textproduct: Seattle/Tacoma

SYNOPSIS

Cloudy skies and cooler temperatures will continue for the majority of this week with a broad upper level trough over Western Washington. Weak weather systems will move through the area throughout the week, bringing chances of showers primarily for the mountains. A warmer and drier pattern is favored to develop this weekend.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

A broad upper level trough will remain over the Pacific Northwest for the majority of the week, allowing weak disturbances to pass through the region. The majority of locations are expected to remain dry and the highest chances for showers will be limited to the mountains. Overcast skies in the morning and below normal temperatures this week, with temperatures generally in the 60s and low temperatures in the low 50s. May see some breaks in the clouds in the afternoon, but generally expect skies to remain fairly cloudy, especially along the coast. 29

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Cloudy skies and below seasonal temperatures will continue into the latter part of the week as long term guidance is in good agreement in keeping the broad trough over the Pacific Northwest through Thursday. A shift in the weather pattern is favored starting Friday as the majority of ensemble members highlight an upper level ridge building offshore in the Pacific. While there is uncertainty regarding the intensity of the ridge and axis location, the majority of members are in good agreement that Western Washington will be under the influence of a ridge this weekend. This will trend towards warmer temperatures and drier conditions. 29

AVIATION

Latest obs show largely low-end VFR (less than 7 kft) conditions across the Sound, northern inland, and Strait of Juan de Fuca terminals with stratocu and high clouds increasing westward overhead. Elsewhere, MVFR conditions are seen across the coast. Latest satellite and obs continue to show northwesterly onshore flow with MVFR conditions starting to penetrate inland of the southern interior with some obs and web cams showing this trend over the last two hours (KOLM and KTCM). Current thinking is there is a high chance for MVFR ceilings (>75%) with various systems (NBM, HREF, REFS) supporting this outcome. Confidence is bolstered by moisture evolution in cross-sections with modest upslope flow and isentropic ascent in deterministic guidance from 03Z-12Z across the interior. There is potential for IFR as well for Puget Sound terminals with these condition seen last night/this morning as well. Otherwise, improvement to VFR for interior terminals anticipated between 21Z- 00Z, except sub-VFR conditions prevailing along the coast.

KSEA...VFR ceilings in place with conditions anticipated to deteriorate early this morning to MVFR, current thinking is 8-10Z. Moderate confidence for development of IFR ceilings as well (50-70%) within the window of 11-14Z. Winds should remain light breezy, and sufficient turbulence and cloud cover should keep fog risk low. Southwesterly winds generally 6-9 kts in the TAF period with gusts expected to be limited/infrequent over the next 36-hrs. ET

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. A small craft advisory is set to go into effect this evening. Wednesday looks to be the next strongest push, with probabilities around 45-65% of winds exceeding 21 kt. 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 until 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 Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.