textproduct: Seattle/Tacoma

SYNOPSIS

An upper ridge will remain over Western Washington through Tuesday bringing dry, warm conditions. Upper low approaches the area midweek for the return of onshore flow, cooler temperatures, and chances of precipitation. Upper troughing will continue to influence the region into next weekend maintaining cooler, cloudier conditions.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

Upper ridging continues to build into the Pacific Northwest today, with mostly clear skies and warming temperatures. North winds exist at the surface with more east flow aloft in the mid levels. The east wind component aloft is allowing for wildfire smoke from the Cascades to drift into Western Washington this afternoon. This will continue through midday Tuesday. Onshore flow resumes later Tuesday, which will push the smoke eastwards outside of the area by Tuesday night. Otherwise, temperatures will peak on Tuesday with the ridge axis over the interior Pac NW, with highs in the 80s to low 90s over Puget Sound, warmest temperatures in the Cascade Valleys. Moderate HeatRisk is expected Tuesday for the interior.

An upper low approaches Western Washington on Wednesday, leading to cooler temperatures and more widespread morning stratus. Additionally, flow aloft will become more south-southwest, and will need to monitor the slight chance for thunderstorms in the North Cascades during the afternoon. Temperatures drop into the 70s to low 80s Wednesday, with 60s along the coast.

LONG TERM /THURSDAY THROUGH MONDAY/

Upper troughing moves across the Pacific Northwest Thursday, resulting in rain potential for portions of Western Washington, along with cooler temperatures. Ensembles suggest another trough moves southwards out of British Columbia overhead late Friday into Saturday for additional QPF chances and reinforced onshore flow. Onshore flow then continues early next week. Temperatures are expected to be below normal during this period, with highs only in the mid 60s to mid 70s. JD

AVIATION

Southwest flow aloft across western Washington with light low level offshore easterly to northeasterly flow. Widespread VFR conditions are expected through the evening today, with some haze aloft from area wildfires. Another round of marine stratus is expected along the coast early Tuesday morning with valley fog and shallow stratus expanding inland. This marine push is expected to be more limited than Monday morning, and may not make it east of the Puget Sound. N/NE winds this afternoon around 8 to 12 knots, easing around 08Z then becoming light southerly around 14-15Z for many locations south of the Strait of Juan de Fuca and Skagit County.

KSEA...VFR conditions through the afternoon and evening hours. North to northeast winds through the afternoon, generally around 8 to 12 knots then becoming light southwesterly around 14/15Z. Stratus and or shallow fog not expected at the terminal into Tuesday morning. Valley fog may be near, developing again to the east during the early morning. A shift to southwesterly winds in the morning may help keep the terminal clear. LAMP guidance still indicating around a 15% chance of ceilings less than 500ft by 13z Tuesday morning, this will be something to keep an eye on overnight.

MARINE

Surface high pressure remains over the coastal waters into Tuesday. North winds will increase along the coastal waters this afternoon and evening, with periodic Small Craft Advisory wind gusts. A thermal trough along the coast will slide inland on Tuesday, with increasing onshore flow into Wednesday. A westerly push is expected through the Strait of Juan de Fuca Tuesday evening. Probabilities for SCA wind gusts in the Strait during this period range 60 to 90%, and for this reason a Small Craft Advisory has been issued. Otherwise, winds transition to the south and southwest for all waters midweek. Onshore flow then continues through late week, with periods of stronger west winds through the Strait of Juan de Fuca.

Seas of 4 to 6 feet for the majority of the week. Seas may be choppy through this evening for the coastal waters due to a period of around 6 seconds. JD

FIRE WEATHER

A warming and drying trend will continue through Tuesday as a thermal trough builds northward along the coast. Offshore easterly flow will strengthen tonight into Tuesday, promoting additional drying near the Cascade gaps, where relative humidity values are expected to drop to near critical values in the low to mid 20s on Tuesday. Elevated fire weather conditions will continue through Tuesday for these areas.

A pattern change late Tuesday into Wednesday will bring the return of moist onshore flow, cooler temperatures, and chances of light precipitation through the remainder of the week, mitigating fire weather concerns for most areas. Isolated thunderstorms along the coast and over higher terrain are possible with each round of moisture, though the exact details remain somewhat uncertain.

Upper level troughing is favored to remain over the Pacific Northwest over the weekend, with continued onshore flow, excellent overnight relative humidity recoveries, and cooler temperatures. Chances for thunderstorms continue into the weekend, with around a 15-25% chance across both the mountains and lowlands.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 5 PM Tuesday to 2 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until midnight PDT tonight 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.