163  
FXUS66 KSGX 120449 AAA  
AFDSGX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN DIEGO CA  
943 PM PDT SUN APR 11 2021  
   
SYNOPSIS
 
 
COOLING WILL INTENSIFY MONDAY AND TUESDAY IN RESPONSE TO A LOW  
PRESSURE SYSTEM DEVELOPING OVER THE NORTHERN GREAT BASIN. THIS WILL  
ENHANCE ONSHORE FLOW ACROSS THE REGION, BRINGING GUSTY WINDS TO  
DESERT SLOPES AND PASSES MONDAY THROUGH WEDNESDAY (STRONGEST  
TUESDAY), AND A DEEPER MARINE LAYER. THE LATTER SHOULD BE SUFFICIENT  
TO GENERATE SOME SPRINKLES ACROSS THE COASTAL BASIN MONDAY NIGHT  
INTO EARLY TUESDAY MORNING, AND POSSIBLY AGAIN TUESDAY NIGHT, WITH  
MINIMAL ACCUMULATIONS EXPECTED. THURSDAY WILL SEE US RETURN TO A  
WARMING TREND THAT WILL CONTINUE INTO THE WEEKEND, WITH SHALLOWER  
MARINE LAYER CLOUDS EACH NIGHT/MORNING AT THE COAST.  
 

 
   
DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE
 
 
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO  
COUNTIES...  
 
EVENING UPDATE:  
 
THE ONSHORE GRADIENTS ARE SLOWLY INCREASING THIS EVENING AND A  
HEALTHY CATALINA EDDY HAS HELPED TO DEEPEN THE MARINE LAYER AND  
PRODUCE ABUNDANT COASTAL STRATUS, NOW QUICKLY PUSHING INTO THE  
WESTERN VALLEYS THIS EVENING. THE FORECAST WAS UPDATED EARLIER TO  
SPREAD THE CLOUDS FASTER AND FURTHER INLAND THROUGH THE REMAINDER OF  
THE NIGHT. NO OTHER UPDATES WERE NEEDED AT THIS TIME.  
 
PREVIOUS DISCUSSION, ISSUED AT 137 PM PDT:  
 
HIGH CLOUDS ARE ABUNDANT TODAY, SHIELDING US FROM BRIGHTER SKIES AND  
KEEPING TEMPERATURES A LITTLE MORE IN CHECK COMPARED TO PREVIOUS  
DAYS. IT'S RELATIVELY MILD NONETHELESS, WITH INLAND AREAS  
(ESPECIALLY THE MOUNTAINS AND DESERTS) STILL A FEW DEGREES ABOVE  
NORMAL. LOW CLOUDS WILL AGAIN FILL THE COASTAL BASIN TONIGHT,  
EXTENDING FAR INTO THE VALLEYS AS A COASTAL EDDY AND TIGHTENING  
ONSHORE PRESSURE GRADIENTS FORCE SOME DEEPENING.  
 
WITH A LOW PRESSURE SYSTEM DROPPING SOUTHWARD TOWARD THE NORTHERN  
GREAT BASIN MONDAY INTO TUESDAY, BELOW NORMAL TEMPERATURES WILL  
FINALLY MAKE A RETURN. GUSTY WEST WINDS WILL FOLLOW SUIT, IMPACTING  
DESERT SLOPES AND EAST-WEST FACING PASSES THROUGH WEDNESDAY, AND  
PEAKING ON TUESDAY WHEN THEY'LL LIKELY REACH ADVISORY LEVELS WITH  
GUSTS 35 TO 50 MPH, LOCALLY HIGHER.  
 
