textproduct: Seattle/Tacoma

SYNOPSIS

A weak front will bring increasing clouds and cooler temperatures across Western Washington Friday into Saturday. Light rain chances also exist, particularly for portions of the mountains. Upper ridging will build back into the Pacific Northwest for warmer, dry conditions Sunday through Tuesday. Onshore flow increases again during the middle of next week.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

Mostly sunny skies across the area today with weak high pressure aloft. Temperatures will peak in the 70s for the majority of Puget Sound this afternoon, with cooler temperatures along the coast with continued onshore flow.

A weak front will move across Western Washington Friday through Saturday leading to increased onshore flow. Mostly cloudy conditions are expected on Friday, with a bit more in the way of partial sunshine late Saturday. In addition, light rain chances exist for the Cascades and Olympics, as well as from King County northwards Friday morning into Saturday. Rainfall amounts are expected to be light (if any), primarily less than 0.10". Temperatures will be a few degrees cooler both Friday and Saturday.

LONG TERM /SUNDAY THROUGH THURSDAY/

A large scale upper level ridge will build across much of the Interior Rockies and Central US early next week. Western Washington will be located on the northwest periphery of this ridge. This pattern will promote a warming trend, with dry conditions, Sunday through at least Tuesday. Minor HeatRisk is expected during this period, with a 10-35% chance of Moderate HeatRisk for Seattle metro southwards to Olympia. Uncertainty grows in ensembles by Wednesday with at least some indication of weak troughing developing offshore. This would allow for an increase in onshore flow mid next week with a slight cooling trend going into later next week. JD

AVIATION

VFR conditions prevail across all TAF sites this evening with west to northwesterly onshore flow continuing tonight. A stronger marine push is expected to develop by Friday morning, with likely MVFR/IFR ceilings as early as 05-09z spreading into the interior through the morning hours. This layer looks to stick around through the morning hours before dissipating around 20z-22z. NW winds this afternoon 4 to 8 knots will return to a more S/SW direction by early Friday morning.

KSEA...VFR conditions this evening will continue beyond sunset with a return of stratus cloud cover by early Friday morning. Latest guidance shows confidence in more widespread MVFR ceilings by 11z- 16z Friday as a marine layer spreads through the interior. Northwesterly winds this evening of 4 to 8 knots will turn southerly and generally remain the same speeds by early morning and continue through the day Friday. VFR conditions return around 19-22z.

MARINE

Surface high pressure remains over the coastal and offshore waters this afternoon. High pressure will weaken into Friday as a weak surface low shifts southward toward to just west of north Vancouver Island. An associated weak frontal system will cross the waters Friday afternoon into Friday night with little to no impact.

High pressure will rebuild Sunday into Monday. Diurnally driven increases in westerlies can be expected in the Strait of Juan de Fuca each the next several days.

Coastal seas remain 4 to 6 feet throughout much of the week.

Mazurkiewicz

FIRE WEATHER

The current onshore pattern will continue through the weekend which will lead to continued excellent nightly RH recoveries. Light drizzle or rain chances exist Friday into Saturday, mainly for the Olympics and Cascades. Rainfall amounts during this period would total less than 0.10". A ridge of high pressure briefly rebuilds into the region Monday and Tuesday. While the onshore pattern will largely remain in place, warmer daytime temperatures and clear skies will likely lead to RH values dipping into the 20-40% percent range, with the lowest values in the south interior and Cascades Valleys. This will allow fine fuels to continue to dry with elevated fire weather conditions.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 2 AM PDT Friday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.