Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS66 KSEW 040346 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 846 PM PDT Tue Oct 3 2023 .UPDATE...
-- Changed Discussion --
No changes to the overall forecast. Please see the aviation and marine sections below for updates to those forecasts.
-- End Changed Discussion --
&& .PREV DISCUSSION...
-- Changed Discussion --
/issued 219 PM PDT Tue Oct 3 2023/
-- End Changed Discussion --
&& .SYNOPSIS...
-- Changed Discussion --
An upper ridge located offshore will build over Western Washington into Wednesday. Light low level flow will keep moisture near the surface through Wednesday, however, resulting in times of drizzle or light showers. Increasing northerly and offshore flow into Thursday. A warmer, drier pattern Thursday into the weekend. A more active pattern early next week. .SHORT TERM /TONIGHT THROUGH FRIDAY/...Mostly cloudy conditions this afternoon for most of Western Washington with generally clear skies across the northern Olympic Peninsula and towards the San Juan Islands. Some clearing into this evening with increasing clouds tonight into Wednesday morning as a trough moves across southern Canada, bringing some slight enhancement to precipitation potential Wednesday morning. Generally light rain and drizzle will exist during this period. Conditions will become drier later Wednesday into Wednesday night as upper ridging builds more into the Pacific Northwest. The upper ridge will bring more northerly flow on Thursday with low level offshore flow developing on Friday. Given the abundant moisture at the surface and clear skies, fog development will be likely Thursday morning, as well as Friday morning. However, clearing is expected each afternoon with increasing winds. Temperatures will also warm Thursday into the mid 60s to low 70s, and further Friday into the 70s for most areas, and even a few 80s are possible in the Cascade valleys. .LONG TERM /SATURDAY THROUGH TUESDAY/...The upper ridge situated across the Pacific Northwest late week will slowly progress eastward over the weekend. Saturday will likely be the warmest day for the interior, with widespread 70s. There is some spread in guidance, however, with NBM suggesting a 20% chance of KSEA reaching 80 degrees Saturday afternoon. Onshore flow will then begin to increase on Sunday as the ridge shifts east, and troughing developing across the NE Pacific. This will allow for increasing clouds, as well as some cooling. In addition, ensemble guidance suggests the potential for increasing precipitation beginning Sunday afternoon for the Olympic Peninsula. A more active period of weather is likely beginning late Sunday into Monday with a frontal system tapping into sub-tropical moisture for increasing rain and perhaps breezy winds. Troughing will likely dominate the pattern into Tuesday for cooler weather and potential showers. JD .AVIATION...Northwest flow aloft will continue as broad ridging offshore starts to nudge closer to W WA. A few scattered clouds remain over the Puget Sound lowlands, while marine stratus is beginning to make its way onshore. Low MVFR ceilings make their way into the Puget Sound lowlands around 06z-09z and continue into Wednesday morning. Conditions will likely deteriorate to IFR as we head into the morning, with a 40% chance of IFR ceilings through the interior heading into 15z. With light low level flow, and a more stable airmass filtering into the region, patchy fog will be possible tomorrow morning through interior terminals, and can locally deteriorate conditions to even LIFR, especially around 12z-16z. KSEA...VFR conditions with a few mid-level clouds present. West/southwest winds have gone to calm conditions. Low MVFR clouds return tonight around 10z-12z, with at least a 25 to 35 percent chance of LIFR ceilings heading into 13z-16z. Winds will remain lightly out of the south, then will switch to light northerly winds after 19Z. Mazurkiewicz/LH
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Surface ridging will continue to amplify offshore, with northwesterlies over the coastal waters. Low clouds and significant moisture near the surface will likely generate fog, which may become dense into tomorrow morning. Ensembles indicate around a 40% chance of visibilities less than 1 NM for the coastal waters north of James Island and into the West Entrance of the Strait of Juan de Fuca. Patchy dense fog will remain possible for the aforementioned areas through tomorrow night. A thermally induced trough will start to develop near the coastline on Thursday,shifting inland on Friday, with offshore flow through the interior waters. Small Craft Advisory easterlies look to be possible Thursday night into Friday for the Central and Eastern Strait of Juan De Fuca. Coastal seas around 6 to 8 feet this afternoon will gradually subside to around 4 to 6 feet through midweek. Mazurkiewicz/LH
-- End Changed Discussion --
&& .HYDROLOGY...No river flooding is expected through the next seven days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.