textproduct: Seattle/Tacoma

SYNOPSIS

Increasing onshore flow will promote cooler and more moist conditions across the area Tuesday and Wednesday. Upper level ridge rebuilding Thursday with weak low level onshore flow will allow temps to start to warm again. Little change in the pattern Friday through the weekend though with greater uncertainty.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

Very warm conditions continue across much of western Washington this afternoon, despite the development of high clouds across the area. Farther north, however, thicker coverage of high clouds as well as developing onshore flow has helped keep their temperatures relatively cooler, with temps in the 60s and 70s, compared to upper 80s and low 90s from metro Seattle and southward. Areas along the coast will peak in the 70s and low 80s with developing onshore flow already this afternoon.

Pressure rises along the coast show that the thermal trough has shifted inland and will work its way east of the Cascades tonight. Onshore flow will continue to strengthen tonight, which will allow low temperatures to cool slightly compared to yesterday. Lows will range from the mid 50s to around 60 in the urban metro. The heat advisory will therefore expire tomorrow morning at 5 AM.

Stronger onshore flow will continue through much of the day on Tuesday. This will allow for temperatures to moderate up to 15-20 degrees compared to today, with highs in the 60s along the coast under marine stratus, and low to mid 70s across the interior. It will be noticeably breezy across much of the area, with the strongest winds expected through the Chehalis gap and the Strait of Juan de Fuca. Gusts 25-35 mph will be possible in these areas, up to 15-25 mph elsewhere. Expect a convergence zone to develop over the Puget Sound lowlands, but no precipitation is expected out of this. As winds decrease Tuesday night, this will allow for even cooler lows, down to the upper 40s to mid 50s.

Similar conditions on Wednesday; more stratus for the coast and west of Puget Sound but will burn off throughout the day. Highs in the upper 60s on the coast, with most of the interior in the 70s to near 80 in the Southwest Interior.

LONG TERM /THURSDAY THROUGH MONDAY/

Zonal flow will become more northwesterly as an upper level ridge begins to build offshore. This will allow for temperatures to start another brief warming trend Thursday and peaking on Friday. Highs look to top out in the upper 70s to upper 80s, with the warmest temperatures across the Southwest Interior. This will correlate to a Moderate level of HeatRisk on Friday for areas around the Seattle metro.

The range in uncertainty increases Saturday into early next week in terms of temperatures as the pattern gets more convoluted. The ridge remains onshore, with several shortwaves potentially moving through across the Pacific Northwest and a broad low moving into California. Then, a trough moves across from the north this weekend from B.C. into northeast Washington. Solutions without some of the shortwaves keep us warmer with weaker onshore flow; those with waves allow for stronger pushes and more moderate temperatures. The wave moving in from B.C. may allow for more unstable conditions to develop over the Cascades with very slight (15%) chances for showers and thunderstorms over the weekend. The National Blend is trending towards warmer solutions with highs in the mid 70s to low 80s.

62

AVIATION

West to northwest flow aloft will continue into Tuesday as an upper ridge over the region weakens in response to a weak upper trough moving onshore across British Columbia. Increasing low level onshore flow will likely bring MVFR ceilings to the coastal areas late tonight with VFR continuing across much of the interior. Gusty westerly surface winds can be expected near the coast as well as in and adjacent to the Strait of Juan de Fuca.

KSEA...VFR with variable amounts of high level moisture. Surface winds light west to northwesterly will back to southwesterly this evening and rise to 8 to 12 knots toward mid-morning Tuesday.

27

MARINE

Onshore flow has resumed over the coastal waters as the thermal trough has progressed inland. Northwesterly winds will increase late tonight into Tuesday over the coastal waters, reaching Small Craft Advisory conditions by mid-day Tuesday. These windy conditions will persist through the rest of the week. Seas will become locally-wind driven and become very steep. Wave heights will increase throughout the day Tuesday up to 10 to 13 ft with a dominant period of around 10 seconds. Waves in the outermost waters may reach up to 15 ft by late week.

Winds are beginning to strengthen through the Strait of Juan de Fuca at present and will continue to do so tonight, up to gale force for much of the day on Tuesday. Small Craft Advisory winds will also funnel down into Admiralty Inlet by Tuesday afternoon. Winds look to ease Tuesday night.

62

FIRE WEATHER

Strengthening onshore flow tonight into tomorrow will help to bring more moisture and cooler temperatures, easing fire weather concerns. Conditions dry out a bit again Thursday and Friday with minimum relative humidity values dropping into the 25-35% range despite no low level offshore flow. Temperatures will rise back into the upper 70s to low 80s in the lowlands. Breezy northerlies in the lowlands as well as westerly flow through the Cascades may pose elevated fire weather risks Thursday and Friday. Fuels will continue to slowly dry with no precipitation forecast through the weekend.

62

SEW WATCHES/WARNINGS/ADVISORIES

WA...Heat Advisory until 5 AM PDT Tuesday for City of Seattle- Downtown Everett / Marysville Area-Eastern Kitsap County- Eastside-Foothills and Valleys of Central King County- Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Snohomish and Northern King Counties-Foothills and Valleys of Thurston and Lewis Counties-Foothills and Valleys of the North Cascades- Foothills of the Western and Southern Olympic Peninsula- Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Lowlands of Pierce and Southern King Counties-Middle Chehalis River Valley- Northern Hood Canal-Olympia and Southern Puget Sound- Shoreline / Lynnwood / South Everett Area-Southern Hood Canal-Willapa and Black Hills.

PZ...Small Craft Advisory until 11 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning from 11 PM this evening to 11 PM PDT Tuesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 2 PM to 11 PM PDT Tuesday for Admiralty Inlet.

Small Craft Advisory from 11 AM Tuesday to 5 AM PDT Wednesday 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.