482
FXUS66 KSEW 192144
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
244 PM PDT WED AUG 19 2026
SYNOPSIS
WEAK UPPER LEVEL RIDGE WITH LIGHT ONSHORE FLOW IN
THE LOWER LEVELS THROUGH THURSDAY. UPPER LEVEL LOW APPROACHING
FROM THE SOUTHWEST FRIDAY WILL MOVE INTO THE COASTAL WATERS
SATURDAY. SHOWER CHANCES INCREASING FRIDAY NIGHT INTO SATURDAY
WITH THUNDERSTORMS POSSIBLE. LOW MOVES BY TO THE NORTH SATURDAY
NIGHT. UPPER LEVEL RIDGE REBUILDING 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. THE STRATUS HAS CLEARED TO
THE WATERS OFFSHORE (INCLUDING THE COASTLINE) WITH TERMINALS
REPORTING VFR THIS AFTERNOON. ONLY A FEW HIGH CIRRUS LEVEL
CLOUDS REMAIN IN THE INTERIOR. 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 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
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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