826
FXUS66 KSEW 182213
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
313 PM PDT TUE AUG 18 2026
SYNOPSIS
WEAK UPPER LEVEL RIDGE OVER THE AREA THROUGH
THURSDAY WITH VARYING DEGREES OF LOW LEVEL ONSHORE FLOW. UPPER
LEVEL LOW WELL OFFSHORE SLOWLY MOVING NORTHEAST AND OFF THE
COAST FRIDAY. WEAK SYSTEM SPINNING OUT OF THE LOW COULD PRODUCE
SOME SHOWERS OVER THE AREA FRIDAY. LOW MOVING THROUGH SATURDAY
KEEPING A CHANCE OF SHOWERS IN THE FORECAST FOR SOME LOCATIONS.
WEAK UPPER LEVEL RIDGE WITH LOW LEVEL ONSHORE FLOW RETURNS
LATER SUNDAY INTO THE FIRST PART OF NEXT WEEK.
SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/
WEAK UPPER LEVEL
RIDGING WILL LEAD TO DRY AND MILD WEATHER ACROSS WESTERN WA
THROUGH THURSDAY. THE LOW LEVEL FLOW REMAINS ONSHORE.
TEMPERATURES WILL TRACK CLOSE TO AVERAGE WITH A SLIGHT UPTICK ON
THURSDAY. 33
LONG TERM /FRIDAY THROUGH TUESDAY/
AN UPPER LEVEL LOW WILL
SPIN OFFSHORE ON FRIDAY, THEN SHIFT INLAND ON SATURDAY FOR
INCREASING SHOWERS AND COOLER WEATHER. THE AIR MASS WILL BE
SLIGHTLY UNSTABLE FOR A CHANCE OF THUNDERSTORMS IN THE MOUNTAINS
SATURDAY AFTERNOON (EASTERN OLYMPICS AND NORTHERN CASCADES).
HIGHEST CHANCES FOR WETTING RAINS WILL BE IN THE NORTHERN
CASCADES NEAR THE CANADIAN BORDER. WITH THE TROUGH OVERHEAD,
EXPECT COOLER CONDITIONS ON SATURDAY WITH HIGHS IN THE 60S TO
LOWER 70S. WE'LL SEE LINGERING SHOWERS ON SUNDAY AS THE TROUGH
EXITS NE. OTHERWISE, WERE BACK TO DRY AND MILD WEATHER MOVING
INTO NEXT WEEK AS WEAK HIGH PRESSURE RETURNS. 33
AVIATION
VFR THIS AFTERNOON FOR INTERIOR TERMINALS AND MVFR
ALONG THE COAST. CONDITIONS WILL DETERIORATE TONIGHT INTO
WEDNESDAY MORNING AS ANOTHER ROUND OF MARINE STRATUS PUSHES
INLAND. GUIDANCE CONTINUES TO STRUGGLE WITH HOW LOW THE CEILINGS
WILL GET, BUT BASED OF PERSISTENCE, IT IS POSSIBLE THAT THAT
CEILINGS WILL TREND TOWARD IFR/LIFR AGAIN. HIGH-RES GUIDANCE
SHOWS THERE IS A 50-70% CHANCE FOR IFR/LIFR FOR THE INTERIOR
TERMINALS. ADDITIONALLY, REDUCTIONS IN VISIBILITY ARE POSSIBLE
WITH THE STRATUS. UNCERTAINTY REMAINS AS TO HOW LOW VISIBILITY
WILL BE, BUT COULD SEE VISIBILITIES LOWER THAN 3SM. THE STRATUS
WILL RETREAT TOWARDS THE COAST/SCATTER OUT IN THE AFTERNOON
AFTER 19Z. VFR FOR INTERIOR TERMINALS IN THE AFTERNOON/EVENING
AND MINIMAL IMPROVEMENT ALONG THE COAST TO MVFR.
GENERALLY SW WINDS THIS AFTERNOON. WINDS MAY TRANSITION WNW AT
BFI/SEA THIS EVENING BETWEEN 00-06Z. PROBABILITIES ARE SLIGHTLY
HIGHER FOR BFI TO SEE WNW, WITH PROBABILITIES TRENDING TOWARDS 70-
80%. OTHERWISE, CALM TO LIGHT SW WINDS OVERNIGHT.
