPER TROUGH.
PREVIOUS DISCUSSION...
ON TUESDAY A QUICK MOVING TROUGH OF LOW PRESSURE WILL MOVE ACROSS
THE WEST COAST BRINGING BREEZY, WET, AND COOL CONDITIONS TO THE
AREA. ONSHORE WESTERLY WINDS WILL INCREASE TUESDAY AND PEAK TUESDAY
NIGHT, STRONGEST IN THE MOUNTAINS, THROUGH PASSES, AND LOCALLY INTO
THE DESERTS. PRELIMINARY GUIDANCE SHOWS PEAK WIND GUSTS OF 35-45
MPH, LOCALLY UP TO 55 MPH IN WIND PRONE LOCATIONS. GUIDANCE IS
FAIRLY CONSISTENT ON THE TIMING BEING TUESDAY AFTERNOON AND EVENING
FOR BOTH THE UPTICK IN WIND AND PRECIPITATION. DETERMINISTIC
INTEGRATED WATER VAPOR TRANSPORT GUIDANCE FOR BOTH THE GFS AND ECMWF
IS SHOWING A WEAK MOISTURE SURGE REACHING THE SOUTHERN CALIFORNIA
COAST TUESDAY EVENING. ALMOST ALL INDIVIDUAL ENSEMBLE MEMBERS FOR
THE ECMWF AND GEFS ARE SHOWING MEASURABLE PRECIPITATION FOR PLACES
WEST OF THE MOUNTAINS FOR TUESDAY AFTERNOON/NIGHT. THERE DOES STILL
REMAIN SOME UNCERTAINTY IN RAINFALL AMOUNTS, ALTHOUGH MOST GUIDANCE
IS INDICATING RAINFALL WILL BE LIGHT. FORECAST RAINFALL TOTALS HAVE
INCREASED SLIGHTLY SINCE THIS MORNING. FOR THE COAST AND VALLEYS
TOTALS ARE EXPECTED TO BE 0.05-0.12", WITH TOTALS 0.20-0.30" ON THE
COASTAL SLOPES OF THE MOUNTAINS. A DUSTING OF SNOW IS EXPECTED ABOVE
7000 FT. THE TROUGH IS EXPECTED TO QUICKLY EXIT TO THE EAST, LEAVING
DRY CONDITIONS IN IT'S WAKE FOR MUCH OF WEDNESDAY.
TEMPERATURES ON WEDNESDAY ARE EXPECTED TO BE NEAR TO SLIGHTLY BELOW
NORMAL FOR THIS TIME OF YEAR WEST OF THE MOUNTAINS AND 3 TO 7 DEGREE
WARMER THAN NORMAL IN THE DESERTS. LOWER DESERT LOCATIONS WILL HAVE
HIGHS IN THE 70S WITH WIDESPREAD 60S WEST OF THE MOUNTAINS. A
GRADUAL WARMING TREND IS EXPECTED THURSDAY THROUGH SATURDAY AS
RIDGING BUILDS OVER CALIFORNIA.
AVIATION
220500Z....COASTS/VALLEYS...AREAS OF BKN-OVC LOW CLOUDS/FOG WILL
CONTINUE TO DEVELOP WITHIN 10-15 MILES OF THE COAST THROUGH 09Z SUN,
THEN CONTINUING THROUGH 16Z-19Z SUN. BASES WILL BE VARIABLE, MOSTLY
500-900 FT MSL THROUGH 08Z SUN, THEN LOWERING TO 300-600 FT MSL 08Z-
16Z SUN BEFORE LIFTING TO 500-900 FT MSL 16Z-19Z AS SKIES MOSTLY
CLEAR. TOPS WILL MOSTLY BE 700-1100 FT MSL. AREAS OF VIS 2-5 MILES
WILL OCCUR WITHIN 15 MILES OF THE COAST WITH LOCAL VIS BELOW 1 MILE
OVER MAINLY HIGHER COASTAL TERRAIN 08Z-17Z SUN. HIGHER COASTAL
TERRAIN WILL BE OBSCURED AT TIMES THROUGH 17Z SUN. LOCAL BKN CIGS
COULD CONTINUE AT THE BEACHES SUN AFTERNOON. STRATUS WILL HAVE
HIGHER BASES SUN EVENING AS IT SPREADS INLAND, MOST LIKELY 700-1200
FT MSL.
PROBABILITIES OF LOWEST CIGS THROUGH 17Z SUN AT SAN AND SNA,
RESPECTIVELY:
200 FEET OR LESS: 15 PERCENT, 25 PERCENT
500 FEET OR LESS: 60 PERCENT, 80 PERCENT
PROBABILITIES OF LOWEST VIS THROUGH 17Z SUN AT SAN AND SNA,
RESPECTIVELY:
1/2 MILE OR LESS: 15 PERCENT, 25 PERCENT
1 MILE OR LESS: 30 PERCENT, 40 PERCENT
2 MILES OR LESS: 60 PERCENT, 70 PERCENT
MOUNTAINS/DESERTS
SCT-BKN HIGH CLOUDS AT/ABOVE 20000 FT MSL WITH
UNRESTRICTED VIS WILL PREVAIL THROUGH SUN EVENING.
MARINE
LONG PERIOD WNW SWELLS (280-290 DEG) OF 8-11 FEET WILL BUILD LATE
TONIGHT, CONTINUING SUNDAY THROUGH TUESDAY NIGHT, WITH THE HIGHEST
SWELLS IN THE OUTER COASTAL WATERS WHERE A SMALL CRAFT ADVISORY IS
IN EFFECT. 8-9 FOOT WAVES COULD OCCUR WITHIN 30 NM OF THE COAST BUT
WITH RELATIVELY LONG PERIODS OF 16-20 SECONDS. WIND GUSTS OF 20-25
KT ARE EXPECTED TUESDAY NIGHT IN THE OUTER COASTAL WATERS.
BEACHES
LONG PERIOD (16-20 SECOND) WEST TO NORTHWEST SWELLS (280-290 DEG)
WILL ARRIVE EARLY SUNDAY AND RESULT IN HIGH SURF OF 6-12 FEET WITH
LOCALLY HIGHER SETS THROUGH WEDNESDAY. THIS WILL MAKE SWIMMING
HAZARDOUS AND POSE A MINOR COASTAL FLOODING THREAT. ELEVATED SURF
WILL CONTINUE LATE IN THE WEEK AS ADDITIONAL, ALBEIT SOMEWHAT
SMALLER SWELLS OCCUR. SEE THE HIGH SURF ADVISORY FOR MORE DETAILS.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...HIGH SURF ADVISORY UNTIL 4 AM PST WEDNESDAY FOR ORANGE COUNTY
COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS.
PZ...SMALL CRAFT ADVISORY UNTIL 4 AM PST WEDNESDAY FOR WATERS FROM
SAN MATEO POINT TO THE MEXICAN BORDER EXTENDING 30 TO 60 NM
OUT INCLUDING SAN CLEMENTE ISLAND.
PUBLIC...SS/CO
AVIATION/MARINE/BEACHES...MAXWELL
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