790  
FXUS66 KSEW 222203  
AFDSEW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SEATTLE WA  
303 PM PDT FRI JUN 22 2018  
   
SYNOPSIS
 
AN UPPER TROUGH WILL MOVE INLAND TONIGHT. A PUGET  
SOUND CONVERGENCE ZONE IS LIKELY TONIGHT. AN UPPER RIDGE WILL  
BRING SUNNY AND SOMEWHAT WARMER WEATHER THIS WEEKEND. AN UPPER  
TROUGH WILL ARRIVE MONDAY FOR A RETURN TO SLIGHTLY COOLER WEATHER.  
 

 
   
SHORT TERM
 
A PUGET SOUND CONVERGENCE ZONE IS POSSIBLE TONIGHT  
AS AN UPPER TROUGH MOVES INLAND. AN UPPER RIDGE WILL MOVE OVER  
THE AREA ON SATURDAY FOR DRY WEATHER. MORNING CLOUDS SHOULD GIVE  
WAY TO SOME AFTERNOON SUNSHINE AND HIGHS WILL CREEP UP A FEW  
DEGREES. THE UPPER RIDGE WILL SHIFT INLAND ON SUNDAY WITH AN UPPER  
TROUGH OFFSHORE AND AN APPROACHING WEAK FRONTAL SYSTEM. IT SHOULD  
BE A MOSTLY SUNNY DAY WITH HIGHS WARMING A FEW MORE DEGREES. THE  
AFOREMENTIONED FRONTAL SYSTEM WILL MOVE THROUGH THE AREA SUNDAY  
NIGHT. IT WILL BE WEAKENING AS IT MOVES ONSHORE AND RAIN WILL BE  
SPOTTY. A FEW SHOWERS WILL LINGER INTO MONDAY AS AN UPPER TROUGH  
SETTLES OVER THE AREA. ONSHORE FLOW WILL KEEP SKIES MOSTLY CLOUDY  
AND HIGHS WILL COOL 10-15 DEGREES. SCHNEIDER  
   
LONG TERM
 
WEAK HIGH PRESSURE ALOFT WILL MOVE OVER THE AREA  
TUESDAY AND WEDNESDAY FOLLOWED BY A WEAK UPPER TROUGH THURSDAY AND  
FRIDAY. ONSHORE FLOW WILL CONTINUE THROUGH THE PERIOD. NIGHT AND  
MORNING CLOUDS ARE LIKELY EACH DAY WITH SOME AFTERNOON SUNSHINE.  
TEMPERATURES WILL BE NEAR OR SLIGHTLY ABOVE NORMAL. ISOLATED  
SHOWERS ARE POSSIBLE AT TIMES BUT NO ORGANIZED SYSTEMS AREA  
EXPECTED. THE GENERAL TREND WILL BE FOR SHOWERS TO INCREASE LATE  
IN THE WEEK. THE GFS IS WETTER THAN THE ECMWF AND GEM THURSDAY  
AND FRIDAY. THE FORECAST LEANS MORE TO THE DRIER ECMWF FOR NOW.  
SCHNEIDER  
 

 
   
AVIATION
 
A WEAK UPPER LEVEL TROUGH WILL MOVE EAST OF THE REGION  
TONIGHT, AND AN UPPER LEVEL RIDGE WILL BUILD OFFSHORE SATURDAY. FLOW  
ALOFT WILL BE NORTHWESTERLY. MODERATE TO STRONG LOW LEVEL ONSHORE  
FLOW WILL CONTINUE TONIGHT AND SATURDAY. THE AIR MASS IS STABLE WITH  
LOW LEVEL MOISTURE. RADAR SHOWS ISOLATED LIGHT SHOWERS WHICH WILL  
CONTINUE INTO TONIGHT. A CONVERGENCE ZONE IS FORECAST TO FORM OVER  
MAINLY KING COUNTY TONIGHT.  
 
CEILINGS THIS AFTERNOON ARE MOSTLY AROUND 3.5K FT WITH CLEAR AREAS  
MAINLY SOUTH PART. MARINE STRATUS WILL INCREASE LATER TONIGHT WITH  
CEILINGS FORMING AGAIN AND FALLING BACK TO 1-2K FT. SCATTERED  
SHOWERS ARE FORECAST, MAINLY IN THE MOUNTAINS AND IN A CONVERGENCE  
ZONE.  
 
KSEA...DISCUSSION ABOVE APPLIES. MODEL SOLUTIONS HAVE A CONVERGENCE  
ZONE OVER SOUTH KING COUNTY TONIGHT SO WILL KEEP SHOWERS IN THE TAF.  
SOUTHWEST WIND 4-8 KT THOUGH THERE COULD BE A FEW HOURS OF NORTHERLY  
WIND THIS EVENING ASSOCIATED WITH THE CONVERGENCE ZONE. THERE WILL  
BE GOOD VFR SATURDAY AFTERNOON. CHB  
 

 
   
MARINE
 
ONSHORE FLOW WILL CONTINUE THROUGH THE PERIOD. WESTERLIES  
WILL CONTINUE IN THE STRAIT OF JUAN DE FUCA--RISING TO AT LEAST 20-  
30 KT EACH EVENING, BUT POSSIBLY REACHING GALE FORCE FOR A FEW  
HOURS. FORECAST GRADIENT TONIGHT FOR KUIL-KBLI IS MORE THAN 3 MB SO  
HAVE ISSUED A GALE WARNING FOR 25-35 KT TONIGHT. CHB  
 

 
   
SEW WATCHES/WARNINGS/ADVISORIES
 
 
WA...NONE.  
PZ...GALE WARNING UNTIL 5 AM PDT SATURDAY FOR CENTRAL U.S. WATERS  
STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS STRAIT OF  
JUAN DE FUCA.  
 

 
 

 
 
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