078
FXUS66 KSGX 181713
AFDSGX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
1013 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...
..UPDATED AVIATION DISCUSSION
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
181730Z......VFR CONDITIONS EXPECTED WITH MOSTLY SKC.
COAST...THERE IS A 20 PERCENT CHANCE OF LOW CLOUDS AND PATCHY FOG
DEVELOPING ALONG SAN DIEGO CO COASTLINE, INCL VICINITY OF KSAN AND
KCRQ, 09-16Z. IF CLOUDS DO MANAGE TO FORM ON LAND, CIGS AND VIS WILL
BE VERY LOW, 200-500 FT MSL AND 0-3 SM RESPECTIVELY. ANY CLOUD
COVERAGE CLEARS 16-18Z MON.
MARINE
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH TUESDAY. A STORM
SYSTEM MOVES INTO THE REGION WEDNESDAY THROUGH THURSDAY, BRINGING
POSSIBLE LOCAL GUSTS AROUND 20 KNOTS AND A CHANCE (10-15%) FOR
THUNDERSTORMS THURSDAY.
BEACHES
ELEVATED SURF WILL CONTINUE THROUGH MID-NEXT WEEK WITH MULTIPLE
SOUTH SWELLS MOVING IN THROUGH THIS PERIOD. SURF INCREASES SLIGHTLY
TODAY, WITH SURF 3 TO 6 FEET AND LOCAL SETS TO 7 FEET ALONG SOUTH
AND SOUTHWEST-FACING BEACHES THROUGH AT LEAST TUESDAY.
WHILE SURF AND RIP CURRENTS WILL BE ELEVATED, DAILY HIGH TIDES WILL
NOT BE PARTICULARLY HIGH, AND THE THREAT OF COASTAL FLOODING IS
MINIMAL. FURTHER DETAILS CAN BE FOUND IN THE BEACH HAZARD STATEMENT.
SKYWARN
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.
SGX WATCHES/WARNINGS/ADVISORIES
CA...BEACH HAZARDS STATEMENT THROUGH TUESDAY MORNING FOR ORANGE
COUNTY COASTAL AREAS-SAN DIEGO COUNTY COASTAL AREAS.
PZ...NONE.
PUBLIC...STEWEY
AVIATION/MARINE/BEACHES...CSP
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