textproduct: Seattle/Tacoma

SYNOPSIS

An upper ridge will shift east tonight. A front will move across the area on Saturday, with increasing onshore flow into Sunday. Upper level ridging builds offshore Sunday night and moves over Western Washington on Monday. The ridge will remain in place through at least midweek for dry, warm conditions.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

Mostly sunny skies across Western Washington this afternoon with temperatures in the 70s to low 80s. High pressure will move east of the Cascades into tonight ahead of a frontal system. The front moves across the area on Saturday, resulting in increased light rain, especially for the Olympic Peninsula, Cascades, and from Snohomish County northwards. There is also a 10-20% chance for thunderstorms over the northern Cascades Saturday afternoon. In addition, winds will be rather breezy in a post-frontal airmass, with west wind gusts ranging 15 to 25 MPH (with localized gusts to 30 MPH) on Saturday.

Onshore flow continues post-front later Saturday into early Sunday, resulting in the development of weak convergence over Snohomish County and vicinity. Light rain may continue at times into Sunday morning for this region before drier conditions return by Sunday afternoon. Upper level ridging then begins to build offshore by Sunday night. Temperatures will be quite a bit cooler this weekend, with highs only in the mid 60s to mid 70s.

LONG TERM /MONDAY THROUGH FRIDAY/

The upper level ridging continues to build over Western Washington early next week, resulting in drier, warming conditions. Widespread Minor HeatRisk is expected Monday, with areas of Moderate HeatRisk Tuesday and Wednesday. Upper level flow also transitions more northeasterly on Monday, which may result in increasing wildfire smoke into midweek, this continues to be monitored. Some uncertainty exists in ensembles by later next week in regards to the ridge flattening a bit for a slight cooling trend. Either way, continued dry conditions are expected through late week. JD

AVIATION

Southwest flow aloft will increase tonight as a weak frontal system approaches from the west and pushes inland Saturday morning. Ceilings will lower to MVFR along the coast late tonight then spread inland across the interior lowlands early Saturday morning. Gusty post-frontal west to southwesterly surface winds are expected at times on Saturday and a convergence zone is expected to develop later Saturday afternoon into Saturday night.

KSEA...VFR will continue into this evening. Ceilings are expected to lower to MVFR near or after 12Z Saturday and persist into at least early afternoon. Surface winds west to northwest 6 to 10 knots will back to southerly overnight and rise to 10 to 15 knots with gusts to 20 knots by mid-morning Saturday before easing late in the day.

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MARINE

A weak frontal system will reach the waters tonight and Saturday. Increasing onshore flow will lead to small craft advisory westerly winds in the central/east strait late this afternoon and evening and again much of Saturday. Additionally, post-frontal onshore flow will lead to small craft advisory southwesterlies in Puget Sound/Hood Canal during the day on Saturday. High pressure will rebuild over the coastal waters Sunday and remain in place into early next week as thermally induced low pressure expands northward across the interior.

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FIRE WEATHER

Elevated fire weather concerns will continue today as a warming and drying trend peaks. Relative humidities will drop into the upper 20s and 30s over portions of the western Cascades and lowlands south of the Puget Sound, though an approaching system will bring onshore flow tonight with healthy overnight humidity recoveries.

A frontal system will cross western Washington Saturday morning, bringing a chance of wetting rain to the northern Olympic Peninsula and North Cascades, alongside breezy winds area-wide and increased onshore flow. Ridgetops in the Cascades will see wind gusts of 30 to 40 mph Saturday afternoon, though incoming cooler and wetter conditions will prevent humidities from reaching critical levels. In addition, the North Cascades will see a 20% chance of thunderstorms developing midday Saturday, though widespread lightning is not expected with this system.

A ridge will build over the western US during the first half of next week, bringing additional warming and drying to the region. Minimum relative humidity values will drop into the 20s and 30s for most inland areas, bringing elevated fire weather concerns. Surface flow is also expected to turn offshore, though flow will be fairly weak. Northerly and easterly winds at times may bring in smoke from wildfires across eastern Washington and British Columbia.

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SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 7 PM PDT Saturday 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 to 7 PM PDT Saturday for Puget Sound and Hood Canal.