textproduct: Seattle/Tacoma

SYNOPSIS

An upper level trough will produce varying amounts of cloud cover through the weekend along with near seasonal temperatures. High pressure will rebuild into the region Monday and Tuesday for a warming trend. A weak system may briefly cool temperatures around the middle of the coming week before a longer term dry and warm spell returns toward next weekend.

SHORT TERM /TODAY THROUGH MONDAY/

A upper level trough just offshore will send a series of weak disturbances across the area into early Sunday. For the most part, dry conditions will prevail though a couple light showers will be possible at times across the Olympic Peninsula, North Interior, and North Cascades. Temperatures through Sunday will hover within a couple degrees of seasonal normals for most spots. The upper trough will lift back into British Columbia later on Sunday as strong upper ridging centered over the Rockies and North Great Plains expands a little westward. With weaker onshore flow and modest height rises, temperatures on Monday will edge upward several degrees with plenty of sunshine.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

The dry and warm trend continues into Tuesday. Low level onshore flow will increase a notch or two which will cool coastal areas a bit, but interior temperatures will remain warm with areas around Seattle metro seeing a 30-50% probability of moderate HeatRisk.

Uncertainty remains in the temperature trend for the later half of the upcoming week as a number of ensemble members retain some degree of upper troughing just offshore. Based on the trends of the last few days, the main effect of this weak trough may be to simply delay an impending lengthy period of above normal temperatures that most guidance points toward commencing by next weekend.

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AVIATION

VFR conditions prevail across the airspace with mid-level BKN/OVC stratus around 5500-8000 ft across most of the region. Locations that haven't observed mid-level stratus are expected to see it form by 10-12z Sat. Guidance has only low to moderate confidence (20-45% chance) that stratus will deteriorate into MVFR/IFR cigs at most terminals except for along the northern Puget Sound and over terrain where confidence increases to 60-80%. If MVFR/IFR cigs do develop, it would be by 10-12z Sat, improving to VFR by 17-20z. Winds generally remain light and southwesterly, increasing to 8-10 kts after 18-21z Sat through around 06z Sun.

KSEA...VFR conditions prevail. Guidance indicates a 20-40% chance of MVFR ceilings developing 10-13z Sat. If they do manifest, a return to VFR by 18z is favored. Southwest winds continue below 8 kt. There are similar chances for stratus reforming around 10-12z Sun.

MARINE

A weak surface trough will remain over the offshore waters today before high pressure broadly rebuilds into the coastal and offshore waters Sunday and Monday and remains in place into midweek. This will promote a fairly typical summer pattern with varying degrees of onshore flow promoting a diurnally driven increase in westerlies through the Strait of Juan de Fuca nearly daily. Northwest winds over the coastal waters are likely to increase later Monday into Tuesday as thermally induced surface low pressure expanding over the interior of Western Washington tightens the onshore gradient.

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FIRE WEATHER

The current onshore pattern will continue through the weekend which will lead to continued excellent nightly RH recoveries. There's a 30-40% chance of rain showers today, mainly for the Olympics and northern Cascades, but rainfall amounts during this period would generally total less than 0.10". A ridge of high pressure 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. Some modest cooling is slated to arrive by the middle of next week, but may well be short-lived.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 3 AM PDT early this morning 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 PM this afternoon to 3 AM PDT Sunday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca.