409  
FXUS66 KSGX 242051  
AFDSGX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN DIEGO CA  
151 PM PDT MON SEP 24 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE ALOFT WILL BUILD IN FROM THE WEST AND EVENTUALLY  
OVERHEAD SOUTHERN CALIFORNIA BY THURSDAY. THIS WILL LEAD TO  
BUILDING HEAT INLAND WEDNESDAY THROUGH THURSDAY. FOR FRIDAY INTO  
THE UPCOMING WEEKEND, AN UPPER LEVEL LOW OFF THE WEST COAST WILL  
MOVE INLAND INTO NORTHERN CALIFORNIA, BRINGING STRONGER ONSHORE  
FLOW AND A COOLING TREND FOR SOUTHERN CALIFORNIA.  
 

 
   
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
 
 
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO  
COUNTIES...  
 
THE MARINE LAYER STRATUS HAS HUNG IN TOUGH OVER SAN DIEGO COUNTY  
TODAY WITH CLOUDS SOCKED IN HERE EVEN AT THE OFFICE IN RB THIS  
AFTERNOON! EVEN SOME LIGHT MIST/DRIZZLE HAS BEEN OBSERVED HERE  
AND REPORTED ELSEWHERE. GOES SATELLITE LOOP DOES SHOW THINNING  
OF THE CLOUD DECK OCCURRING, SO SOME SUN IS POSSIBLE WHERE IT IS  
CURRENTLY CLOUDY, THOUGH LOOKING LESS LIKELY THAN EARLIER  
ANTICIPATED.  
 
THE STRATUS DECK WILL MOVE INLAND AGAIN SOME 25 MILES AND OVER  
ORANGE COUNTY INTO NORTHWESTERN PARTS OF THE INLAND EMPIRE. AGAIN,  
PATCHY DRIZZLE WILL BE POSSIBLE. WRF SHOWS CLOUDS AGAIN SLOW TO  
CLEAR ON TUESDAY AND HAVE FOLLOWED THIS TREND.  
 
HEIGHTS WILL BE RISING AS AN UPPER LEVEL RIDGE BUILDS IN FROM THE  
WEST AND EVENTUALLY BECOMES CENTERED OVER SOUTHERN CALIFORNIA BY  
THURSDAY. THIS WILL LEAD TO WARMING TEMPS WITH HOT CONDITIONS  
INLAND WEDNESDAY-THURSDAY. HEAT RISK DOESN'T SUPPORT HEAT  
HEADLINES, BUT HAVE INCREASED HIGH TEMPERATURES WEDNESDAY-THURSDAY  
WITH SOME TRIPLE DIGITS FOR PARTS OF THE INLAND EMPIRE AND TO  
AROUND 110F FOR THE COACHELLA VALLEY. THE COAST WILL PEAK AT NEAR  
80F WITH INLAND OC METRO AND THE INLAND VALLEYS OF SD INTO THE  
LOWER TO MID 90S.  
 
AN UPPER LEVEL LOW WILL CUT OFF AND APPROACH THE CALIFORNIA COAST  
BY FRIDAY AND EVENTUALLY MOVE ACROSS NORCAL THIS WEEKEND. THIS  
WILL DISPLACE THE UPPER RIDGE TO THE SOUTHEAST WITH LOWERING  
HEIGHTS ACROSS SOCAL. SO GRADUAL COOLING IS EXPECTED FRIDAY AND  
INTO THE WEEKEND, BUT STILL REMAINING SLIGHTLY ABOVE LATE  
SEPTEMBER AVERAGES. WINDS COULD BECOME GUSTY AND LOCALLY STRONG ON  
THE DESERT MOUNTAIN SLOPES AND PORTIONS OF THE DESERTS EACH  
AFTERNOON AND EVENING THIS WEEKEND.  
 
