textproduct: Seattle/Tacoma

SYNOPSIS

A broad upper trough and onshore flow will continue to produce cloud cover and below normal temperatures across Western Washington throughout much of the week ahead. Weak weather systems passing through the trough will bring periodic chances of showers...especially over the mountains.

SHORT TERM /TODAY THROUGH TUESDAY/

The upper level low pressure system that brought showers to the area on Saturday continues to shift southeastward toward the Great Basin this morning. However, a broad upper trough will remain over the Pacific Northwest over the next several days. A series of nondescript disturbances will dip southward from British Columbia through midweek that will act to enhance onshore flow from time to time and produce just enough lift to squeeze out a few showers over mainly higher terrain. Temperatures will remain a little below average through the period.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

We're stuck in pretty much the same pattern as midweek arrives with a mean upper trough position parked over the Pacific Northwest. So, in sensible terms, it will likely be more of the same with mostly dry conditions outside of a few mountain showers and temperatures a smidge below average. As we approach the upcoming holiday weekend, the forecast picture begins to turn a little more uncertain. Ensembles are beginning to a show a trend toward a less amplified synoptic pattern along the west coast by Friday into the 4th. This would favor a return to temperatures closer to normal and generally dry conditions.

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AVIATION

An upper-level low will rotate through the Pacific Northwest through the period with western Washington under northerly flow aloft. A shortwave embedded in the northerly flow aloft slide through western Washington and Oregon Sunday evening he west side of the Cascades, potentially resulting in light drizzle at the coastal terminals. Majority of terminals still IFR/MVFR this morning, with improvement expected across the interior terminals after 19Z-21Z. Winds will be from the west-northwest 7-12 knots along the coast and from the west-southwest 6-11 knots across the interior. Breezy conditions this afternoon/evening from BFI southward, HQM, and Strait of Juan de Fuca, with gusts to 15-18 knots possible.

KSEA...Low MVFR/IFR ceilings expected to continue through at least 19Z Sunday, improving to VFR thereafter. Winds will remain from the south-southwest through the period with speeds 6-10 knots. Breezes up to 15 knots in the afternoon/evening.

MARINE

The dominant weather feature will involve broad high pressure over the Pacific and lower pressure over the interior that will promote onshore flow through the week. This will lead to gusty northwesterlies over the coastal waters and steep, choppy seas. In addition, the central and east portions of the Strait of Juan de Fuca will likely see diurnally driven increases in westerlies that may reach small craft advisory strength at times. The offshore ridge looks to weaken late this week for lighter winds and subsiding seas.

FIRE WEATHER

Little in the way of fire weather concerns remain in the picture well into the week ahead with upper troughing maintaining cool conditions, high RH, and periodic chances for shower activity. A trend toward more seasonable temperatures is indicated toward late week, but a significant warm and dry spell is not expected in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 5 PM this afternoon to 1 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 AM PDT Monday for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm- Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

Small Craft Advisory until 5 PM PDT Monday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.