976
FXUS66 KSEW 170952
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
252 AM PDT MON AUG 17 2026
SYNOPSIS
A TROUGH WILL MOVE ACROSS THE REGION LATE MONDAY INTO
TUESDAY. A WARMER AND DRIER TREND WILL COMMENCE MID TO LATE
WEEK AS A RIDGE STARTS TO BUILD INTO THE REGION, HOWEVER SHOWER
AND THUNDERSTORM CHANCES INCREASE AGAIN HEADING INTO NEXT WEEKEND
AS THE NEXT SYSTEM APPROACHES THE REGION.
SHORT TERM /TODAY THROUGH WEDNESDAY/
500MB PATTERN REMAINS LARGELY UNCHANGED AS BROAD TROUGHING
CONTINUES OVER THE NE PAC AND RIDGING NOSES INTO THE PNW. LOW-
LEVEL ONSHORE FLOW READILY APPARENT ON SATELLITE AS MARINE
STRATUS ONCE AGAIN STRETCHES FROM THE COASTAL WATERS TO THE
WESTERN WA INTERIOR UNDER MID-HIGH LEVEL CLOUD COVERAGE. IT'LL
BE ANOTHER DAY OF MORNING CLOUDS AFTERNOON SUN ACROSS THE AREA
WITH HIGH TEMPERATURES AROUND SEASONAL AVERAGE. MONDAY'S WEATHER
IS EXPECTED TO BE CARBON COPIES OF BOTH TUESDAY AND
WEDNESDAY'S. GLOBAL DETERMINISTIC MODEL GUIDANCE ARE IN LOCK-
STEP OVER A REX BLOCK CONTINUING OVER THE NE PAC, MAINTAINING A
RATHER STAGNANT PATTERN. MORNING CLOUDS AND AFTERNOON SUN WITH
HIGHS IN THE MID 70S TO LOWER 80S IN THE FORECAST. OVERNIGHT
LOWS WILL BE GENERALLY IN THE 50S.
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
ENSEMBLE GUIDANCE SUGGEST NEAR NORMAL TEMPERATURES AND ONSHORE FLOW
AT THE LOW LEVELS MAINTAINING MORNING CLOUDS WITH AFTERNOON CLEARING
FOR THE MIDWEEK TIME PERIOD. DRY CONDITIONS LIKELY CONTINUE THROUGH
THE END OF THE WEEK. AROUND FRIDAY, EXPECT THAT THE RIDGE OVER THE
ROCKIES/GREAT BASIN AMPLIFIES WITH THE NEXT UPPER TROUGH APPROACHING
THE WEST COAST. THIS WILL LIKELY BRING A SHIFT IN THE PATTERN WITH
THE POTENTIAL FOR PRECIPITATION AND COOLER TEMPERATURES, ALONG WITH
THUNDERSTORM CHANCES INCREASING INTO SATURDAY.
AVIATION
A RETROGRADING UPPER TROUGH WILL MAINTAIN DIFFLUENT
FLOW OVER WESTERN WASHINGTON THIS MORNING. MARINE STRATUS WITH LIFR
CIGS CONTINUES TO INCH ITS WAY EASTWARD ACROSS THE AREA THIS
MORNING, AND IS EXPECTED TO REACH THE METRO AREA BY AROUND SUNRISE.
SOME LOCATIONS ARE BEGINNING TO SEE IMPACTS TO VISIBILITY AS THE
STRATUS LOWERS TO GROUND LEVEL. MODELS ARE INDICATING A FAIRLY RAPID
CLEAR OUT THIS MORNING, WITH MOST TERMINALS CLEARING OUT BY AROUND
17-19Z, WITH AREAS ALONG THE COAST AND STRAIT OF JUAN DE FUCA BEING
THE LAST TO CLEAR. VFR CONDITIONS THEN PREVAIL WITH HIGH CLOUDS
PASSING OVERHEAD. STRATUS IS THEN EXPECTED TO REDEVELOP LATE TONIGHT
AND SPREAD INLAND OVERNIGHT INTO TUESDAY MORNING. LIGHT WEST TO
NORTHWEST WINDS WILL INCREASE TO AROUND 4 TO 8 KT BY LATE THIS
MORNING AND PERSIST THROUGH THE REST OF THE DAY.
KSEA...VFR CIGS EARLY THIS MORNING WILL DETERIORATE TO LIFR ONCE
MARINE STRATUS ARRIVES AT THE TERMINAL, AROUND 12-13Z THIS MORNING.
MODELS ARE INDICATING A FAIRLY RAPID CLEAR OUT TIME, AROUND 17-19Z.
VFR CONDITIONS THEN PREVAIL THROUGH THE REMAINDER OF THE DAY, WITH
STRATUS EXPECTED TO RETURN AGAIN EARLY TUESDAY MORNING. LIGHT AND
VARIABLE WINDS WILL RETURN TO NW/N THIS MORNING AND INCREASE TO
AROUND 5-8 KT BY LATE MORNING AND REMAIN LIKE SO THROUGH
TONIGHT. 62
MARINE
HIGH PRESSURE WILL REMAIN OVER THE FAR OFFSHORE WATERS AND SLOWLY
BUILD THROUGH THE WEEK, WHICH WILL MAINTAIN NORTHWESTERLY WINDS OVER
THE COASTAL WATERS. WINDS LOOK TO INCREASE LATE TONIGHT INTO TUESDAY
OVER THE OUTERMOST WATERS, WHICH MAY DEVELOP STEEP SEAS AROUND 6-7
FT WITH A DOMINANT PERIOD OF 7 SECONDS. THE THREAT FOR STEEP SEAS
MAY CONTINUE THROUGH MID-WEEK. WESTERLY PUSHES DOWN THE STRAIT OF
JUAN DE FUCA LOOK TO CONTINUE INTO NEXT WEEK, BUT WILL WEAKEN EACH
DAY. GUSTS MAY OCCASIONALLY REACH 20-25 KT AT TIMES, IN PARTICULAR
THIS EVENING AND TUESDAY EVENING (UP TO 50% CHANCE), BUT NO
ADDITIONAL HEADLINES ARE PLANNED AT THIS TIME. 62
FIRE WEATHER
ONSHORE FLOW AND EXCELLENT OVERNIGHT HUMIDITY RECOVERIES WILL
HELP MITIGATE FIRE WEATHER CONDITIONS ACROSS WESTERN WASHINGTON
THROUGH THE FIRST HALF OF THE WEEK BEFORE A WARMING AND DRYING
TREND COMMENCES MID TO LATE WEEK.
WHILE SOME UNCERTAINTY REMAINS IN THE LONG TERM PATTERN, GUIDANCE
CONTINUES TO SUGGEST THAT THE NEXT STORM SYSTEM WILL ARRIVE BY
THE WEEKEND, INCREASING THE CHANCES FOR SHOWER AND THUNDERSTORM
ACTIVITY ACROSS THE AREA AND POTENTIALLY RESULTING IN THE RETURN
TO ELEVATED TO CRITICAL FIRE WEATHER CONDITIONS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 3 AM PDT EARLY THIS MORNING FOR
CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE
U.S. WATERS STRAIT OF JUAN DE FUCA.
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