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Napavine, Washington Weather Forecast Discussion

083
FXUS66 KSEW 201628
AFDSEW

Area Forecast Discussion National Weather Service Seattle WA 928 AM PDT Sat Sep 20 2025

.SYNOPSIS...Mostly dry and mild conditions continue today before a frontal system move through the area late tonight into Sunday morning, bringing widespread rain, breezy winds, and cooler temperatures. High pressure will return Monday for a return to sunny skies and warmer conditions through at least the first half of the week.

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.SHORT TERM /TODAY THROUGH MONDAY/...Skies remain mostly clear across much of western Washington, though marine stratus is developing along the coast and will push inland a little bit tonight. The Puget Sound area and the metro should remain under clear skies. Lows will be again be cool for this time of year, in the low 40s to low 50s. Stratus should quickly retreat, allowing the sun to warm us back up into upper 60s on the coast, with low to mid 70s for the interior.

Smoke from fires on the Olympic Peninsula will continue to degrade air quality through today, through this incoming system tonight into tomorrow should help to clear some of it out and improve air quality.

Clouds will start to increase in the evening as the frontal system approaches the area. Rain will first reach the coast late this evening, moving across the interior early Sunday morning. The heaviest rain will be before sunrise but showers may stick around into Sunday morning. Additionally, a convergence zone may keep some showers going over the metro area and towards the passes into Sunday afternoon. With the trough axis directly overhead by Sunday afternoon, there may be just enough instability for a lightning strike or two, but overall the probability is low (10-15%). Through Sunday afternoon, 0.5-1" will be possible across the mountains and the Pacific coast, with the interior receiving around 0.25-0.5" with this system. Definitely not a fire season- ender, but should bring a temporary reprieve for the active fires in the area. As the rain moves through overnight, low temperatures will be warmer, in the mid 50s, though Sunday`s high temperatures will remain quite cool, in the mid to upper 60s. Decreasing clouds Sunday night should allow lows to once again cool quite effectively, in the 40s to near 50 in the metro. Areas of fog will be expected Monday morning. Upper level ridging will quickly build over the area behind the trough Monday morning, allowing for a rapid return to mostly clear skies and more seasonable temperatures, with highs a few degrees on either side of 70 on Monday.

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.LONG TERM /TUESDAY THROUGH FRIDAY/... Upper level ridging looks to remain in place into Tuesday and Wednesday, allowing for a gradual warm-up, back into the mid to upper 70s. Lows remain in the 50s. The ridge looks to flatten around mid-week, which may allow systems to move through and reach the area by late week into next weekend and bring temperatures back close to/slightly below normal, however there is considerable uncertainty as to how quickly that occurs and whether or not incoming waves are able to sustain themselves to reach the Pacific Northwest. That being said, ensembles keep the area dry through Friday.

62

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.AVIATION...Southwest flow aloft will increase over Western Washington today as an upper level ridge shifts eastward a trough and associated frontal system approach the region. Most terminals are VFR this morning. Marine stratus and/or isolated shallow pockets of fog have brought LIFR conditions to the coast, Strait of Juan de Fuca, Kitsap Peninsula, and southwest interior. Improvement into VFR is expected for the interior terminals once the fog dissipates. Coastal terminals may improve to MVFR late this morning/early afternoon. Reduced visibility in smoke and haze will continue to affect areas downwind of the Bear Gulch Fire, especially south portions of Puget Sound eastward. High and mid level clouds will increase late this afternoon and tonight. MVFR ceilings in rain will develop along the coast this evening and will spread to the interior areas overnight.

KSEA...VFR at the terminal this morning and will prevail for the rest of today. High level smoke and haze will persist across the area through much of the day. High and mid level clouds ahead of an approaching front will increase this afternoon and evening, with ceilings lowering to MVFR in rain near or after 08Z tonight. Light surface winds this morning will increase out of the S/SW to 7 to 10 knots this afternoon and evening. Winds will become gusty for a period with and behind the front early Sunday morning.

27/29

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.MARINE...A weak surface ridge over the waters will give way to a weak trough and associated frontal system tonight into early Sunday. This will cause increased winds over area waters as the front pushes through and behind the front. High pressure will rebuild over the waters later Sunday into Monday. Another thermal trough expanding northward along the Oregon coast early next week will turn the flow more northerly or weakly offshore. Onshore flow will resume around midweek as another frontal system moving into British Columbia passes mostly north of the area.

27

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.SEW WATCHES/WARNINGS/ADVISORIES... WA...Air Quality Alert until midnight PDT tonight for Foothills and Valleys of Thurston and Lewis Counties-Foothills of the Western and Southern Olympic Peninsula-Lowlands of Lewis and Southern Thurston Counties-Middle Chehalis River Valley-Olympia and Southern Puget Sound-Olympics-Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory from 11 PM this evening to 1 PM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 1 AM to 9 AM PDT Sunday for Puget Sound and Hood Canal.

Small Craft Advisory from 2 PM this afternoon to 2 AM PDT Sunday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

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NWS SEW Office Area Forecast Discussion

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