KSEA...VFR WILL PREVAIL TODAY. WHILE GUIDANCE CONTINUES TO STRUGGLE
WITH HOW LOW THE CEILINGS WILL BE WEDNESDAY MORNING, SOME HIGH-RES
GUIDANCE HAS A 50% CHANCE FOR LIFR AND 65% FOR IFR AFTER 12Z. BASED
OFF PERSISTENCE, WILL TREND THE TAF TOWARDS IFR/LIFR FOR TOMORROW
MORNING. CEILINGS WILL SLOWLY IMPROVE THROUGHOUT THE LATE MORNING
AND SCATTER OUT BY THE AFTERNOON, WITH VFR FOR WEDNESDAY AFTERNOON.
GENERALLY SW WINDS 3-6 KT TODAY. WINDS WILL SHIFT MORE TOWARDS THE
WSW THIS EVENING AND MAY SWITCH WNW (60% CHANCE) BETWEEN 01-06Z, BUT
SHOULD REMAIN LIGHT AROUND 5 KT. LIGHT WSW WINDS OVERNIGHT.
29
MARINE
BROAD HIGH PRESSURE OVER THE NORTHEAST PACIFIC WILL
CONTINUE BUILDING INTO AREA WATERS THROUGH TOMORROW. A WEAK
SYSTEM WILL APPROACH THE WATERS TODAY, BUT IS NOT EXPECTED TO
SIGNIFICANT IMPACTS. INCREASED NW SURFACE WINDS THROUGH
WEDNESDAY AND ARE EXPECTED TO REMAIN BELOW SCA THRESHOLDS. HIGH
PRESSURE WILL THEN WEAKEN THROUGH LATE IN THE WEEK AS A STRONGER
WEATHER SYSTEM APPROACHES AND MOVES OVER THE WATERS ON FRIDAY.
THIS MAY RESULT IN SCA WINDS THROUGH THE STRAIT OF JUAN DE FUCA
FRIDAY EVENING, WITH LATEST PROBABILITIES AROUND 60-70% THROUGH
THE CENTRAL PORTION. OVER THE WEEKEND, HIGH PRESSURE WILL
REBUILD AND STRENGTHEN OVER AREA WATERS.
SEAS WILL REMAIN BELOW 10 FEET THROUGHOUT THE WEEK. HOWEVER, SEAS
MAY BECOME STEEP AT TIMES FOR THE OUTER COASTAL WATERS TODAY THROUGH
THURSDAY AT 5-7 FT WITH A DOMINANT PERIOD OF 7 SECONDS.
29
FIRE WEATHER
CONTINUED ONSHORE FLOW THROUGH THURSDAY WILL
MAINTAIN MILD TEMPERATURES PAIRED WITH EXCELLENT OVERNIGHT
RELATIVE HUMIDITY RECOVERIES, LIMITING FIRE WEATHER CONCERNS
ACROSS WESTERN WASHINGTON.
A STORM SYSTEM APPROACHING THE REGION WILL CAUSE ELEVATED FIRE
WEATHER CONCERNS ON FRIDAY, BRINGING INCREASED POTENTIAL FOR
THUNDERSTORMS OVER THE OLYMPICS AND CASCADES. WHILE THERE IS STILL A
BIT OF UNCERTAINTY WITH THE TIMING AND INTENSITY OF THIS WEATHER
SYSTEM, ANY THUNDERSTORMS THAT DEVELOP MAY BE CAPABLE OF PRODUCING
LOCALLY WETTING RAINS ALONGSIDE GUSTY AND ERRATIC OUTFLOW WINDS AND
ABUNDANT LIGHTNING. WHILE CONVECTION MAY CONTINUE OVERNIGHT, A
FRONTAL SYSTEM WILL CROSS THE REGION SOMETIME BETWEEN FRIDAY EVENING
AND SATURDAY, BRINGING IN A MUCH COOLER AND MORE MOIST AIR MASS.
WIDESPREAD GUSTY WINDS ARE NOT EXPECTED BEHIND THE FRONTAL PASSAGE,
THOUGH MODELS CONTINUE TO SHOW POTENTIAL FOR CONVECTION AND A
POTENTIAL PUGET SOUND CONVERGENCE ZONE ON SATURDAY.
FIRE WEATHER CONCERNS DECREASE INTO SUNDAY, AS A DRIER AND CALMER
PATTERN SETS UP OVER WESTERN WASHINGTON. THIS WILL LIKELY BRING A
RETURN TO ONSHORE FLOW WITH MORNING LOW STRATUS AND AFTERNOON SUN,
NEAR NORMAL TEMPERATURES, AND GENERALLY CALM WINDS.
15
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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