088 FXUS66 KSEW 130923 AFDSEWArea Forecast Discussion National Weather Service Seattle WA 223 AM PDT Sat Sep 13 2025
.SYNOPSIS...High pressure aloft will shift east of the region today and a weak front will move into the area late tonight and Sunday with showers and cooler temperatures. High pressure will rebuild across Western Washington early in the coming week for a brief return of warmer and drier conditions. The ridge will weaken by midweek as another weather system brushes the area and temperatures return to near or a little below seasonal normals.
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.SHORT TERM /TODAY THROUGH MONDAY/...An upper level ridge over Western Washington will shift eastward into the Northern Rockies today and weaken as a frontal system offshore approaches the area. Morning clouds will give way to some partial sunshine across interior areas today, but clouds will be summarily increasing by evening as the system approaches. Model QPF has backed off quite a bit in recent runs...due, in part, to the fact that the front will split as it moves ashore early Sunday. This leaves some question as to how much precipitation will actually make it east of Puget Sound. However, there will be some post-frontal convergence zone activity by midday Sunday and that ought to generate upwards of a quarter to locally a half inch of precip for portions of the Cascades in King and Snohomish Counties. As one might expect, temperatures will take a tumble on Sunday with most lowland locations staying in the 60s. Upper ridging begins to rebuild into the area Sunday night into Monday while thermally induced low pressure at the surface expands northward along the Oregon coast. This will lead to drier and somewhat warmer conditions on Monday.
.LONG TERM /TUESDAY THROUGH FRIDAY/...The previously mentioned thermal trough reaches the Washington coast on Tuesday turning the low level flow offshore. This will result in a pretty sharp, albeit brief, warmup across Western Washington with both coastal areas and interior locations warming into the 70s to lower 80s. The flow is expected to quickly turn onshore Tuesday night into Wednesday as another weather system approaches the area. And this is where the forecast details turn a little murky. While there`s fairly good agreement in the models that cooler temperatures will return, the ensembles are still split with respect to QPF potential. Nonetheless, this does appear to signal something of seasonal turning point with a more active pattern taking shape over the northeast Pacific. The balance could soon begin to tip toward autumn. 27
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.AVIATION...Light westerly flow aloft will transition southerly late today into early Sunday as a frontal system approaches Western Washington. Onshore flow continues at the surface. LIFR/IFR stratus is slowly spreading inland early this morning. In addition, a lingering low-end VFR or MVFR deck exists across portions of Puget Sound and into the Cascades. Cigs will lower for most interior sites into Saturday morning, along with areas of vsby reduction as well due to low stratus or patchy fog. LIFR/IFR along the coast. Slow improvement in cigs to VFR for Saturday afternoon for interior locations with increasing mid and high clouds later today. Showers are expected to reach the coast late tonight into Sunday morning. Light winds this morning will increase from the S/SW this afternoon.
KSEA...VFR conditions early this morning with a lingering MVFR to low-end VFR deck into the Cascades, and stratus spreading into the Southwest Interior. There remains some uncertainty into how extensive low stratus (IFR or lower) is across Puget Sound this morning. However, cigs are expected to lower into MVFR/IFR generally after 12z to 13z through midday. Cigs may also lower at times to LIFR mainly between 13 to 17z, but confidence remains low. Otherwise, cigs are expected to lift by Saturday afternoon, with VFR mid and high clouds later in the day. Light winds this morning will become S/SW this afternoon. JD
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.MARINE...A weather system will approach the Coastal Waters today and move inland on Sunday, resulting in increasing winds for the waters. Southerly winds will peak for the Coastal Waters this afternoon through Saturday evening before transitioning to more northwesterly on Sunday. Brief Small Craft Advisory wind gusts, between 20 to 25 kts, are possible for the central and northern outer Coastal Waters during this period, and have issued a SCA for these areas this afternoon.
Onshore flow will increase on Sunday, resulting in a westerly push through the Strait of Juan de Fuca, where SCA winds will be possible. After the weather system moves through, a brief period of offshore flow is expected on Tuesday before another potential front midweek.
A Dense Fog Advisory has also been issued through this morning for the inner Coastal Waters and Grays Harbor Bar with visibilities less than 1 NM for these areas.
Seas will remain 6 to 8 feet through the weekend, with a period dropping to near 8 seconds briefly tonight. Seas will then subside to 4 to 6 feet Monday before building midweek. JD
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.SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Dense Fog Advisory until 11 AM PDT this morning for Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-Grays Harbor Bar. Small Craft Advisory from 11 AM this morning to 8 PM PDT this evening 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.
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NWS SEW Office Area Forecast Discussion