SeaTac, WA 98158 Weather

Synopsis

An upper low will continue to linger over Western Washington through Friday for periodic showers in the lowlands, light snow shows in the mountains, and cooler temperatures. Conditions will trend drier over the weekend with temperatures remaining cool, especially overnight.

Short term

Little change in the pattern overnight and the current forecast remains on track. 33

Previous discussion: An upper level low continues to hover offshore maintaining showers around western Washington this afternoon. Cooler temperatures in the low 50s within the post frontal airmass. Additionally, there is chance (15-20%) of a thunderstorm or two late this afternoon due to the unstable environment. Thunderstorm chances greatly decrease early evening as the sun sets. Snow showers continue in the Cascades but has greatly decreased in coverage since this morning, and will continue as the Winter Weather Advisory remains out until 5PM. Most of the accumulations will be in and around Mount Rainier.

The aforementioned upper level low will not move much into Thursday and Friday, keeping scattered showers around in the lowlands and light snow accumulations in the Cascades. Overall precipitation will trend downwards, but can't rule out stray showers at times with most of the area remaining somewhat dry. Afternoon temps in the low to mid 50s.

Long term

Ensembles are agreeing in the low weakening into the weekend, with conditions becoming drier over western Washington. There may be a shower or two in the Cascades, but overall most of the interior looks to be dry over the weekend with high temperatures in the mid 50s. Overnight lows look to become cooler in the low to mid 30s, with some locations even seeing mid to upper 20s, particularly in the Southwest Interior. Weak ridging will allow conditions to likely remain dry heading into midweek.

Mazurkiewicz

Aviation

An upper level trough will remain just offshore of Western Washington into Thursday producing southwest flow aloft. The air mass is somewhat unstable. Showers will continue across the region: most numerous near the coast. With low level winds easing overnight, areas of MVFR ceilings are expected to form toward daybreak before lifting again Thursday afternoon.

KSEA: A general decrease in shower activity is expected overnight with most activity south and west of the terminal. As surface winds ease somewhat overnight, an general lowering of ceilings is expected with periods of higher end MVFR 12Z-18Z before lifting back to VFR Thursday afternoon. Surface winds E/SE easing to 5 to 7 knots this evening and continuing into Thursday morning.

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Marine

Seas have peaked across the coastal waters earlier this morning, but remain quite steep with dominant periods around 8 to 9 seconds. As a result, a small craft advisory remains in effect for these areas through the evening. Expect both the seas to decrease and the dominant period to lengthen, so this should be good to expire by the end of the night. Elsewhere, conditions on the Grays Harbor bar are expected to worsen around a very strong ebb this evening as seas steepen and build, so an advisory has been issued here as well.

Looking ahead, seas will likely build early next week back to around 10 ft with the arrival of a long period swell into the coastal waters.

Watches, warnings and advisories

WA: None. PZ: Small Craft Advisory until 9 PM PDT this evening for Grays Harbor Bar.

Small Craft Advisory until 11 PM PDT this evening 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.