373 FXUS66 KSEW 242138 AFDSEWArea Forecast Discussion National Weather Service Seattle WA 238 PM PDT Wed Sep 24 2025
.SYNOPSIS...Zonal flow will bring in more fall-like conditions across western Washington through the remainder of the week, with cooler temperatures and periods of cloudy skies. Periods of showers are possible Friday and Saturday before more widespread rain enters the region on Sunday and Monday. Unsettled and cooler conditions are favored to continue into next week.
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.SHORT TERM /TONIGHT THROUGH SATURDAY/...An upper level ridge over the western US will flatten throughout the remainder of the week as an upper level trough moves inland over British Columbia. Zonal flow will develop over western Washington by the afternoon today, generating onshore flow that will bring periods of cloudy skies and cooler temperatures. This shift to westerly winds will also help to push any remaining smoke to the east side of the Cascades by this evening. While temperatures today are on track to reach the mid 70s across much of the lowlands, stronger onshore flow Thursday will lower temperatures by several degrees, with most areas struggling to surpass the mid 60s.
As a deepening upper low in the Gulf of Alaska advects moisture towards the west coast of Canada, some shower activity may graze the northern portion of western Washington on Friday and Saturday, particularly along the northern Olympic Peninsula, over the San Juan Islands, and northern interior. Rainfall amounts will generally be light, with the highest rain likely over the northwestern Olympic Peninsula. Temperatures Friday and Saturday will
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...A frontal system is on track to cross the region on Sunday, bringing widespread rain and cooler temperatures to the region that will linger into next week. Between Sunday and Monday, ensembles are showing potential for a half inch or more of rainfall across the lowlands and up to 2 to 3 inches of liquid over the mountains. Another trough will follow close behind, maintaining chances for rain through the middle of next week. By the beginning of next week, temperatures will peak in the low to mid 60s across the lowlands.
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.AVIATION...Westerly flow aloft with a frontal system passing north of our area and an upper level ridge weakening. Light offshore flow in the lower levels will gradually turn onshore later in the evening. VFR at all terminals this afternoon with some smoke and haze aloft. Onshore flow will bring marine stratus through the coastal areas later this evening for IFR/LIFR conditions, along with stratus spreading through interior locations for a a mix of MVFR/IFR conditions by Thursday morning. Lowered conditions over the interior will burn off by 17-18z, rebounding back to VFR for most of the area.
KSEA...VFR conditions this evening with surface winds N/NE 6 to 8 knots, shifting more northwesterly overnight. MVFR/IFR stratus is likely at the terminal generally around 09-15z, with a 40% chance of MVFR conditions and a 20% chance of IFR conditions. Stratus looks to burn off by 18z, resuming VFR conditions throughout the remainder of the day. Surface winds shifting SW/S briefly in the morning before turning NW by the afternoon.
Mazurkiewicz
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.MARINE...Surface high pressure over the coastal waters this afternoon will lead to an increase in onshore flow later this evening. Increasing northwesterlies over the coastal waters will keep the small craft advisory in place for the outer coastal waters, and the southern inner coastal waters for a combination of winds and choppy seas. Onshore flow continues into Thursday where a westerly push down the Strait of Juan De Fuca may warrant a small craft advisory depending on the strength of the winds. A stronger front looks to reach the area Sunday night into Monday which could yield potential impacts for the area waters including headlines.
Combined seas 7 to 9 feet this afternoon decreasing briefly Thursday evening before building back up to 8 to 11 feet by Friday evening and hovering throughout first part of the weekend.
Mazurkiewicz
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.SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 11 AM PDT Thursday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 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