textproduct: Seattle/Tacoma

SYNOPSIS

Weak warm front will brush the northwest corner Wednesday. Another system moving over the top of an offshore ridge moving through Thursday. A series of stronger and wetter systems will take aim at Western Washington beginning Friday and continuing through the middle of next week.

SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/

The short term pattern is dominated by strong high pressure offshore, with moist NW flow over western WA. We're looking for mainly dry weather tonight and Wednesday (the driest day over the next 7) although the low level air mass will remain moist for low clouds and fog. The forecast is wetter heading into Thursday as the next wave of moisture overrides the ridge and moves into the region. This moisture tap is aimed particularly over the central Cascades for mountain rain and high elevation snow, potentially sending a few rivers in King and Snohomish counties into Action Stage. 33

LONG TERM /FRIDAY THROUGH TUESDAY/

The pattern remains active through the extended period as wave after wave of moisture streams through western WA. The main concern will be focused toward river levels with potential threats of flooding as we head through early next week. Without much of a break, the landslide threat will also be elevated due to saturated soils and antecedent conditions. The air mass will be mild with temps in the 40s and 50s, and high snow levels. Stevens Pass may see periods of light snow with all rain down at Snoqualmie Pass.

In addition, high astronomical tides will be observed through this same period with potential for minor coastal flooding (both coast and interior). 33

AVIATION

Northerly flow aloft as an upper level ridge begins to build offshore. A mixed bag of ceilings from earlier this morning has continued to lead to MVFR/IFR ceilings this afternoon. Some improvement is looking likely later this evening as some terminals remain around MVFR/low-end VFR. Conditions look to lower once more overnight and into Wednesday morning with some patchy fog possible. With patchy fog and lowered ceilings, will see a mix of MVFR/IFR conditions across most interior terminals generally around 08-14z. Northerly winds this afternoon 6 to 8 knots will decrease generally around 3 to 6 knots and turn more NE.

KSEA...MVFR conditions this afternoon. Conditions may improve slightly to low end VFR later this evening at times, with guidance split on keeping MVFR through overnight hours. Conditions will lower again overnight and early Wednesday morning with the possibility of fog near the terminal, which could bring IFR conditions (30% chance) through 16z. Conditions look to hold steady at MVFR/VFR by Weds afternoon. Northerly winds this afternoon 7 to 9 knots will turn NE after 00z and remain around 3 to 6 knots.

Mazurkiewicz

MARINE

Surface high pressure offshore will continue to bring benign conditions to the area waters this evening. Winds and seas will start to become elevated on Friday as a series of systems will start to approach the area waters, likely bringing small craft advisory gusts to the coastal waters along with a push down the Strait of Juan De Fuca. Active weather continues throughout the weekend and into the first half of next week with elevated winds and seas.

Combined seas around 8 to 10 feet this afternoon lowering to 4 to 6 feet overnight. Seas look to get up around 10 feet late Friday night, generally staying that way throughout the weekend. Seas look to build more rapidly 10 to 13 feet by Monday.

Mazurkiewicz

HYDROLOGY

The series of weather systems forecast to reach the area will eventually increase the threat of river flooding in the coming days. West northwesterly flow aloft with the system Friday puts the area of greatest precipitation in the North Central Washington Cascades. Snow levels rising over 6000 feet. Current forecast 18 hour precipitation amounts between 06z Friday and 00z Saturday have an area of 2 inch bullseyes between Snoqualmie Pass and Glacier Peak. This will put pressure on the rivers flowing out of this area including but not limited to the Snoqualmie, Skykomish, Snohomish and Tolt rivers.

As the flow aloft becomes more west southwesterly the flood threat will shift to the flood prone Skokomish River later in the weekend.

Plenty of uncertainty on how the pattern will set up early next week but there is a chance for a widespread river flooding event.

The landslide threat is minimal the next few days. The series of systems will eventually take its toll with the landslide threat increasing this weekend into early next week. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 10 PM PST this evening 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.