743  
FXUS66 KSEW 211631  
AFDSEW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SEATTLE WA  
931 AM PDT SAT SEP 21 2019  
   
SYNOPSIS
 
UPPER LEVEL RIDGE OVER THE AREA WILL SHIFT EAST LATER  
TODAY. A COLD FRONT WILL SPREAD RAIN THROUGH THE AREA SUNDAY  
MORNING. A WEAKER SYSTEM WILL MOVE THROUGH MONDAY NIGHT. AFTER A  
BREAK A COOL UPPER LEVEL TROUGH WILL ARRIVE LATE IN THE WEEK  
KEEPING UNSETTLED WEATHER IN THE FORECAST.  
 

 
   
SHORT TERM /TODAY THROUGH MONDAY/
 
SATELLITE IMAGERY SHOWS AREAS  
OF LOW CLOUDS OVER WESTERN WASHINGTON THIS MORNING WITH PLENTY OF  
BREAKS ALREADY SHOWING UP IN THE IMAGERY. TEMPERATURES AT 9 AM/16Z  
WERE IN THE MID 50S TO LOWER 60S.  
 
LOOKS LIKE A SPLIT FOR THE WEEKEND WEATHER WISE WITH A DRY DAY  
TODAY AND A WET DAY ON SUNDAY. UPPER LEVEL RIDGE OVER THE AREA  
THIS MORNING SHIFTING EAST THIS AFTERNOON AND EVENING. LIGHT FLOW  
IN THE LOWER LEVELS COMBINED WITH A SHALLOW MARINE LAYER THIS  
MORNING WILL RESULT IN THE LOWER CLOUD COVER SCATTERING OUT THIS  
AFTERNOON. WITH SOME SUNSHINE HIGHS WILL BE NEAR NORMAL, IN THE  
60S AND LOWER 70S.  
 
INCREASING CLOUDS THIS EVENING AS THE COLD FRONT, CURRENTLY BACK  
NEAR 134W, APPROACHES THE AREA. RAIN OUT AHEAD OF THE FRONT  
STARTING ALONG THE COAST AROUND MIDNIGHT WITH THE LEADING EDGE OF  
THE RAIN NEAR THE SEATTLE AREA BY 12Z SUNDAY. LOWS TONIGHT IN THE  
50S.  
 
COLD FRONT MOVING THROUGH WESTERN WASHINGTON SUNDAY MORNING/MIDDAY  
WITH THE UPPER LEVEL TROUGH AXIS RIGHT BEHIND THE FRONT FOR SUNDAY  
AFTERNOON. RAIN CHANGING TO SHOWERS FORECAST ON TRACK FOR SUNDAY.  
HIGHS WILL ONLY BE IN THE LOWER TO MID 60S.  
 
UPPER LEVEL RIDGE TRYING TO REBUILD SUNDAY NIGHT INTO MONDAY WITH  
A WEAK SYSTEM MOVING OVER THE TOP OF THE RIDGE INTO WESTERN  
WASHINGTON LATE MONDAY. THE RIDGE WILL TAKE A TOLL ON THE SYSTEM  
WITH THE BEST CHANCE FOR LIGHT RAIN OVER THE NORTHERN SECTIONS.  
HIGHS ONCE AGAIN IN THE LOWER TO MID 60S.  
 
WILL INCREASE THE RAIN CHANCES 06Z-12Z SUNDAY. REMAINDER OF THE  
FORECAST UNCHANGED THIS MORNING. FELTON  
   
LONG TERM /TUESDAY THROUGH FRIDAY/
 
PREVIOUS DISCUSSION FOLLOWS. THERE  
ARE HINTS AT A BREAK IN THE ACTION TUESDAY AS A LARGE SCALE  
TROUGH SHIFTS MORE TOWARD THE CENTER OF THE US...THE ECMWF SHOWING  
THIS A BIT BETTER THAN THE CURRENT GFS...BUT MODELS COME BACK IN  
AGREEMENT THAT ANOTHER LARGE SCALE TROUGH WILL BEGIN TO SET UP  
SHOP OVER THE AREA STARTING WEDNESDAY NIGHT WITH A SERIES OF UPPER  
LEVEL LOWS DIPPING DOWN INTO THE AREA AND MAKING FOR A GENERALLY  
WET REMAINDER OF THE WEEK. MODELS DO DISAGREE ON TIMINGS AND PATHS  
OF THESE LOWS HOWEVER...SO A BREAK OR TWO IN THE ACTION IS  
CERTAINLY POSSIBLE. FOR EXAMPLE...THE GFS TRIES TO PUSH AN UPPER  
LEVEL LOW SOUTH OF THE AREA TO THE CA/OR BORDER FRIDAY WHICH WOULD  
MAKE FOR A POTENTIALLY DRY DAY...BUT THE ECMWF KEEPS THE SYSTEM  
FURTHER NORTH CLOSE TO THE WA/OR BORDER WHICH WOULD KEEP THE  
POTENTIAL FOR RAIN GOING. OPTING TO SPLIT THE DIFFERENCE AND THUS  
ADVERTISE A GENERALLY WET PATTERN UNTIL A MORE CONCRETE CONSENSUS  
EMERGES. TEMPS WILL CONTINUE THEIR COOLING TREND THROUGH THIS  
PERIOD. LOWLAND HIGHS WILL START OFF TUESDAY IN THE LOWER TO MID  
60S BUT FALL INTO THE MID TO UPPER 50S THURSDAY WHICH IS COOLER  
THAN WHAT WOULD NORMALLY BE SEEN THIS TIME OF YEAR. SMR  
 

