774
FXUS66 KSEW 200322
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
822 PM PDT WED AUG 19 2026
SYNOPSIS
WEAK UPPER LEVEL RIDGE WITH LIGHT ONSHORE SURFACE FLOW
THROUGH THURSDAY. AN UPPER LEVEL LOW APPROACHING FROM THE SOUTHWEST
ON FRIDAY WILL MOVE INTO THE COASTAL WATERS SATURDAY. SHOWER CHANCES
INCREASING FRIDAY NIGHT INTO SATURDAY WITH THUNDERSTORMS POSSIBLE.
LOW EXITS TO THE NORTH SATURDAY NIGHT. UPPER LEVEL RIDGING SUNDAY
AND MONDAY WILL MOVE EAST TUESDAY AS AN UPPER LEVEL TROUGH DEVELOPS
OFF THE COAST.
SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/
DRY AND MILD
WEATHER IS EXPECTED ACROSS WESTERN WA THROUGH FRIDAY WITH HIGH
PRESSURE OVER THE AREA. THE LOW LEVEL FLOW REMAINS ONSHORE FOR
MORNING CLOUDS AND AFTERNOON SUNBREAKS. TEMPERATURES WILL TRACK
CLOSE TO AVERAGE. AN UPPER LEVEL LOW WILL SPIN OFFSHORE FRIDAY
NIGHT THEN START TO SHIFT INLAND. THE AIR MASS WILL BE SLIGHTLY
UNSTABLE UNDER MOIST, DIFFLUENT FLOW. THIS MAY RESULT IN HIGH-
BASED, LIGHT SHOWERS OVER THE SOUTHERN PORTION OF THE CWA
FRIDAY NIGHT. THERE'S A LOW-END (10-15%) CHANCE OF
THUNDERSTORMS IN THE SOUTHERN CASCADES. 33
LONG TERM /SATURDAY THROUGH WEDNESDAY/
AN UPPER LEVEL TROUGH
WILL PUSH INTO WESTERN WA ON SATURDAY BRINGING SHOWERS, A CHANCE
OF THUNDERSTORMS AND COOLER CONDITIONS. RAINFALL AMOUNTS ARE
GENERALLY UNDER 0.10" WITH THE HIGHEST CHANCES OF WETTING RAINS
OVER THE NORTHERN CASCADES NEAR THE CANADIAN BORDER.
TEMPERATURES WILL BE COOLER AND IN THE 60S TO LOWER 70S. THE
LOW WILL SHIFT NE INTO B.C. ON SUNDAY WITH A FEW LINGERING
SHOWERS OVER WESTERN WA. MOVING FORWARD, WE'RE BACK TO MAINLY
DRY AND MILD CONDITIONS EARLY NEXT WEEK AS WEAK HIGH PRESSURE
RETURNS AND LOW PRESSURE REMAINS OFFSHORE. 33
AVIATION
SOUTHWEST FLOW ALOFT WILL CONTINUE WITH WEAK LOW
LEVEL ONSHORE FLOW THROUGH THURSDAY. ONLY A FEW HIGH CIRRUS LEVEL
CLOUDS REMAIN IN THE INTERIOR WITH VFR CONDITIONS. WINDS ARE
BEGINNING TO SHIFT TO THE NORTHWEST, BUT MOST LOCATIONS WILL SEE
THEM ONLY RANGE 4-6 KT THROUGH THE EVENING (WITH A FEW POTENTIALLY
REACHING 8 KT). WINDS BECOME CALM OR LIGHT AND VARIABLE FOR MOST
LOCATIONS TONIGHT. ANOTHER MARINE PUSH IS LIKELY FOR THURSDAY
MORNING FOR THE SAME AREAS AS THE PREVIOUS NIGHT. THE LIGHT WINDS
MAY RESULT IN SOME MIST AND FOG MIXING IN WITH THE LOW STRATUS, BUT
IN GENERAL IFR/LIFR CHANCES REMAIN HIGHEST FROM THE KITSAP PENINSULA
WESTWARD. FORMATION TIME WILL BE FROM ROUGHLY 06Z ALONG THE COAST,
TO 10-12Z IN THE INTERIOR, WITH CLEARING TIME RANGING FROM 16-18Z IN
THE INTERIOR, TO 20-22Z ALONG THE COAST. WINDS THURSDAY WILL PICK UP
OUT OF THE NORTHWEST DURING THE DAY AT 4- 6 KT.
