textproduct: Seattle/Tacoma

SYNOPSIS

An upper ridge offshore will bring dry, warmer conditions on Wednesday. Troughing develops over the Pacific Northwest Thursday with an upper low bringing cooler conditions and precipitation potential into the weekend. More benign weather appears favorable into the beginning of next week.

SHORT TERM /TODAY THROUGH FRIDAY/

Mostly sunny conditions this morning with high clouds overhead and localized fog in river valleys. Transient upper- ridging today in concert with a surface thermal trough just off the PNW coast. As a result, dry conditions are favored as light offshore flow and subsidence rise temps into the upper 70s to lower 80s across the interior - slightly above average. Coastal areas are to stay put in the mid to upper 60s. Aforementioned ridging and surface thermal trough will push eastward on Thursday as the pattern progresses. Upper-troughing will develop as low-level flow switches onshore, ushering in marine stratus and cooler temperatures. Troughing further develops over the Pacific Northwest on Friday with a continued cooling trend. Ensembles are in general agreement that an upper low moves southwards offshore Friday with an increase of areas PoPs. Highs forecast in the 60s and 70s on Thursday before settling mainly in the 60s on Friday. Overnight lows in the 40s and 50s throughout the short term.

LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/

The upper-low will move inland over WA/OR during the weekend. Rain potential increases as the upper low moves inland, particularly Saturday into Saturday night. There is also a 10 to 15 percent probability for thunderstorms Saturday afternoon. Some uncertainty in the ensembles as to how quickly the troughing moves eastwards Sunday into Monday. However, lingering precipitation is likely at least over the Cascades on Sunday before a slow warming trend begins early next week with ridging offshore.

AVIATION

Flow aloft will remain primarily out of the west/northwest as a weak ridge moves east of the Rockies today, giving way to a trough tonight/Thursday. Most terminals are VFR this morning, with a couple isolated pockets of patchy pockets of low IFR/LIFR stratus affecting the primary Puget Sound terminals this morning, and just west of Bellingham. Widespread stratus has held off the coast. The patchy pockets will hang around through 16-17Z. Sky coverage today will primarily be VFR (outside of the patchy stratus this morning), with mid and high level clouds rolling in this evening ahead of the trough. The trough and increase of onshore will likely lead to some MVFR ceilings for most Thursday morning, forming from 12Z and potentially holding over through 21Z before improvement to VFR. The coast has a 30-40% chance of IFR conditions with the initial stratus onset, and a 20% chance of LIFR. Winds will remain northerly today at 5-10 kt, becoming 5 kt or less out of the west going into Thursday.

KSEA...Patchy LIFR stratus will hang over the terminal through 16- 17Z then improving to VFR through tonight (mid to high level clouds later this evening). 40-50% chance of MVFR stratus arriving Thursday morning from 12Z through as late as 21Z. North winds 5-10 kt today, becoming light out of the west Thursday at 5 kt.

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MARINE

High pressure will continue to build over the coastal waters through early Thursday, with a weak frontal system to the north bringing increased northwest winds over the coastal waters and a push through the Strait of Juan de Fuca. Westerly winds will reach Small Craft strength through the Strait late Wednesday evening through Thursday morning, and a Small Craft Advisory has been issued. Winds will gradually ease into Thursday night across all area waters. Another weather system is on track to cross the waters late Friday in to Saturday, but no significant impacts or headlines are anticipated at this time.

Seas around 4 to 5 feet will continue to gradually build into Thursday, reaching 8 to 11 feet across the outer waters. A Small Craft Advisory has been issued to account for these waves, which will be steep with a period of 8 to 10 seconds. Seas will ease to around 4 to 6 feet by Friday, with relatively calm seas into the weekend.

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FIRE WEATHER

A drying and warming trend will peak today, with light easterly flow through the Cascade gaps causing moderate overnight humidity recoveries along the western crest of the Cascades. Daytime relative humidities along the ridges of the Cascades and Olympics will bottom out in the low to mid 20s, causing brief elevated fire weather concerns for these areas. However, this will be short lived, with onshore flow returning on Thursday as a weak and mostly dry frontal system crosses to the north. Cooler and more moist conditions will return over the weekend, with periodic chances for light precipitation.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory from 11 PM this evening to 11 AM PDT Thursday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 AM Thursday to 5 AM PDT Friday 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.