 
   
AVIATION
 
NORTHERLY FLOW ALOFT WILL BECOME MORE WESTERLY AND  
SOUTHWESTERLY TODAY AS AN UPPER LEVEL RIDGE STARTS TO EXIT THE  
AREA, MAKING WAY FOR AN INCOMING UPPER LEVEL TROUGH. CURRENT  
SATELLITE IMAGERY INDICATES AREAS OF PATCHY FOG AND LOW STRATUS  
ACROSS PORTIONS OF THE SOUND, YIELDING LIFR CEILINGS FOR KPWT AND  
KPAE. OTHERWISE, THERE'S A MIXED BAG OF MVFR/IFR CONDITIONS FOR  
OTHER TERMINALS ACROSS THE SOUND, COAST, AND SOUTHWEST INTERIOR.  
ONLY KBLI IS EXPERIENCING VFR CONDITIONS AT THIS HOUR. EXPECT  
GRADUAL IMPROVEMENT OF CONDITIONS THROUGHOUT THE MORNING HOURS TO  
VFR THIS AFTERNOON.  
 
THE NEXT FRONTAL SYSTEM WILL APPROACH WESTERN WASHINGTON TONIGHT  
AND MOVE INLAND DURING THE OVERNIGHT HOURS, BRINING RAIN AND LOWER  
CEILINGS TO THE REGION. EXPECT WINDS TO BE SOUTHERLY AROUND 4 TO  
8 KNOTS TODAY.  
 
KSEA...CURRENT CONDITIONS MVFR. EXPECT STRATUS TO CLEAR BY MIDDAY  
AND IMPROVE TO VFR CONDITIONS BY THIS AFTERNOON. WINDS SOUTHERLY  
4 TO 8 KNOTS. SB  
 

 
   
MARINE
 
LIGHTER ONSHORE FLOW WILL PERSIST THROUGH THE DAY  
TODAY. A FRONTAL SYSTEM WILL THEN MOVE THROUGH THE AREA LATE  
TONIGHT THROUGH SUNDAY. SMALL CRAFT ADVISORY SOUTHERLIES WILL BE  
LIKELY FOR THE COASTAL WATERS AHEAD OF THE FRONT, WITH SMALL CRAFT  
ADVISORY WESTERLIES EXPECTED IN ITS WAKE. SCA LEVEL WESTERLIES  
WILL ALSO BE POSSIBLE IN THE CENTRAL AND EASTERN PORTIONS OF THE  
STRAIT OF JUAN DE FUCA ON SUNDAY NIGHT FOLLOWING THE FRONTAL  
PASSAGE. ANOTHER SYSTEM WILL SLIDE THROUGH THE REGION MONDAY INTO  
MONDAY NIGHT. SB  
 

 
   
HYDROLOGY
 
THE DAILY HYDROLOGY DISCUSSION HAS ENDED UNTIL THE  
START OF THE NEXT RAINY SEASON; IT WILL ONLY BE UPDATED AS NEEDED  
UNTIL THEN.  
 

 
   
SEW WATCHES/WARNINGS/ADVISORIES
 
 
WA...NONE.  
PZ...SMALL CRAFT ADVISORY FROM 2 AM SUNDAY TO 2 AM PDT MONDAY FOR  
COASTAL WATERS FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60  
NM-COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10  
TO 60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE  
SHOALWATER 10 TO 60 NM.  
 
SMALL CRAFT ADVISORY FROM 2 AM TO 8 AM PDT SUNDAY FOR COASTAL  
WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM-COASTAL  
WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10 NM-  
COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER OUT  
10 NM.  
 

 
 

 
 
WWW.WEATHER.GOV/SEATTLE  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab WA Page Main Text Page