947  
FXUS66 KSGX 201113 CCA  
AFDSGX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN DIEGO CA  
412 AM PDT SUN MAY 20 2018  
 
CORRECTED TO ADD BEACHES SECTION  
   
SYNOPSIS
 
 
A TROUGH ALONG THE WEST COAST AND A COASTAL EDDY WILL CONTINUE  
COOL WEATHER TODAY WITH EXTENSIVE NIGHT AND MORNING LOW CLOUDS  
ALONG AND WEST OF THE MOUNTAINS. SUNNY SKIES WILL CONTINUE OVER  
THE MOUNTAINS AND DESERTS WITH GUSTY WEST WINDS AT TIMES. ON  
MONDAY AND TUESDAY A DEEPER LOW PRESSURE SYSTEM WILL BRING  
ADDITIONAL COOLING AND A CHANCE FOR AFTERNOON SHOWERS AND  
THUNDERSTORMS OVER THE MOUNTAINS AND HIGH DESERTS. IT WILL BE DRY  
AND A LITTLE WARMER WEDNESDAY THROUGH FRIDAY.  
 

 
   
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
 
 
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO  
COUNTIES...  
 
EXTENSIVE LOW CLOUDS AGAIN THIS MORNING GIVEN A DEEP MARINE LAYER  
AND ONSHORE FLOW. CLOUDS WILL BE SLOW TO CLEAR AGAIN TODAY WITH  
PARTLY TO MOSTLY CLOUDY CONDITIONS LIKELY NEAR THE COAST MOST OF  
THE DAY. TEMPERATURES WILL AGAIN BE ON THE COOL SIDE EXCEPT NEAR  
THE COAST WHICH WILL ACTUALLY BE NEAR NORMAL.  
 
ON MONDAY AN ANOMALOUSLY COLD UPPER LOW PRESSURE AREA WILL DROP  
INTO THE MOJAVE DESERT AND LINGER THROUGH TUESDAY SLOWLY MOVING  
NE. THIS WILL HELP TO INCREASE THE ONSHORE FLOW AND BRING GUSTY  
WINDS TO THE MOUNTAINS AND DESERTS WITH SOME BLOWING DUST/SAND  
POSSIBLE IN THE LOWER DESERTS. AT THIS TIME WINDS ARE LIKELY TO BE  
MARGINAL FOR A WIND ADVISORY WITH OCCASIONAL GUSTS OF 45 MPH  
MAINLY IN THE RIVERSIDE AND SAN DIEGO COUNTY MOUNTAINS AND  
DESERTS.  
 
PROXIMITY TO THE UPPER LOW WILL BRING ENOUGH FORCING AND  
INSTABILITY WITH A NARROW RIBBON OF MID LEVEL MOISTURE TO GENERATE  
SCATTERED SHOWERS AND PERHAPS A FEW THUNDERSTORMS OVER THE  
RIVERSIDE AND SAN BERNARDINO COUNTY MOUNTAINS AND THE MOJAVE  
DESERT PORTION OF SAN BERNARDINO COUNTY. WITH MODEST MOISTURE  
PARAMETERS ANY THUNDERSTORMS THAT DO FORM COULD BE CAPABLE OF  
GUSTY DOWNDRAFT WINDS AND DRY LIGHTNING. POPS WERE INCREASED A BIT  
WITH THIS FORECAST MAINLY OVER THE SAN BERNARDINO MOUNTAINS ON  
MONDAY.  
 
WEAK RIDGING IS LIKELY TO DEVELOP WEDNESDAY THROUGH FRIDAY WITH  
SOME WARMER WEATHER FOR INLAND LOCATIONS, MEANWHILE THE MARINE  
LAYER SHOULD RETREAT A BIT WITH LOW CLOUDS STAYING A LITTLE CLOSER  
TO THE COAST THAN THE LAST SEVERAL DAYS.  
 
THE LATEST MEDIUM RANGE MODELS ARE TRENDING WITH A LITTLE BETTER  
CONSENSUS REGARDING THE POTENTIAL FOR ANOTHER ANOMALOUS UPPER  
LOW. THE LATEST TRENDS LOOK TO SHIFT THE TRACK OF THE UPPER LOW  
FURTHER NORTH AGAIN MORE OVER NORCAL WITH A DRIER FLOW OVER SOCAL.  
EVEN WITH THIS PATTERN WE SHOULD EXPECT A DEEPER MARINE LAYER AT  
THE COAST AND A MORE FAVORABLE PATTERN FOR THE POTENTIAL FOR  
STRONG WINDS.  
 

 
   
AVIATION
 
 
200905Z...COAST/VALLEYS...WIDESPREAD OVC LOW CLOUDS COVER THE AREAS  
WEST OF THE MOUNTAINS AGAIN THIS MORNING. BASES ARE 1500-2500 FT MSL  
WITH TOPS TO 3000 FT MSL. HIGHER TERRAIN WILL BE OBSCURED AT TIMES,  
WITH AREAS OF VIS 1-3 MILES AND LOCALLY 1 MILE OR LESS WHERE CLOUDS  
AND TERRAIN INTERSECT. SLOW CLEARING WILL BEGIN INLAND AFTER 16Z,  
WITH ONLY PARTIAL CLEARING WITHIN 15 MILES OF THE COAST. LOW CLOUDS  
INCREASING IN COVERAGE AGAIN THIS EVENING WITH SIMILAR BASES AND  
TOPS.  
 
MOUNTAINS/DESERTS...MOSTLY CLEAR SKIES WITH UNRESTRICTED VIS THROUGH  
THIS EVENING.  
 

 
   
MARINE
 
 
NO HAZARDOUS MARINE CONDITIONS ARE EXPECTED THROUGH THURSDAY.  
 

 
   
BEACHES
 
 
A LONG PERIOD SOUTH-SOUTHWEST SWELL FROM 200 DEGREES WILL BEGIN TO  
BUILD LATE ON MONDAY, PEAKING TUESDAY AFTERNOON INTO WEDNESDAY AT 3-  
4 FT/17-19 SEC. THE SWELL WILL VERY SLOWLY LOWER LATE THURSDAY AND  
FRIDAY. THIS WILL LIKELY RESULT IN A PERIOD OF HIGH SURF ALONG  
SOUTHWEST FACING BEACHES TUESDAY INTO THURSDAY. STRONG RIP AND  
LONGSHORE CURRENTS AND MINOR BEACH EROSION ARE ALSO POSSIBLE DURING  
THIS PERIOD.  
 

 
   
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...BROTHERTON  
AVIATION/MARINE...PG  
 
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