textproduct: Seattle/Tacoma

UPDATE

Main forecast issue this evening and tonight will be the presence of low stratus and fog over portions of western Washington, Already starting to see this development over much of the western half of the CWA. Stratus over the south Sound may inhibit fog development this evening, but hard to see that lasting into the overnight hours. Inherited forecast remains on track.

SYNOPSIS

Strong high pressure will linger throughout the rest of the week and into the weekend. Drier conditions and light flow will lead to periods of fog, dense at times, each night and morning across the lowlands.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

Stratus and pockets of fog have already begun developing this afternoon, with more widespread fog expected overnight. It has also been a very mild afternoon, with temperatures at the time of this writing largely being in the mid to upper 50s across western Washington.

Each night and into the morning hours through the weekend will bring about new rounds of fog. The afternoon high temperatures going forward will need to be watched as the impact of fog could act to cool them down by a few degrees. This could also impact the overnight lows, making them a little bit warmer than what is presently forecast. Be mindful of limited visibilities at night and in the morning during the commute times over the next several days.

A weak system will brush the area to the north on Wednesday, but will have very little impact on the expected weather. The ridge will flatten only slightly. Offshore flow kicks up a little bit on Thursday and into Thursday night, with the potential for easterly wind gusts of 15-20 mph. Thursday would be the day, given the offshore winds, with the best potential for more clearing, but fog and stratus will still likely be stubborn in the south Sound and toward the coast.

LONG TERM /FRIDAY THROUGH TUESDAY/

Long term forecast indications point to the high pressure hanging on in through the weekend. Skies may clear up to offer more sunshine Friday into the weekend, with mild afternoon highs in the 50s. Fog coverage is likely to expand early next week as the high pressure shifts more inland.

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AVIATION

W/SW flow aloft will persist through the TAF period as an upper level ridge remains situated over western Washington. Conditions at the area terminals generally range between MVFR in low clouds to IFR/LIFR in fog this evening. Expect IFR to LIFR cigs and visibilities to become more widespread tonight with ample moisture in the low levels and light flow promoting fog development. Areas of dense fog will then be likely tonight into Wednesday, with fog expected to be slow to lift on Wednesday. Areas across the central and south Sound may not even break out. Surface winds will be light at 6 kts or less into Wednesday afternoon.

KSEA...MVFR cigs at the terminal this evening There is high confidence in fog development tonight into Wednesday morning, with LIFR conditions developing after 06z. Expect fog to be slow to lift on Wednesday, with improvement to IFR/MVFR only expected by the afternoon hours. Winds will remain light at 3-6 kt out of the north tonight and look to become more variable during the overnight hours.

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MARINE

Surface high pressure will persist across area waters tonight into early Wednesday, before a weak frontal boundary moves into the region and dissipates over the outer coastal waters on Wednesday afternoon. A strong surface high over the northeastern Pacific will then move into the interior of British Columbia on Thursday, while a thermal trough builds along the coast. This will bring a period of offshore flow towards the end of the week, which may get gusty at times near the gaps in coastal terrain.

Seas have subsided towards 7-9 ft this afternoon, however another decaying swell train moving into the region on Wednesday will push seas back to 10-12 ft. Seas will then gradually subside again on Thursday and will persist between 3-6 ft Friday and through the weekend.

Areas of dense fog will likely develop across the area waters over the next few nights and could reduce visibilities down to 1 nautical mile or less at times.

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HYDROLOGY

The Skokomish River has crested and continues recede this afternoon. The river remains in Minor flood stage and will likely fall out of flood stage later tonight. With precipitation having ended across western Washington, flooding is no longer expected on the rivers in Whatcom and Skagit counties, so have cancelled the flood watches for those areas. Drier weather will persist through much of the next week, with no additional river flooding expected.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 10 AM to 7 PM PST Wednesday for Grays Harbor Bar.

Small Craft Advisory from 4 AM Wednesday to 1 AM PST Thursday 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.