377  
FXUS66 KSEW 140343  
AFDSEW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SEATTLE WA  
843 PM PDT MON AUG 13 2018  
   
SYNOPSIS
 
AN UPPER RIDGE WILL PRODUCE DRY AND WARM WEATHER THE  
NEXT COUPLE OF DAYS. IT WILL ALSO BE SMOKY AT TIMES. ONSHORE FLOW  
WILL DEVELOP LATER WEDNESDAY. THIS WILL COOL HIGHS BACK TO NEAR  
NORMAL THURSDAY AND FRIDAY. HIGH PRESSURE ALOFT WILL REBUILD OVER  
THE AREA NEXT WEEKEND FOR A RETURN WARMER WEATHER.  
 

 
   
SHORT TERM
 
AN UPPER RIDGE WILL BE OVER THE AREA THROUGH  
WEDNESDAY FOR DRY WEATHER. WEAK OFFSHORE FLOW NIGHT AND MORNING  
HOURS WILL TURN LIGHT ONSHORE IN THE AFTERNOON AS A THERMAL  
TROUGH MEANDERS DIURNALLY BETWEEN THE COAST AND THE INTERIOR.  
HIGHS WILL BE ABOVE NORMAL BUT ALL THE SMOKE WILL PUT A DAMPER ON  
TEMPERATURES. HIGHS WILL COOL AROUND 10 DEGREES WEDNESDAY AT THE  
COAST AS ONSHORE FLOW STARTS TO DEVELOP.  
 
THE UPPER RIDGE WILL SHIFT INLAND WEDNESDAY NIGHT AND THURSDAY  
WITH A WEAK UPPER TROUGH MOVING TO THE COAST. THERE WILL BE A  
CORRESPONDING INCREASE IN LOW LEVEL ONSHORE FLOW. A MARINE PUSH  
WILL BRING SOME LOW CLOUDS THURSDAY MORNING AND COOL HIGHS BACK  
TO NEAR NORMAL FOR THE INTERIOR ON THURSDAY.  
 
SPEAKING OF SMOKE...SMOKE FROM FIRES TO THE NORTH AND EAST SHOULD  
CONTINUE TO AFFECT THE REGION THROUGH AT LEAST TUESDAY WITH  
VISIBILITIES REDUCED AT TIMES. THERE COULD ALSO BE AIR QUALITY  
CONCERNS ON TUESDAY AND PERHAPS INTO WEDNESDAY. SCHNEIDER  
   
LONG TERM...PREVIOUS DISCUSSION
 
MODELS REMAIN CONSISTENT WITH  
A WEAK UPPER LEVEL TROUGH MOVING THROUGH THE AREA THURSDAY BRINGING  
TEMPERATURES BACK DOWN TO NEAR NORMAL WITH MID TO UPPER 70S  
EXPECTED IN THE INTERIOR LOWLANDS....MID TO UPPER 60S ALONG THE  
COAST. THERE LOOKS TO BE A LITTLE BIT OF LINGERING INFLUENCE FROM  
THIS SYSTEM ON TEMPS INTO FRIDAY AS HIGHS DO NOT LOOK TO CHANGE  
MUCH.  
 
LATE FRIDAY AFTERNOON WILL SEE UPPER LEVEL RIDGING INTENSIFYING OVER  
THE PACIFIC AND AS SUCH...THIS FEATURE'S INFLUENCE WILL MAKE ITS WAY  
INTO W WA...SO...OF COURSE...THIS MEANS A RETURN TO WARMING  
CONDITIONS AND YET ANOTHER POTENTIAL RUN AT 90 DEGREES. SMR  
 

 
   
AVIATION
 
AN UPPER RIDGE WILL BE OVER THE AREA TONIGHT AND  
TUESDAY WITH NORTHERLY FLOW ALOFT BECOMING EASTERLY. AT THE  
SURFACE, LIGHT OFFSHORE FLOW TONIGHT AND TUESDAY MORNING WILL  
BECOME LIGHT ONSHORE TUESDAY AFTERNOON AS A WEAK THERMAL TROUGH  
ALONG THE COAST SHIFTS OVER THE INTERIOR. THE AIR MASS IS DRY AND  
STABLE. SMOKE WILL CONTINUE TO COVER THE AREA WITH VISIBILITIES  
3-5 MILES AT TIMES. THERE MIGHT BE SOME PATCHY LOW CLOUDS AND FOG  
TUESDAY MORNING BUT IT SHOULD BE PRETTY LIMITED IF THERE IS ANY AT  
ALL.  
 
KSEA...CLEAR. VISIBILITIES 3-5 MILES IN SMOKE AT TIMES. CEILINGS  
3500-4000 FEET ARE POSSIBLE AT TIMES FROM THICKER SMOKE.  
NORTHERLY WIND 5-10 KNOTS. SCHNEIDER  
 

 
   
MARINE
 
A WEAK THERMAL TROUGH WILL DIURNALLY MEANDER FROM THE  
COAST TO THE INLAND WATERS THROUGH EARLY WEDNESDAY WITH LIGHT  
OFFSHORE FLOW NIGHT AND MORNING HOURS AND WEAK ONSHORE FLOW IN THE  
AFTERNOON. MARGINAL SMALL CRAFT ADVISORY STRENGTH NORTHWEST WINDS  
FOR THE INNER COASTAL WATERS SHOULD EASE THIS EVENING.  
 
STRONGER ONSHORE FLOW WILL DEVELOP LATER WEDNESDAY AND CONTINUE  
THROUGH SATURDAY. SMALL CRAFT ADVISORY STRENGTH WEST WINDS ARE  
LIKELY EACH NIGHT FOR THE CENTRAL AND EASTERN STRAIT OF JUAN DE  
FUCA. THERE WILL ALSO BE SMALL CRAFT ADVISORY STRENGTH NORTHWEST  
WINDS AT TIMES FOR THE OUTER COASTAL WATERS. SCHNEIDER  
 

 
   
FIRE WEATHER
 
THE MID-LEVELS (850-700 MB LAYER) WILL BECOME DRY  
AND UNSTABLE OVER THE CASCADES ON TUESDAY PM. FORECAST MODELS POINT  
TO DEVELOPMENT OF AN AREA OF MID-LEVEL HAINES 6 CONDITIONS OVER THE  
CASCADES. HOWEVER, THE THICK REGIONAL SCALE SMOKE --- WHICH  
MODELS DO NOT ACCOUNT FOR --- WILL KEEP THE NEAR-SURFACE AIR MASS  
MORE STABLE. WILL THEREFORE USE DISCRETION AND AVOID ISSUANCE OF A  
RED FLAG WARNING. HOWEVER IF THE SMOKE UNEXPECTEDLY CLEARS OUT  
AND SOLAR INSOLATION PICKS UP ON TUESDAY AFTERNOON, EXISTING FIRES  
COULD EASILY RESPOND TO THE DRY AND UNSTABLE MID-LEVEL AIR MASS.  
HANER  
 

 
   
SEW WATCHES/WARNINGS/ADVISORIES
 
 
WA...NONE.  
PZ...SMALL CRAFT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR COASTAL  
WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10 NM-  
COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER OUT  
10 NM.  
 

 
 

 
 
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