textproduct: Seattle/Tacoma

UPDATE

Satellite imagery shows stratus and fog further inland this evening versus Sunday night. Surface gradients remaining light so like the previous early morning hours the stratus and fog will form in place over the Puget Sound area. The marine layer is shallow with locations around about 700 feet actually above the layer and in the sunshine in the morning. Same story as today with the stratus amd fog dissipating around noon give or take an hour. Light flow again Wednesday morning for another round of morning low clouds and fog. Made a small change to the forecast to add more clouds and fog Tuesday and Wednesday morning. Remainder of the forecast is unchanged. Previous discussion follows with updated aviation and marine sections. Felton

SYNOPSIS

Zonal flow to weak ridging aloft and light flow at the surface will maintain seasonably warm conditions across western Washington through much of the week, with morning clouds and fog followed by afternoon sun breaks. Chances for rain increase towards Friday into the weekend alongside cooler temperatures as troughing develops over the Pacific Northwest.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

The overall weather pattern look to remain fairly similar through Thursday as mostly zonal flow trends towards slightly higher 500 mb heights by mid-week as the ridge over the southwestern U.S. expands. What that translates to for the Pacific Northwest is a routine pattern of morning clouds and fog, giving way to sunnier afternoons with high clouds overhead. Chances for fog will be greatest today as light winds will this afternoon and tonight, and continued moisture will help promote the redevelopment of the marine layer and areas of dense fog. Slightly stronger winds Tuesday and Wednesday may help to trend things towards stratus and less fog by mid-week, but areas of patchy fog will still remain possible in the sheltered valleys.

Temperatures will remain seasonably warm across the area with highs in the mid 60s to low 70s. Lows remain in the upper 40s to mid 50s.

LONG TERM /THURSDAY THROUGH MONDAY/

Upper level ridging looks to gain its greatest influence across Washington on Thursday, therefore also forecast to be the warmest day of the week with highs in the upper 60s to mid 70s.

Most models agree on the development of an upper level trough digging into the Pacific Northwest Friday into the weekend. There will be some slight chances for showers across portions of the area but widespread rain does not look very likely with this system. There remains some uncertainty in the exact timing but Friday into Saturday have the best chances at this time. But an increase in clouds and an increase in winds is to be expected. Cooler temperatures also looks to be in store with highs dipping into the upper 50s to low 60s this weekend, with lows in the upper 30s to mid 40s.

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AVIATION

A flat upper ridge will remain over the region into Tuesday with westerly flow aloft continuing. The low level flow is light onshore and will shift more northerly on Tuesday in response to thermally induced low pressure expanding northward across Oregon. Light surface winds and the lengthening night will be favorable for widespread low cloud and/or fog formation overnight with much of the lowlands seeing LIFR ceilings and reduced surface visibility below 3SM toward 12Z Tuesday. Low clouds will gradually lift and scatter most areas 19Z-21Z.

KSEA...Expecting conditions to deteriorate near or after 09Z with LIFR ceilings and visibility dropping below 2SM at times by 12Z. These conditions will likely hang around through 18Z before a gradual improvement with VFR returning around 20Z. Surface winds light and variable overnight will become northerly 5 to 8 knots after 18Z Tuesday.

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MARINE

Surface high pressure will remain situated offshore with lower pressure inland through much of the week ahead. Thermally induced low pressure expanding northward through Oregon will turn the flow more northerly later Tuesday into Thursday. Onshore flow will resume Thursday night into Friday as the offshore ridge is shoved eastward ahead of a weak frontal system arriving late Friday into Saturday. This will likely generate some wind and/or sea related headlines for portions of the coastal waters as well as the Strait of Juan de Fuca.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.