652  
FXUS66 KLOX 120359  
AFDLOX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LOS ANGELES/OXNARD CA  
859 PM PDT SUN APR 11 2021  
   
SYNOPSIS
 
11/843 PM.  
 
CLOUDS AND FOG WILL BECOME MORE WIDESPREAD THROUGH MID WEEK,  
REACHING THE COASTAL SLOPES BY TUESDAY MORNING. LATE NIGHT  
THROUGH MORNING DRIZZLE OR VERY LIGHT RAIN IS POSSIBLE FROM THE  
COAST TO THE COASTAL SLOPES OF LOS ANGELES AND VENTURA COUNTIES  
MONDAY NIGHT THROUGH WEDNESDAY. THERE WILL BE A COOLING TREND  
THROUGH MID WEEK, WITH SLIGHT WARMING BY FRIDAY AND SATURDAY.  
 

 
   
SHORT TERM (SUN-WED)
 
11/858 PM.  
 
UPPER LEVEL TROUGH OF LOW PRESSURE OVER THE GREAT BASIN TONIGHT  
THOROUGH MONDAY WILL FURTHER DEEPEN INTO TUESDAY. THIS WILL  
GENERATE A STRENGTHENING ONSHORE FLOW PATTERN AND DEEPENING OF THE  
MARINE LAYER THROUGH TUESDAY. PRESSURE GRADIENTS ALREADY STARTING  
TO TREND ONSHORE THIS EVENING, WITH LAX-DAGGETT AT +5.3 MB AT  
8 PM, AND IS EXPECTED TO INCREASE TO AROUND +8 MB BY MONDAY  
AFTERNOON, AND POSSIBLY AS HIGH AS +10 MB BY TUESDAY AFTERNOON.  
CURRENT SATELLITE IMAGERY SHOWING LOW CLOUDS AND FOG RAPIDLY  
DEVELOPING THIS EVENING ACROSS THE LA COUNTY COAST AND CENTRAL  
COAST. THE ONSHORE TRENDS COMBINED WITH A STRENGTHENING EDDY  
CIRCULATION WILL BRING LOW CLOUDS AND FOG INTO MANY COASTAL/VALLEY  
AREAS OVERNIGHT INTO MONDAY MORNING. ANOTHER ITEM OF NOTE THIS  
EVENING IS THE LINGERING SUNDOWNER WINDS ACROSS THE WESTERN  
PORTIONS OF THE SANTA BARBARA SOUTH COAST AND ADJACENT SANTA YNEZ  
MOUNTAINS, WHERE LOCALIZED WIND GUSTS TO 50 MPH HAVE BEEN OBSERVED  
NEAR GAVIOTA. WIND ADVISORIES ARE IN EFFECT TONIGHT FOR THIS  
AREA, BUT SHOULD SEE A STEADY DECREASE IN WINDS OVERNIGHT AS THE  
NORTHWEST PRESSURE GRADIENT RELAXES.  
 
THE STRONG ONSHORE FLOW PATTERN AND INCREASED MARINE LAYER  
INFLUENCE WILL BRING WIDESPREAD COOLING TO THE REGION ON MONDAY,  
WITH FURTHER COOLING INTO TUESDAY/WEDNESDAY. LOW CLOUDS WILL  
LIKELY LINGER ACROSS PORTIONS OF THE COAST ON MONDAY AFTERNOON,  
AND THEN RAPIDLY EXPAND INLAND ON MONDAY EVENING, PUSHING INTO  
THE LOWER COASTAL SLOPES OVERNIGHT AS THE MARINE LAYER RAPIDLY  
DEEPENS TO 4000 TO 5000 FEET. THIS RAPID DEEPENING OF THE MARINE  
LAYER MONDAY NIGHT AND TUESDAY MORNING WILL LIKELY BRING AREAS OF  
DRIZZLE, AND POSSIBLY LIGHT MEASURABLE RAINFALL (ESPECIALLY ACROSS  
THE FOOTHILLS AND COASTAL SLOPES OF LA COUNTY). GUSTY ONSHORE  
WINDS WILL ALSO BE OCCURING THE NEXT FEW DAYS ACROSS THE MOUNTAINS  
AND DESERTS, LIKELY PEAKING ON TUESDAY AND WEDNESDAY WHEN GUSTS  
OF 35 TO 50 MPH WILL BE LIKELY, WITH ISOLATED GUSTS AS HIGH AS 60  
MPH IN THE FOOTHILLS OF THE ANTELOPE VALLEY. AS A RESULT, WIND  
ADVISORIES WILL LIKELY BE NEEDED BY TUESDAY FOR PORTIONS OF THE  
MOUNTAINS AND ANTELOPE VALLEY.  
 
*** FROM PREVIOUS DISCUSSION ***  
 
SIMILAR SCENARIO FOR WEDNESDAY. GRADIENTS A SKOSH WEAKER BUT WITH  
THE UPPER LOW STILL PARKED OVER UT (DUE TO ANOTHER UPPER LOW OVER  
THE NORTHEAST) EXPECT ANOTHER COOL, DRIZZLY, CLOUDY DAY MOST AREAS  
WITH GUSTY WINDS IN THE ANTELOPE VALLEY.  
   
LONG TERM (THU-SUN)
 
11/121 PM.  
 
