390  
FXUS66 KSGX 051010  
AFDSGX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN DIEGO CA  
310 AM PDT SUN OCT 5 2025  
   
SYNOPSIS
 
 
BELOW NORMAL TEMPERATURES THROUGH MONDAY, FOLLOWED BY A GRADUAL  
WARMING TREND INTO THE LATTER PART OF THE WEEK. AREAS OF NIGHT AND  
MORNING LOW CLOUDS AND FOG WILL CONTINUE ALONG THE COASTS AND  
PARTS OF THE VALLEYS THROUGH MIDWEEK. MID AND HIGH LEVEL TROPICAL  
MOISTURE MOVING INTO THE REGION WILL BRING A SLIGHT CHANCE OF  
SHOWERS LATE THURSDAY THROUGH SATURDAY.  
 

 
   
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
 
 
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO  
COUNTIES...  
 
LOW CLOUDS ARE PATCHY AND SLOW TO DEVELOP AGAIN THIS MORNING AS  
ONLY A WEAK MARINE INVERSION IS IN PLACE. HI-RES GUIDANCE STILL  
SUGGESTS A COASTAL EDDY SPINNING UP LATER THIS MORNING, WHICH  
WOULD HELP WITH THE DEVELOPMENT OF LOW CLOUDS ACROSS THE COASTAL  
AREAS AND FAR WESTERN VALLEYS. ELSEWHERE SKIES WILL REMAIN CLEAR.  
 
WEAK TROUGHING REMAINS ACROSS THE WESTERN US TODAY WITH A WEAK  
SHORT WAVE DROPPING SOUTH THROUGH THE PAC NW. HIGHS WILL BE A  
COUPLE DEGREES HIGHER TODAY BUT OVERALL A FEW DEGREES BELOW  
NORMAL. A CLOSED LOW DEVELOPS FROM THIS WAVE OFF THE CENTRAL CA  
COAST MONDAY AND REMAINS IN PLACE THROUGH ABOUT TUESDAY, MEANWHILE  
HIGH PRESSURE BUILDS ACROSS THE SOUTHERN US. GRADUAL HEIGHT RISES  
ACROSS SO CAL FROM THIS BUILDING HIGH PRESSURE WILL BRING MINOR  
WARMING THROUGH TUESDAY WITH HIGHS RETURNING TO AROUND NORMAL.  
THIS HIGH WILL ALSO HELP STRENGTHEN THE MARINE INVERSION, ALLOWING  
FOR MORE WIDESPREAD LOW CLOUD COVERAGE ACROSS THE COASTAL AREAS  
AND WESTERN VALLEYS EACH NIGHT AND MORNING. LITTLE CHANGE FOR  
WEDNESDAY AS THE LOW OPENS UP AND THEN PROGRESSES EASTWARD TO OUR  
NORTH.  
 
MAIN STORY THIS WEEK REMAINS THE POTENTIAL FOR TROPICAL MOISTURE  
FROM WHAT IS NOW TROPICAL STORM PRISCILLA BEING DRAWN INTO THE  
REGION LATE THURSDAY THROUGH SATURDAY. ENSEMBLE MEAN PRECIPITABLE  
WATER FROM BOTH THE EC AND GEFS ARE AROUND 1.5", WHICH ISN'T BAD  
FOR EARLY OCTOBER. HOWEVER, IT LOOKS LIKE MOST OF THIS MOISTURE  
WILL BE ABOVE THE 700 MB LEVEL. THE REAL QUESTION IS HOW MUCH  
FORCING WE'LL HAVE TO WORK WITH. INSTABILITY REMAINS WEAK WITH  
MUCAPE LESS THAN 100 J/KG, SO THUNDERSTORM PROBABILITIES ARE LESS  
THAN 10%. WHILE THERE IS LESS SPREAD AMONGST THE ENSEMBLES WITH  
RESPECT TO THE POSITION OF THE LARGE UPPER LOW OFF THE COAST  
DURING THIS PERIOD, ENOUGH SPREAD REMAINS THAT UNCERTAINTY IN  
FORCING AND THEREFORE RAINFALL AMOUNTS REMAIN. WITH THE LOW  
FURTHER WEST, PLACING US MORE UNDER THE INFLUENCE OF THE RIDGE TO  
THE EAST, ACCUMULATING PRECIPITATION WILL BE HARDER TO COME BY. A  
FURTHER WEST TRACK OF THE LOW WOULD PROVIDE A LITTLE MORE LIFT AND  
PRECIPITATION. GIVEN THE LACK OF STRONG DYNAMICS EITHER WAY, THIS  
GENERALLY LOOKS LIKE A CASE WHERE RAINFALL RATES WILL REMAIN ON  
THE LOW END ABSENT ANY THUNDERSTORMS DEVELOPING, REALLY LIMITING  
THE FLOODING THREAT. NBM 10TH/90TH PERCENTILE 48 HR RAINFALL  
ACCUMULATIONS RANGE FROM ZERO TO AROUND AN INCH FOR LATE THU-LATE  
SAT, THOUGH THE 90TH PERCENTILE IS DEFINITELY SKEWED BY A COUPLE  
OF VERY WET ENSEMBLE MEMBERS. NBM MEAN IS CLOSER TO 0.2-0.3".  
ENSEMBLE PW FALLS OFF A CLIFF ON SUNDAY AS THE UPPER TROUGH  
PASSES, PUSHING TROPICAL MOISTURE OUT OF THE AREA. HIGHS WILL  
REMAIN NEAR NORMAL THROUGH FRIDAY, THEN A COOLING TREND FOLLOWS  
FOR SATURDAY AND SUNDAY AS THE TROUGH MOVES THROUGH.  
 

 
   
AVIATION
 
 
050930Z....COASTS/VALLEYS...CURRENTLY SKC EXCEPT A FEW PATCHES OF  
LOW CLOUDS OVER NEARSHORE WATERS. CLOUDS BASED 1800-2400 FT MSL  
SHOULD DEVELOP AND FILL INTO MOST OF COASTAL SAN DIEGO COUNTY/ORANGE  
COUNTIES AFTER 12Z. 10 TO 15 MILES INLAND EXTENT AT MOST. CLOUDS  
MOSTLY SCATTER OUT 17-19Z, BUT MAY LINGER TO 21Z AT THE IMMEDIATE  
COASTLINE. CLOUDS WITH SIMILAR BASES WILL START TO DEVELOP AFTER 00Z  
MON AT THE COAST, BROADENING IN COVERAGE, AND EVENTUALLY FILLING  
INTO SD/ORANGE COUNTY VALLEYS OVERNIGHT.  
 
MOUNTAINS/DESERTS...VFR CONDITIONS WILL PREVAIL INTO MONDAY MORNING.  
 

 
   
MARINE
 
 
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH THURSDAY  
MORNING.  
 

 
   
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...SS  
AVIATION/MARINE...KW  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab CA Page Main Text Page