textproduct: Seattle/Tacoma

UPDATE

Areas of dense fog continue to move through parts of western Washington this morning. Based on satellite and webcams, no changes were made to the advisory areas yet this morning. Ceilings look to remain around 100-300 ft, so the areas closest to sea level may no longer see dense fog. Guidance continues to indicate fog starting to lift around 10-11 AM, with more clearing shortly thereafter with high clouds continuing to stream overhead. See below for updates the the aviation discussion. 62

SYNOPSIS

Near-zonal flow aloft and onshore flow at the surface will maintain seasonable conditions across western Washington through much of the week, with morning clouds and afternoon sun breaks. Chances for rain increase towards the end of the week alongside cooler temperatures as troughing develops over the Pacific Northwest.

SHORT TERM /TODAY THROUGH WEDNESDAY/

An upper level ridge over the Great Basin has weakened and flattened, allowing for zonal flow to develop aloft over the Pacific Northwest with a return to onshore flow at the surface. The pattern is set to remain steady throughout the short-term, resulting in little change day to day through Wednesday. Daily marine pushes will result in expanding stratus across the lowlands each morning, with potential for patchy fog to develop in fairly stagnant overnight conditions. The fog and stratus will erode for most lowland areas by the afternoon each day, although areas along the coast may stay socked in with little sunshine. The cooler marine air will allow for seasonable fall temperatures, with highs generally in the 60s to lower 70s, and lows in the mid 40s to lower 50s. The upper level ridge over the southwestern US will rebound slightly on Wednesday, resulting in little more than temperatures a degree or two warmer across the region.

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

The upper level high pressure ridge over the southwestern US will continue to nudge into the Pacific Northwest slightly on Thursday, resulting in continued warming with high temperatures in the mid 60s to lower 70s. However, conditions on Thursday will feel similar to past days with another potential round of low stratus in the morning and sunny skies in the afternoon.

Forecast models remain in good agreement of troughing developing over the region on Friday into the weekend, but the details still remain fairly uncertain. Models have continued to back off on incoming rainfall on Friday with a frontal system splitting as it moves into western Washington, though ensembles hint at a potential Puget Sound convergence zone developing into Saturday. A cutoff low is also expected to develop overhead by Saturday, bringing cooler temperatures and chances for light showers lingering into Sunday. The exact details remain uncertain at this time, but next weekend looks to be cooler and unsettled with highs peaking in the mid 50s to lower 60s.

15

AVIATION

Onshore flow this morning has led to widespread areas of fog this morning, primarily from central Puget Sound southward, and north of Everett. The areas of fog/mist will likely begin lifting as early as 18Z, and then fully scatter out for all except the coast/Strait of Juan de Fuca by 20-22Z. The two coasts likely retain MVFR ceilings into the afternoon/evening. Given the continuing/stagnant onshore pattern with high pressure offshore, another round of fog/mist is likely to develop Tuesday morning. Light and variable winds this morning will increase out of the north around 4-6 kt this afternoon, becoming calm/light and variable again tonight.

KSEA...Fog/LIFR conditions will continue at the terminal through 18Z, with conditions improving from 18-21Z this afternoon to VFR. Another round of lower ceilings/fog is likely Tuesday morning, although uncertainty exists as to how far fog will make it up to the terminal. Calm/light and variable winds will be present this morning/Tuesday morning, with winds picking up out of the northeast at around 4-6 kt both Monday/Tuesday afternoon.

HPR

MARINE

Onshore flow has returned into today as low pressure shifts inland and surface high pressure builds offshore. Areas of fog continue across portions of Puget Sound, the Strait of Juan de Fuca, and the Northern Inland Waters where dense fog advisories continue through 11 AM this morning. Fog will be likely over portions of the waters next few mornings. Westerly pushes are favored throughout the upcoming week of varying strength. A more organized system appears favorable towards Friday with a better chance of widespread headlines.

Seas through Wednesday hold at 4-6 ft, and increase to 6-10 ft late this week with the late week systems passing through.

41/HPR

SEW WATCHES/WARNINGS/ADVISORIES

WA...Dense Fog Advisory until noon PDT today for City of Seattle- Downtown Everett / Marysville Area-Eastern Strait of Juan de Fuca-Eastside-Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Grays Harbor County Coast-Island County-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties-Middle Chehalis River Valley-Olympia and Southern Puget Sound-San Juan County- Shoreline / Lynnwood / South Everett Area-Western Strait of Juan de Fuca-Willapa and Black Hills.

PZ...Dense Fog Advisory until 11 AM PDT this morning for Admiralty Inlet-Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.