THE TWO-PRONGED UPPER LOW PATTERN ACROSS THE US WILL FINALLY START  
TO SHIFT EAST THURSDAY BUT LIKELY NOT BEFORE ONE MORE DAY OF A  
DEEP MARINE LAYER. CLOUDS SHOULD CLEAR EARLIER THAN WEDNESDAY AS  
ONSHORE FLOW WEAKENS AND THERE WILL BE SOME RECOVERY IN  
TEMPERATURES BUT STILL MOSTLY BELOW NORMAL.  
 
SOME WARMING EXPECTED FOR NEXT WEEKEND BUT NOT CONFIDENT TEMPS  
WILL BE AS WARM AT THE NBM IS SUGGESTING DUE TO AT LEAST SOME  
MODEL SOLUTIONS KEEPING WEAK TROUGHING ACROSS THE AREA THROUGH  
LATE SUNDAY. EARLIER GFS SOLUTIONS HAD SOME LIGHT OFFSHORE FLOW  
DEVELOPING BY SUNDAY BUT TODAY'S MODEL IS STILL ONSHORE. THE ECMWF  
IS MORE OFFSHORE AND NOT AS STRONG WITH THE TROUGH. WILL HAVE TO  
WAIT PROBABLY A FEW MORE DAYS AT LEAST TO SEE A CLEAR WINNER HERE.  
 

 
   
AVIATION
 
12/0054Z.  
 
AT 2357Z AT KLAX...THE MARINE LAYER WAS AROUND 1300 FEET DEEP.  
THE TOP OF THE INVERSION WAS 3200 FEET WITH A TEMPERATURE OF 18  
DEGREES C.  
 
HIGH CONFIDENCE IN DESERT TAFS. MODERATE TO LOW CONFIDENCE IN  
VALLEY AND COASTAL TAFS DUE TO INCREASING ONSHORE FLOW AND  
DEEPENING MARINE LAYER. LOW CONFIDENCE IN THE CLEARING TIMES FOR  
THE L.A. COASTAL AREAS, WITH CLOUDS POSSIBLY STICKING AROUND  
1-3 HRS LATER. GENERALLY EXPECTING MVFR & IFR CONDITIONS WITH  
MARINE LAYER CLOUDS, BUT THERE IS A 20% CHANCE FOR LIFR CONDITIONS  
FOR THE VALLEYS AND COASTS AT KOXR AND NORTHWARD.  
 
KLAX...HIGH CONFIDENCE IN THE 00Z TAF THROUGH 06Z, THEN MODERATE  
TO LOW CONFIDENCE WITH LOW CLOUDS MVFR DEVELOPING TONIGHT. THERE  
IS A 30% CHANCE FOR ANY EAST WIND COMPONENT TO EXCEED 9 KT LATER  
TONIGHT FROM 08Z TO 12Z.  
 
KBUR...HIGH CONFIDENCE IN THE 00Z TAF THROUGH 08Z, THEN MODERATE  
TO LOW CONFIDENCE. THERE IS A 20% CHANCE FOR LIFR CONDITIONS.  
 

 
   
MARINE
 
11/839 PM.  
 
ACROSS THE OUTER WATERS...GALE WARNINGS HAVE BEEN CONVERTED TO  
SMALL CRAFT ADVISORIES THIS EVENING. SMALL CRAFT ADVISORIES WILL  
LIKELY PERSIST THROUGH AT LEAST MONDAY EVENING, AND POSSIBLY INTO  
TUESDAY EVENING FOR ZONE 670. SEAS WILL ALSO APPROACH SCA LEVEL  
THROUGH TONIGHT.  
 
ACROSS THE NEARSHORE WATERS OF THE CENTRAL COAST...WINDS WILL  
LIKELY REMAIN BELOW SMALL CRAFT ADVISORY LEVELS FOR THE NEXT FEW  
DAYS.  
 
ACROSS THE INNER WATERS SOUTH OF POINT CONCEPTION...WINDS HAVE  
DIMINISHED BELOW SMALL CRAFT ADVISORY LEVELS. AN EDDY CIRCULATION  
WILL STRENGTHEN OVERNIGHT INTO MONDAY MORNING.  
 

 
   
LOX WATCHES/WARNINGS/ADVISORIES
 
 
CA...WIND ADVISORY IN EFFECT UNTIL MIDNIGHT PDT TONIGHT FOR ZONES  
39-52. (SEE LAXNPWLOX).  
PZ...SMALL CRAFT ADVISORY IN EFFECT UNTIL 9 PM PDT THIS EVENING  
FOR ZONES 645-650. (SEE LAXMWWLOX).  
SMALL CRAFT ADVISORY IN EFFECT UNTIL 9 PM PDT TUESDAY FOR  
ZONE 670. (SEE LAXMWWLOX).  
SMALL CRAFT ADVISORY IN EFFECT UNTIL 9 PM PDT MONDAY FOR  
ZONES 673-676. (SEE LAXMWWLOX).  
 

 
 
.HAZARD POTENTIAL OUTLOOK (WED-SUN).  
 
ADVISORY LEVEL WEST WINDS ARE POSSIBLE ACROSS THE ANTELOPE VALLEY  
WEDNESDAY.  
 

 
 

 
 
PUBLIC...GOMBERG/MW  
AVIATION...PHILLIPS/SWEET  
MARINE...GOMBERG/SWEET  
SYNOPSIS...GOMBERG  
 
WEATHER.GOV/LOSANGELES  
 
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