THE WEATHER FOR THE FIRST WEEK OF OCTOBER IS CERTAINLY INTERESTING  
TO LOOK AT BUT IS HIGHLY UNCERTAIN. SEVERAL RUNS OF THE GFS ARE  
PULLING A TROPICAL SYSTEM NORTH INTO NORTHERN BAJA CENTERED  
AROUND OCTOBER 2ND, WHILE THE ECMWF KEEPS THE SYSTEM SOUTH OF 20N.  
A LOOK AT THE 24.00Z GFS ENSEMBLE RUNS SHOWS THAT 4 OF 12 MEMBERS  
BRING SOME TROPICAL MOISTURE INTO SOCAL. GIVEN THAT THE ENSEMBLE  
MEAN KEEPS THE TROPICAL MOISTURE AWAY, ALONG WITH THE ECMWF, AM  
FAVORING THIS SCENARIO. HOWEVER, WE OF COURSE WILL CONTINUE TO  
MONITOR THIS IN THE DAYS AHEAD FOR BETTER MODEL CONTINUITY.  
 
INTERESTINGLY, WHILE THE 24.12Z RUN OF THE ECMWF CONTINUES TO KEEP  
THE TROPICAL SYSTEMS LOCKED WELL TO THE SOUTH, IT ACTUALLY DOES  
SHOW SOME LIGHT RAIN OVER SOCAL EARLY NEXT WEEK, BUT NOT FROM THE  
TROPICS, RATHER A DEEP PACIFIC TROUGH.  
 

 
   
FIRE WEATHER
 
 
WEAK OFFSHORE FLOW WILL BEGIN TUESDAY AND LAST THROUGH THURSDAY.  
EASTERLY WINDS WILL PREVAIL WITH GUSTS TO ABOUT 20-25 MPH OVER THE  
MOUNTAINS AND COASTAL MOUNTAIN SLOPES, AS WELL AS THROUGH THE  
PASSES, BUT WEAKER WINDS ARE FORECAST FOR LOWER ELEVATIONS. THE  
WESTERLY SEA BREEZE WILL KICK IN EACH DAY. STILL, RELATIVE  
HUMIDITY WILL LOWER WITH RHS IN THE TEENS INTO THE INLAND EMPIRE,  
THE FAR EASTERLY SAN DIEGO COUNTY VALLEYS AS WELL AS OVER THE  
MOUNTAINS AND DESERTS, RESULTING IN ELEVATED FIRE WEATHER CONCERNS  
DURING THIS PERIOD. BY FRIDAY, WINDS WILL BECOME ONSHORE WITH  
GRADUALLY MODIFYING RHS, EXCEPT ACROSS THE DESERTS.  
 

 
   
AVIATION
 
 
242000Z...COAST/VALLEYS...A SOLID OVERCAST PERSISTED OVER KSAN AND  
KCRQ THIS MORNING WITH PILOTS REPORTING BASES NEAR 1300 FEET AND  
TOPS NEAR 2800 FT. DRIZZLE WAS REPORTED IN SOME AREAS. CIGS WILL  
LIKELY CONTINUE AT KSAN AND KCRQ THROUGH TONIGHT, BUT A BRIEF PERIOD  
OF CLEARING IS POSSIBLE TODAY BETWEEN 22Z-02Z.  
 
SKIES CLEARED AT KSNA AT 19Z, BUT LOW CLOUDS WILL RETURN BETWEEN 02-  
05Z WITH BASES FROM OVC012-015 TOPS 027 WILL WILL MOVE BACK INLAND  
THIS EVENING AND REACH KONT BETWEEN 10-12Z.  
 
THE LOW CLOUDS TUESDAY MORNING WILL BE SLOW TO CLEAR BACK TO THE  
COAST TUESDAY AFTERNOON WITH CIGS AT KSAN AND KCRQ THROUGH 21Z.  
THERE WILL ALSO BE POCKETS OF DRIZZLE. VIS AT KONT WILL BE 2-4 MILES  
IN HAZE THROUGH 19Z TUESDAY.  
 
MOUNTAINS/DESERTS...MOSTLY CLEAR WITH UNRESTRICTED THROUGH  
WEDNESDAY.  
 

 
   
MARINE
 
 
NO HAZARDOUS MARINE WEATHER IS EXPECTED THROUGH FRIDAY.  
 

 
   
SGX WATCHES/WARNINGS/ADVISORIES
 
 
CA...NONE.  
PZ...NONE.  

 
 

 
 
PUBLIC...GREGORIA  
AVIATION/MARINE...MOEDE  
 
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