textproduct: Seattle/Tacoma

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.

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AVIATION

Upper-level ridging has flattened and leading to quasi-zonal flow. West to west-southwest winds aloft with onshore in the lower levels. Patchy fog and low clouds are currently developing across the area so far this morning. This activity will become widespread cross the interior and portions of the coast with IFR/LIFR cigs and vis. VFR conditions are slated to return by 19-22z. An additional round of low clouds/fog is in store overnight Monday into Tuesday morning as low-level onshore flow persists.

KSEA...VFR as of 0930z but fog/low clouds will spread across the terminal by 12-14z with IFR/LIFR conditions and remain in place throughout the morning. VFR skies are to return by 18-20z and last for the remainder of the day. An additional round of low clouds/fog is in store overnight Monday night into Tuesday morning with continued low-level onshore flow. Light winds this morning before northerly this afternoon 4-8 kt.

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MARINE

Onshore flow has returned into today as low pressure shifts inland and surface high pressure builds offshore. However, the current SCA over the central/eastern strait will be allowed to expire this morning. 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.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.