743
FXUS66 KSGX 180829
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
129 AM PDT SUN OCT 18 2026
SYNOPSIS
SOME COOLING EXPECTED FOR THE COASTAL BASIN TODAY AS ONSHORE FLOW
RETURNS. FURTHER COOLING EXPECTED ACROSS THE REGION STARTING TUESDAY
AS A LOW-PRESSURE SYSTEM BEGINS TO MOVE IN FROM THE NORTHWEST. THIS
WILL BRING WIDESPREAD LIGHT TO MODERATE RAIN TO THE REGION LATE
WEDNESDAY INTO THURSDAY ALONG WITH ELEVATED SOUTHWEST WINDS FOR THE
MOUNTAINS AND DESERTS.
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
SANTA ANA WINDS ARE FINALLY DIMINISHING THIS EVENING AS EASTERLY
FLOW ALOFT AND THE OFFSHORE SURFACE PRESSURE GRADIENT BOTH CONTINUE
TO WEAKEN. EASTERLY GUSTS 20-35 MPH WILL CONTINUE ALONG COASTAL
SLOPES AND THROUGH EAST-TO-WEST PASSES THROUGH THIS MORNING. RETURN
OF WEAK ONSHORE FLOW WILL ALLOW FOR SOME COOLING TODAY, ESPECIALLY
FOR COASTAL AREAS, THOUGH HIGHS WILL REMAIN 4 TO 10 DEGREES ABOVE
NORMAL THROUGH THE COASTAL BASIN.
THE RETURN OF ONSHORE FLOW WILL ALSO HERALD THE RETURN OF THE MARINE
LAYER. HREF GUIDANCE INTRODUCES PATCHY LOW CLOUDS AND FG OVER
COASTAL WATERS STARTING EARLY MONDAY MORNING. ONSHORE FLOW INCREASES
BY MONDAY NIGHT AS A CLOSED UPPER LOW FROM THE NORTHWEST BEGINS TO
INFLUENCE THE REGION. THIS WILL ALLOW MARINE LAYER CLOUDS AND FG TO
PUSH INTO COASTAL AREAS AND PORTIONS OF THE VALLEYS.
AS THE UPPER LOW CONTINUES TO SLIDE SOUTHWARD, COOLING WILL SPREAD
ACROSS THE REGION WITH BELOW NORMAL HIGHS EXPECTED FROM TUESDAY
ONWARD. RAIN CHANCES INCREASE FROM WEST TO EAST ON WEDNESDAY, THOUGH
THE MAJORITY OF GUIDANCE HAS TRENDED A LITTLE SLOWER WITH THE ONSET
OF PRECIPITATION. REGARDLESS, WIDESPREAD LIGHT TO MODERATE RAIN IS
EXPECTED WITH THE MOST LIKELY TIMEFRAME FOR PRECIP BEING WEDNESDAY
NIGHT INTO THURSDAY. AS THE EVENT DRAWS CLOSER, SOME DETAILS ARE
BEGINNING TO EMERGE. NBM PROBABILITIES OF STORM TOTAL RAINFALL
EXCEEDING 0.5" AND 1" FROM THE COAST TO THE MOUNTAINS ARE ABOUT 60-
90% AND 25-55% RESPECTIVELY. THE HIGHER PROBABILITIES ARE MAINLY
FOCUSED IN THE MOUNTAINS AND PORTIONS OF THE COASTAL BASIN NORTH OF
SAN DIEGO COUNTY. LOWER RAINFALL TOTALS ARE EXPECTED IN THE DESERTS
WITH ONLY 30-50% AND 5-25% CHANCES OF 0.5" OF RAINFALL IN THE HIGH
DESERT AND LOW DESERTS, RESPECTIVELY.
AS THE CORE OF THE LOW MOVES OVERHEAD ON THURSDAY, TEMPERATURES WILL
FALL WELL BELOW NORMAL ACROSS THE REGION. ADDITIONALLY, INCREASED
MID-LEVEL LAPSE RATES AND VORTICITY WILL PROMOTE DEVELOPMENT OF
CONVECTIVE SHOWERS. THERE IS ABOUT A 10-15% CHANCE FOR THUNDERSTORMS
FROM THE COAST TO THE MOUNTAINS AT THIS TIME. IF THUNDERSTORMS
DEVELOP, LOCALLY HEAVY RAINFALL RATES WILL BE POSSIBLE.
MODEL SOLUTIONS DIVERGE BY NEXT WEEKEND, BUT THERE IS NOT MUCH
INDICATION OF ANY SIGNIFICANT WEATHER. THE MEAN OF THE GUIDANCE
INDICATES MAINLY ZONAL FLOW WITH TEMPERATURES WARMING BACK TO
SLIGHTLY BELOW NORMAL THROUGH THE WEEKEND. IN THE LONG TERM, THERE
IS SOME INDICATION THAT THE TROUGHING PATTERN WILL CONTINUE.
AVIATION
180600Z...EASTERLY OFFSHORE WINDS HAVE LARGELY SUBSIDED AT THE
SURFACE, THOUGH ELEVATED EASTERLY WINDS REMAIN POSSIBLE NEAR THE IN
THE MOUNTAINS AND AT 4000-8000FT INTO THE EARLY OVERNIGHT HOURS.
OTHERWISE...VFR CONDITIONS EXPECTED WITH SCT-BKN HIGH CLOUDS AOA
10,000FT MSL THROUGH THIS EVENING. HIGH CLOUDS SCATTER OUT ACROSS
THE AREA TONIGHT, WITH SKC THEREAFTER.
MARINE
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH WEDNESDAY.
BEACHES
ELEVATED SURF WILL CONTINUE THIS WEEKEND INTO MID-NEXT WEEK WITH
MULTIPLE SOUTH SWELLS MOVING IN THROUGH THIS PERIOD. SURF INCREASES
SLIGHTLY SUNDAY, WITH SURF 3 TO 6 FEET AND LOCAL SETS TO 7 FEET
ALONG SOUTH AND SOUTHWEST-FACING BEACHES THROUGH AT LEAST WEDNESDAY.
WHILE SURF AND RIP CURRENTS WILL BE ELEVATED, DAILY HIGH TIDES WILL
NOT BE PARTICULARLY HIGH, AND THE THREAT OF COASTAL FLOODING IS
MINIMAL.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...BEACH HAZARDS STATEMENT FROM 9 AM PDT THIS MORNING THROUGH
TUESDAY MORNING FOR ORANGE COUNTY COASTAL AREAS-SAN DIEGO
COUNTY COASTAL AREAS.
PZ...NONE.
PUBLIC...KW
AVIATION/MARINE/BEACHES...MUNYAN
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