textproduct: Seattle/Tacoma

SYNOPSIS

A very active week ahead with a parade of weather systems keeping conditions warm, wet, and windy from Thursday and beyond. A more significant atmospheric river system event looks to set up early next week with the potential for flooding. Coastal flooding impacts will be possible Friday into early next week but look to remain mostly minor.

SHORT TERM /TODAY THROUGH FRIDAY NIGHT/

Cool, cloudy and mostly dry conditions will continue through this evening. Temperatures right around 45 degrees across the area will drop a bit into the upper 30s to low 40s tonight. There could be some isolated patchy fog given the light winds that will continue tonight. A frontal system will move across the area on Thursday that will bring a decent push of rainfall across the entire area. Up to half an inch of rainfall across most of the lowlands and over an inch in the mountains will be possible on Thursday. The associated surface low is pretty weak so while north/northwesterly winds return across the area, they will remain fairly weak. Highs in the mid 40s.

Flow turns westerly aloft allowing for the next frontal system to move across the area Thursday night into Friday. This will permit a more significant round of rainfall, with a couple of inches of rain possible across the mountains, around an inch along the coast, and lesser amounts through the interior. Winds will increase across the interior, but remain below advisory thresholds, with peak gusts in the 25-35 mph range. This will also be a warmer system, with highs in low to mid 50s and snow levels rising to around 5000-6000 ft.

Tide levels will increase Thursday and Friday across the area. Fairly minor impacts are expected on Thursday for the coast, with the potential for more significant impacts on Friday with a higher tide, stronger onshore flow, and slightly larger waves. The impacts, however, will not be as significant as the coast saw in November. Tides peak on Friday along the coast then through the interior this weekend, where additional minor coastal flooding may be observed.

LONG TERM /SATURDAY THROUGH TUESDAY/

Rain will continue into Saturday as the aforementioned system moves through the area Friday night and substantial onshore flow continues. Snow levels will briefly low Friday night into Saturday back down to around 4000 ft, which may allow for a brief but good shot of accumulating snow at Stevens Pass. There is a 45% chance of seeing at least 6" of snow at the pass through Saturday afternoon. Models are hinting at a bit of a break in the precipitation Saturday evening until another, albeit relatively weak and progressive, system moves through Sunday. Snow levels will rise back up against 5000 ft. The focus then turns towards Monday and trough the beginning of next week as it's looking likely that a significant atmospheric river is going to take aim at western Washington. There remains differences, mainly at how long duration this system is going to persist over the area. There remains some uncertainty to exact amounts, but on the order of several inches of rain are possible across the entire area. More details about river flooding are detailed in the hydrology section. Winds will begin to pickup once again, and warmer temperatures will return, back into the mid 50s. Snow levels rise back up to 6000 ft.

High tides will peak across the interior waters on Saturday, but high tide levels will linger into the the beginning of next week, with minor coastal flooding impacts possible across portions of the entire Washington coastline through this time period.

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AVIATION

Northwesterly flow aloft with a warm front approaching offshore. Mixed bag of ceilings (VFR to IFR) continue as limited low level flow keeps lower ceilings in place. Some minor improvement to low end VFR is possible across portions of the interior this afternoon. Conditions will start to lower overnight to MVFR/IFR especially by Thursday morning as the aforementioned warm front crosses the area. Rain could lower visibilities at times during the morning to 4-6SM. Light and variable winds this afternoon will start to take a southerly component around 06z and remaining around 4 to 6 knots.

KSEA...VFR this afternoon will start to lower to MVFR later this evening. An approaching warm front will spread rain showers late tonight through early Thursday morning, possibly bringing vsbys down at times. Conditions will lower to IFR (10z-17z) as the rain comes in. Ceilings will remain MVFR/IFR through the afternoon as lingering moisture keeps the ceilings low. Light and variable winds will turn southerly overnight and remain around 4 to 6 knots.

Mazurkiewicz

MARINE

Surface high pressure will dissipate later this evening allowing for a front to cross over the area waters with no notable impact for the coastal waters.

A stronger front will approach the coastal waters on Friday, for likely small craft advisory strength winds for the coastal waters. A westerly push down the Strait of Juan De Fuca will initially start off at small craft strength, but latest guidance indicates the potential for gale strength gusts - will be something to continue to monitor. Additional systems will cross over the area waters over the weekend, with a much stronger system crossing the area early next week, which could yield headlines for all of the interior waters.

Combined seas 6 to 8 feet this afternoon will gradually build up to 10 to 12 feet by Saturday. Seas will decrease below 10 feet on Sunday but will build up above 10 feet by late Monday.

Mazurkiewicz

HYDROLOGY

A series of wet weather systems forecast to reach the area will eventually increase the threat of river flooding this weekend, especially into the first half of next week. West to northwesterly flow aloft with the system on Friday will put the area of greatest precipitation in the North Central Washington Cascades. Snow levels, at this time, will be rising over 5500 to 6000 feet.

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

There's still a wide variance in the possible precipitation amounts with an atmospheric river setting up through the first part of next week. It is still within the realm of possibility that we could have a widespread river flooding event on our hands beginning next Tuesday/Wednesday, with multiple rivers reaching minor and moderate flood stages. There is still so much uncertainty with the exact flood levels and stages and this will change over the next couple of days.

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

Felton/Mazurkiewicz

SEW WATCHES/WARNINGS/ADVISORIES

WA...Coastal Flood Advisory from 9 AM to 3 PM PST Thursday for Grays Harbor County Coast.

Coastal Flood Watch from Friday morning through Friday afternoon for Grays Harbor County Coast.

PZ...None.