textproduct: Seattle/Tacoma

SYNOPSIS

High pressure building overhead and weak offshore flow will maintain mild and dry conditions through the weekend. A system to the north will flatten the ridge by the beginning of next week, with near-zonal flow aloft and onshore flow at the surface maintaining seasonable conditions with morning clouds and afternoon sun breaks.

SHORT TERM /TODAY THROUGH MONDAY/

Stratus and fog continue to linger over the interior lowlands of W WA this morning while the coast has largely broken out with skies clearing there. Remainder of CWA should follow suit by early this afternoon. That said, inherited forecast remains on track an no need for morning updates at this time. For additional forecast details, please see Previous Discussion section below. 18

From Previous Discussion...As a weak frontal system continues to progress east of the Cascades, high pressure will continue to build over western Washington over the weekend. Weak offshore flow will develop this morning, helping to burn off a shallow marine layer expanding inland early this morning. Conditions across much of the lowlands will become sunny by the afternoon, with highs reaching the upper 60s to lower 70s. As high pressure aloft continues, offshore flow will limit a marine push early Sunday morning, with additional warming from a thermally induced surface trough bringing highs Sunday afternoon into the 70s for most inland areas away from the water. Areas along the Cascade foothills and valleys will inch closer to 80 degrees, with some areas along the Rainier Paradise corridor reaching the lower 80s.

The upper level ridge will flatten by Monday as a weather system moves inland over British Columbia, with near-zonal flow developing over the Pacific Northwest into early next week. This will bring a return to onshore flow, which will bring a stronger morning marine push of clouds inland and a return to more seasonable temperatures in the 60s to lower 70s.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

A flattened upper level ridge is favored to remain over the region through much of next week, maintaining near-normal temperatures and periods of morning clouds with afternoon sun breaks. Most areas will see high temperatures in the mid 60s to lower 70s, with a dry week on tap across western Washington. Ensembles continue to hint at a possible pattern change with wetter conditions developing by the end of next week, though confidence remains low over the timing as deterministic models continue to delay the onset of this potential next system. For now, expect dry, cloudy, and seasonable conditions with fairly little change day to day throughout next week.

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AVIATION

An upper-ridge is building across the region bringing west- southwesterly flow aloft. High cloud coverage is streaming overhead but not thick enough to discourage low clouds/fog development. As a result, LIFR/IFR fog/low stratus will continue this morning before conditions improve toward 19-20z to VFR as offshore flow increases. An additional round of low clouds/fog is in store overnight Saturday into Sunday morning.

KSEA...Surface wind will remain northerly through the period between 4-8 kt. IFR to LIFR stratus at the terminal with clearing to VFR around 19-20z. An additional round of LIFR/IFR stratus again likely into early Sunday morning.

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MARINE

Offshore flow is in store for this weekend as a thermal trough forms along the coast. Winds will turn onshore again Sunday night into Monday as low pressure shifts inland and surface high pressure builds offshore. Onshore winds will be strongest through the Strait of Juan de Fuca with Small Craft Advisory winds likely. Westerly pushes are favored throughout the upcoming week.

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SEW WATCHES/WARNINGS/ADVISORIES

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