textproduct: Seattle/Tacoma

SYNOPSIS

An upper-trough will swing a couple of disturbances into the region Thursday through Saturday. Brief ridging is in the offing to begin next week but the pattern is forecast to reopen by Tuesday as additional troughing takes aim. A well-ogranized system looks to arrive around midweek with the potential for widespread rainfall. Cooler than average temperatures are favored throughout this time.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

The first of a series of upper-lows has swept through western Washington earlier today. Light shower activity has resulted along with breezy winds. Latest KATX/KLGX scans show shower coverage mainly over the coast, Olympic Peninsula and Cascade mountains along with a smattering over the southwest interior. 200-400 j/kg of surface based CAPE over the northern half of the CWA is being highlighted by HREF this afternoon. So with that, can't rule out a strike of lightning or two before the evening. Tonight, conditions are slated to trend drier as we'll be in between disturbances. Overnight lows are forecast to drop into the 50s.

Quasi-zonal flow aloft on Friday as models have the next impending upper-low looming off the coast of British Columbia. Mostly dry conditions during the day on Friday (barring a few showers) however, guidance have 850 mb winds converging over Puget Sound Friday night. A PSCZ is favored to develop around this time across both King and Snohomish counties with measurable rainfall a probability into the early morning hours on Saturday. The aforementioned upper-low is slated to arrive on Saturday morning as well with more widespread rain showers across western Washington. A 10-20% chance of thunder is in the forecast across the CWA with the highest probabilities over the Cascades. Precipitation will gradually dry out Saturday night as subsidence provided via transient ridging builds in to start the new week. Highs throughout the short-term ranging between the lower 60s to lower 70s with overnight lows in the 50s but can't rule out a few 40s in the southwest interior.

LONG TERM /SUNDAY THROUGH THURSDAY/

As mentioned, brief upper-ridging Sunday and Monday with drier conditions. Then, the next upper-trough will dig over the NE PAC and sit right off the PNW coast by Monday evening. Given latest guidance, it's associated upper-low will track south of the area into Oregon but we could get side swiped with showers on Tuesday. Then, a more organized disturbance is slated to arrive Wednesday and lead into Thursday. This feature has the potential to bring widespread rainfall and well-below average temperatures as the region will begin to get a taste of fall.

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AVIATION

Generally VFR this afternoon with areas of lingering MVFR in low clouds. Showers and isolated thunderstorm activity will continue to progress eastward across western Washington through the evening, mainly impacting the coastal terminals and terminals near the Canada border. Shower activity will produce localized MVFR conditions. Mid level clouds will stick around through the evening with continued VFR conditions, with another marine push overnight and residual moisture expected to bring in an expansive low stratus deck affecting most terminals early Friday morning. As a result, widespread MVFR to IFR is expected, with localized LIFR possible along the coast and over the Kitsap Peninsula. Breezy south to southwest winds will continue through the afternoon with gusts to 20 kt, with decreasing speeds overnight.

KSEA...VFR this afternoon with mid level clouds and breezy southwesterly winds with gusts to 20 kt at times. Conditions will calm into the evening, with increasing chances for MVFR conditions developing early Friday morning as low stratus expands over the Puget Sound. Improvement back to VFR expected by Friday afternoon, with light winds.

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MARINE

A weak frontal system will continue to move over the coastal waters today. Breezy south to southwesterly winds have picked up as a result, with localized gusts up to 30 kt in northern portions of the Hood Canal, producing wind waves up to 4 feet. As a result, a Small Craft Advisory has been issued through this afternoon. The strongest winds in this advisory will be in the Hood Canal area, though isolated SCA wind gusts elsewhere are possible through the afternoon.

Weak systems will continue to move over the coastal waters through the weekend, maintaining onshore flow and periodic westerly pushes through the Strait of Juan De Fuca. The westerly push Friday looks to reach Small Craft strength The push on Friday is expected to reach Small Craft strength, and a Small Craft Advisory has been issued. Another weaker westerly push is expected Saturday evening before winds become generally benign over area waters through the remainder of the weekend.

Seas will remain around 4 to 6 feet through the weekend.

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FIRE WEATHER

Onshore flow, cooler temperatures, and increasing RHs will persist into next week. There still remains an isolated threat for thunderstorms this afternoon and Saturday afternoon. For today, the threat is primarily over the Northern Cascades. As for Saturday, the threat expands from the Northern Cascades into the Central Cascades. Shall a thunderstorm develop, wetting rains are unlikely and lightning may pose a hazard that could lead to new fire starts. Additionally, thunderstorms could produce erratic and gusty outflow winds over existing fires. A weather system towards the middle of next week may bring wetting rains to the area.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 PM PDT this afternoon for Admiralty Inlet-Puget Sound and Hood Canal.