KSEA...VFR THROUGH ROUGHLY 12Z, THEN STRATUS LIKELY REACHING THE
TERMINAL AT AROUND 12Z AND LASTING THROUGH 16-18Z BEFORE CLEARING.
IFR/LIFR PROBABILITIES CONTINUE TO REMAIN ELEVATED ENOUGH (ALONG
WITH FORECAST/PATTERN CONSISTENCY) FOR THE FORECAST OF LOW CEILINGS
IN THE MORNING, ALTHOUGH THE LIKELIHOOD FOR FOG/MIST REMAINS LESS
THAN 5%. NORTHWEST WINDS SHIFTING TO THE NORTH 4-6 KT THROUGH THE
EVENING, THEN MOST LIKELY BECOMING CALM OR LIGHT/VARIABLE OVERNIGHT,
BEFORE PICKING BACK UP FROM THE NORTHWEST LATER THURSDAY.
HPR/MAZURKIEWICZ
MARINE
HIGH PRESSURE OVER THE WATERS WILL WEAKEN GOING INTO
FRIDAY. A WEAK SURFACE LOW AND TROUGH WILL MOVE OVER THE WATERS
SATURDAY WITH A WEAK FRONTAL SYSTEM. THERE IS A SLIGHT CHANCE OF
SHOWERS AND ISOLATED THUNDERSTORMS FOR THE INTERIOR WATERS
GOING INTO SATURDAY AFTERNOON. A FEW WEAKER PUSHES THROUGH THE
STRAIT OF JUAN DE FUCA APPEAR LIKELY GOING INTO THE WEEKEND AS A
RESULT OF THIS FRONT, ALTHOUGH CONFIDENCE REMAINS LOW IN ANY OF
THE WINDS MEETING ADVISORY THRESHOLDS FOR SMALL CRAFT.
ADDITIONALLY, SOME PORTIONS OF THE PUGET SOUND WATERS MAY ALSO
GET A TOUCH BREEZY SATURDAY AFTERNOON AS THE FRONT PUSHES
THROUGH. OTHERWISE, BENIGN CONDITIONS ARE EXPECTED GOING INTO
NEXT WEEK.
SEAS WILL HOLD AT ROUGHLY 3 TO 6 FT DURING THE FORECAST PERIOD.
HPR
FIRE WEATHER
MILD CONDITIONS AND ONSHORE FLOW PROMOTING HIGH
OVERNIGHT RELATIVE HUMIDITY RECOVERIES WILL KEEP FIRE WEATHER
CONCERNS AT A MINIMUM THROUGH THURSDAY.
AN UPPER LEVEL TROUGH WILL MOVE INTO THE PACIFIC NORTHWEST LATER ON
FRIDAY AND INTO THE WEEKEND, BRINGING ELEVATED FIRE WEATHER
CONCERNS. THUNDERSTORMS ARE FORECAST TO DEVELOP OVER THE
SOUTHWESTERN CASCADES LATE FRIDAY AND EXPAND NORTHWARD THROUGHOUT
THE DAY SATURDAY. THE HIGHEST CHANCES FOR CONVECTION ARE OVER THE
OLYMPICS AND CASCADES (25-35% CHANCE), THOUGH THE LOWLANDS COULD
ALSO SEE SOME THUNDERSTORM ACTIVITY ON SATURDAY. RAINFALL AMOUNTS
HAVE INCREASED FOR THIS SYSTEM, AND LOCALIZED WETTING RAINS ARE
POSSIBLE WITH ANY STORMS THAT DEVELOP ALONGSIDE GUSTY AND ERRATIC
OUTFLOW WINDS AND ABUNDANT LIGHTNING. HOWEVER, THE AIR MASS MOVING
INTO WESTERN WASHINGTON IS MUCH COOLER AND MORE MOIST, SO ANY
LIGHTNING STRIKES MAY NOT HAVE LONG TO SMOLDER WITH MINIMUM RELATIVE
HUMIDITY VALUES BOTTOMING OUT IN THE 60-70% RANGE SATURDAY.
CONDITIONS WILL CALM ON SUNDAY AS THE STORM SYSTEM MOVES OUT OF THE
REGION AND ONSHORE FLOW RESUMES, BRINGING BACK CONTINUED HIGH
RELATIVE HUMIDITY RECOVERIES. THIS WILL ALSO BE ACCOMPANIED BY
MORNING LOW STRATUS AND AFTERNOON SUN, NEAR NORMAL TEMPERATURES, AND
GENERALLY CALM WINDS INTO THE MIDDLE OF NEXT WEEK.
15
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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