textproduct: Seattle/Tacoma

SYNOPSIS

A ridge will bring dry and warm conditions through Friday. Wetter and cooler weather arrives on Saturday. Sunday remains cool with more wet weather headed our way on Monday. Another front may reach us midweek.

SHORT TERM /TODAY THROUGH SATURDAY/

High pressure and offshore flow will lead to dry and stable conditions across western WA today and Friday. Fog is forming across the lowlands this morning, especially in areas with calm winds, with pockets of dense fog expected. The fog will be shallow and burn off late this morning. Forecast highs will track warmer than normal with lower 70s expected. Areas near the water will be in the 60s. Offshore flow will peak overnight with gusty east winds along the Cascade crest and in the gaps (gusts to 20-30 MPH). Friday will be slightly warmer with interior temperatures reaching the mid 70s.

Saturday's weather will be cooler and wetter as the ridge shifts east and a front/trough move in from the west. Rain will mostly fall during the morning hours with highest chances of seeing wetting rains along the coast and north part. The Seattle area on south may only see a trace to a few hundredths. Onshore flow will increase Saturday afternoon with showers and a convergence zone over Snohomish County. 33

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

We're in between weather systems on Sunday but the air mass will remain cool. Sunday's morning lows will be in the 30s to mid 40s with temperatures near freezing across the south sound. Highs will be around 60 degrees. An upper low will spin offshore early next week keeping the weather cool and unsettled through Monday. The upper low will shift farther south on Tuesday for generally dry weather across western WA. Rain chances increase again on Wednesday as a weak front tracks down from B.C. 33

AVIATION

Areas of fog and low stratus bringing IFR to LIFR conditions are beginning to develop across portions of western Washington, most prolifically along and north of the metro area. Stratus and fog should continue to slowly fill in this morning. The biggest uncertainty is regarding the visibility--light north/northeasterly winds for some locations may allow for ceilings to remain a few hundred feet above the ground. Conditions should improve after 17-19Z this morning for mostly clear skies with high clouds through the remainder of the day. High cloud cover will persist tonight. High-res guidance is showing little to no development Friday morning, but NBM LAMP guidance is much more excited about development. Given the current discrepancy, will only introduce fog in the more prone locations for Friday morning at this time.

Winds remain north/northeasterly 5 to 10 kt through the period. Easterly winds will persist through the Cascades with gusts up to 20- 25 kt through the gaps this afternoon and into this evening.

KSEA...VFR early this morning, with IFR to LIFR cigs developing after around 11-13Z this morning. The biggest uncertainty will be with visibility as the winds may keep the vis higher than what is currently forecast. Stratus and fog look to scatter around 18-19Z followed by VFR conditions with high clouds through this evening. Fog/stratus development possible Friday morning but high clouds should keep it less widespread and guidance shows divergent solutions. Winds north/northeasterly 5-10 kt through this afternoon. Winds may turn east/southeasterly briefly as early as 20-22Z this afternoon, but more likely 00Z Fri through this evening before winds become more south/southwesterly Friday morning.

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MARINE

Areas of fog have are beginning to develop across the river valleys of western Washington and is expected to expand across portions of the interior waters. Will continue to monitor for fog development and the potential for any dense fog advisories. Light winds near the surface may be able to keep ceilings up just above the surface and limit fog potential.

Offshore flow will increase this morning as a thermal trough develops along the coast. Winds will peak this morning, but remain offshore through early Friday as the trough gets pushed inland by an incoming frontal system. This system will force winds to switch to onshore on Friday and increase Friday night into Saturday. The strongest winds will be most likely through the Strait of Juan de Fuca where there is a 35-45% chance of seeing up to low-end gale force gusts, but other locations such as the outer coastal waters and through Puget Sound and Hood Canal have 40-70% chances of seeing wind gusts over 20 kt. Winds look to decrease as the system departs Saturday evening. Winds look to remain relatively benign Sunday through early next week as systems are favored to pass by well offshore.

Seas remain 4 to 6 ft through tonight, increasing to around 8 to near 10 ft Friday through the weekend. The forecast gets more uncertain on Monday as a low pressure system moves through well offshore, but could generate and send larger waves to the coastal waters. The most likely forecast remains in the 8 to 10 ft range, but waves could get as large as 13 to 16 ft depending on the exact track of this system. EPS and GEFS show a 20-30% chance of seas exceeding 12 ft Monday into Tuesday.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...Dense Fog Advisory until 9 AM PDT this morning for City of Seattle-Downtown Everett / Marysville Area-Eastern Kitsap County-Lowlands of Lewis and Southern Thurston Counties- Lowlands of Pierce and Southern King Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties- Lowlands of Western Whatcom County-Olympia and Southern Puget Sound-Shoreline / Lynnwood / South Everett Area.

PZ...Dense Fog Advisory until 10 AM PDT this morning for Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.