textproduct: Seattle/Tacoma

UPDATE

No changes made to the inherited forecast. The previous discussion remains below along with an updated aviation section.

SYNOPSIS

Upper level ridge over the area today shifting east tonight. Thermally induced surface trough near the coast this morning will move inland this afternoon and east of the Cascades tonight. Increasing low level onshore flow Wednesday. First weather system in a couple of weeks approaching the coast Thursday. Front reaching the coast Friday morning moving east of the Cascades by Friday evening. Cool upper level low dropping down over the area Saturday. Low moving east Sunday with weak upper level ridge beginning to build offshore. Weak upper level trough moving through Monday.

SHORT TERM /TODAY THROUGH THURSDAY/

Satellite imagery shows stratus right along the beaches central and south coast with a few high clouds moving through the area. Temperatures at 3 am/10z were in the mid 50s to lower 60s except mid to upper 60s in the Seattle area.

Upper level ridge over the area today. Thermally induced surface trough near the coast will drift slowly east this afternoon maintaining low level offshore flow. 850 mb temperatures rising to plus 16C to 18C this afternoon. Highs warming into the 80s with the warmer locations like the Southwest Interior and Cascade Foothills reaching the lower 90s. Afternoon seabreeze kicking in along the central coast keeping highs in the 70s right along the beaches. Best chance for a record high today will be at Bellingham.

Upper level ridge moving east of the Cascades tonight. Thermally induced surface trough also moving moving east of the Cascades tonight. Low level flow turning onshore along the coast with light low level flow over the interior. Lows tonight in the mid 50s to lower 60s. Record high minimum temperatures will be possible over the interior.

Blend has high temperatures Wednesday just a degree or two lower than Tuesday. Thermally induced trough east of the Cascades with low level onshore flow to start the day increasing in the afternoon. Upper level ridge also east of the Cascades with temperatures aloft cooling. 850 mb temperatures in the plus 14C to 16C range in the afternoon. Winds in the lower levels also turning westerly Wednesday morning. Stratus remaining confined to the coastline but flow aloft turning west southwesterly pushing some high clouds cover through the area. All these variables add up to a cooler day Wednesday with highs 5 to 10 cooler than Tuesday, in the mid 70s to mid 80s for the interior. More cooling along the coast with stronger onshore flow. Highs on the coast in the mid 60s.

Onshore flow increasing Wednesday night with surface high pressure building offshore ahead of an approaching weather system. High clouds continuing to move across the area with stratus moving inland late. Lows in the 50s.

Front approaching Thursday. Rain out ahead of the system could reach the coast as early as the afternoon hours. Thickening cloud cover will keep highs in the 60s and lower 70s.

Heat advisory remaining in effect for all the lowlands except the coastal beaches today. Cooling Wednesday will drop the inland coastal areas and the Northwest Interior out of the advisory. Heat advisory coming to an end for all locations Wednesday evening. Felton

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

Rain spreading inland Thursday night. Front reaching the coast Friday morning with the front east of the Cascades by late Friday afternoon. Rain turning to showers behind the front with breezy conditions. Post frontal air mass somewhat unstable for a chance of thunderstorms as well. Convergence zone setting up probably over Snohomish county in the afternoon and evening hours. Models are a little weaker with the southerly surface gradients which brings up the possibility the convergence zone could end up a little further south over Northern King County.

Cool upper level low dropping down over the area Friday night into Saturday keeping showers in the forecast. Weak upper level ridge building offshore Sunday. Weak upper level trough moving down the backside of the ridge into Western Washington Monday for a chance of showers.

High temperatures in the upper 50s to mid 60s Friday and Saturday and only in the 60s Sunday and Monday. There is a chance for record low maximum temperatures Friday and possibly Saturday. Felton

AVIATION

Primarily VFR conditions are expected with passing high clouds through the forecast period. There is moderate confidence (50-60% chance) for IFR conditions to return at HQM Tuesday evening through Wednesday morning. Winds will generally be out of the north 5-10 knots for interior terminals and more variable in direction for the coastal terminals.

KSEA...VFR expected through the TAF period. Northeast winds this morning 5-8 knots back to the northwest 8-10 knots in the late morning and early afternoon. Winds become more northerly 6-10 knots Tuesday night. A return of broader onshore flow on Wednesday will shift winds to the west-southwest sometime Wednesday morning between 10-14Z.

MARINE

Thermally induced surface trough near the coast will drift slowly east this afternoon moving east of the Cascades tonight. Low level flow turning onshore along the coast with light low level flow over the interior. With the thermally induced trough east of the Cascades low level onshore flow to start the day Wednesday increasing in the afternoon and evening. A gale watch has been issued for the Central and Eastern Strait of Juan de fuca for Wednesday night. Onshore gradients easing Thursday. Frontal system moving through the waters Friday with possible small craft advisory winds with and just behind the front. Winds easing Saturday.

Choppy seas developing over the outer coastal waters tonight with swell 7 to 9 feet with a 7 to 9 second period. The choppy seas will continue over the outer coastal waters through Wednesday night. Felton

FIRE WEATHER

High pressure aloft combined with a thermally induced surface trough over the area will create elevated fire conditions today. In addition to the warm, dry, and conditionally unstable air mass, low level offshore flow will drop minimum relative humidity values into the twenties, and even the teens this afternoon. The upper level ridge and thermally induced trough moving east tonight but elevated fire weather concerns could linger into Wednesday. Fuels are approaching critical levels, but the main concern remains dry grasses or shrubs, or dead piles of fuels where brush fires may be able to start (as seen the last few days). Onshore flow will return with improved low level moisture Wednesday night and Thursday. Weather system moving into the area will bring a chance of wetting rains for the first time in a couple of weeks Thursday night and Friday. Cool weather will continue through the weekend. Felton

SEW WATCHES/WARNINGS/ADVISORIES

WA...Heat Advisory until 11 PM PDT this evening for Eastern Strait of Juan de Fuca-Foothills and Valleys of Thurston and Lewis Counties-Foothills and Valleys of the North Cascades-Foothills of the Western and Southern Olympic Peninsula-Island County-Lower Chehalis River Valley- Lowlands of Lewis and Southern Thurston Counties-Lowlands of Western Skagit and Northwestern Snohomish Counties- Lowlands of Western Whatcom County-Middle Chehalis River Valley-Northern Hood Canal-Olympia and Southern Puget Sound-Port Townsend Area-San Juan County-Southern Hood Canal-Willapa and Black Hills.

Heat Advisory until 11 PM PDT Wednesday for City of Seattle- Downtown Everett / Marysville Area-Eastern Kitsap County- Eastside-Foothills and Valleys of Central King County- Foothills and Valleys of Pierce and Southern King Counties-Foothills and Valleys of Snohomish and Northern King Counties-Lowlands of Pierce and Southern King Counties-Shoreline / Lynnwood / South Everett Area.

PZ...Gale Watch from Wednesday evening through late Wednesday night for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 6 PM this evening to 6 AM PDT Thursday 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.