BY MONDAY NIGHT, THE MARINE LAYER WILL HAVE DEEPENED ENOUGH TO ALLOW  
FOR PATCHY DRIZZLE OR BRIEF LIGHT SHOWERS ACROSS MUCH OF THE COASTAL  
BASIN AND INTO THE WINDWARD MOUNTAIN SLOPES. ACCUMULATIONS, IF ANY,  
WILL BE LIGHT AND MEASURED IN HUNDREDTHS OF AN INCH, TAPERING OFF IN  
THE MORNING. A SIMILAR SCENARIO MAY PLAY OUT TUESDAY NIGHT INTO  
EARLY WEDNESDAY MORNING. TUESDAY AND WEDNESDAY WILL BE SIMILARLY  
COOL, WITH HIGHS THAT WILL STRUGGLE TO REACH 70 ANYWHERE OUTSIDE OF  
THE DESERTS.  
 
AND THAT, FOLKS, WILL BE THE EXTENT OF THIS TEASER. IT WILL BE A  
WELCOME CHANGE FOR MANY, BRINGING PLEASANTLY COOL TEMPERATURES FOR  
HIKING, THOUGH CERTAINLY NOT IDEAL BEACH WEATHER. OUR VEGETATION  
WOULD CERTAINLY APPRECIATE SOME MEANINGFUL PRECIPITATION AS WE INCH  
CLOSER TO THE CLIMATOLOGICAL END TO OUR RAINY SEASON (AND ALSO AN  
ALMOST GUARANTEED EARLY START TO HIGH FIRE SEASON), BUT THAT'S NOT  
ON THE TABLE AS IT STANDS. AS THE GREAT BASIN LOW DISSIPATES, ZONAL  
FLOW WILL GRADUALLY TRANSITION TO WEAK RIDING AS WE NEAR THE  
WEEKEND. TEMPERATURES WILL BEGIN TO WARM STARTING THURSDAY, AND THE  
WARMING TREND WILL LAST THROUGH AT LEAST SUNDAY, BY WHICH TIME WE  
SHOULD RETURN TO WARMER THAN AVERAGE CONDITIONS AS HIGHS IN THE 80'S  
MAKE A COMEBACK TO THE INTERIOR. COASTAL LOW CLOUDS WILL CONTINUE  
EACH NIGHT AND MORNING, BUT WILL BE CONSIDERABLY SHALLOWER DURING  
THE LATTER HALF OF THE WEEK.  
 

 
   
AVIATION
 
 
120405Z...COAST/VALLEYS...LOW CLOUDS INCREASING IN COVERAGE AND  
SPREADING UP TO 20 MILES INLAND OVERNIGHT, LIKELY REACHING KONT  
AROUND 09Z. EXPECT CIGS 1200-1800 FT MSL AT COASTAL TAF SITES WITH  
TOPS TO 2200 FT MSL OBSCURING HIGHER TERRAIN. LOCAL VIS 1-3 MILES  
WILL OCCUR IN THE VALLEYS THROUGH 16Z MON. CLEARING FROM INLAND TO  
THE COAST EXPECTED 16Z-19Z MON. OTHERWISE, MOSTLY SCT CLOUDS  
AT/ABOVE 20000 FT MSL THROUGH MON MORNING.  
 
MOUNTAINS/DESERTS...MOSTLY SCT CLOUDS AT/ABOVE 20000 FT MSL WITH  
UNRESTRICTED VIS THROUGH MON MORNING.  
 

 
   
MARINE
 
 
WEST-NORTHWEST WINDS WITH GUSTS TO 20 KNOTS WILL OCCUR EACH  
AFTERNOON AND EVENING IN THE OUTER WATERS THROUGH MONDAY. STRONGEST  
WINDS WILL BE NEAR SAN CLEMENTE ISLAND. OTHERWISE, NO HAZARDOUS  
MARINE WEATHER IS EXPECTED THROUGH FRIDAY.  
 

 
   
SKYWARN
 
 
SKYWARN ACTIVATION IS NOT REQUESTED. HOWEVER WEATHER SPOTTERS ARE  
ENCOURAGED TO REPORT SIGNIFICANT WEATHER CONDITIONS.  
 

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

 
 

 
 
SYNOPSIS/PUBLIC DISCUSSION...RODRIGUEZ/JMB  
AVIATION/MARINE...PG  
 
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