textproduct: Seattle/Tacoma

SYNOPSIS

Moisture working its way up into the area from the south will result in chances for showers and isolated thunderstorms into Thursday. An upper level trough offshore will then push inland over the weekend, bringing cooler temperatures to the area and additional chances of showers. Troughing will persist through early next week, allowing for temperatures to trend just below to near normal.

SHORT TERM /TODAY THROUGH SATURDAY/

An upper-low continues to spin off the OR/CA coast early this morning - ushering moist, southerly flow aloft into the region. With it, showers and thunderstorms have been observed but coverage has waned overnight with loss of diurnal heating. For today, showers and thunderstorm chances are to continue as the upper-level pattern remains mostly unchanged. The aforementioned upper-low will persist offshore along with the Four Corners High in place, steering south-southwest flow aloft into western WA. Critical fire weather conditions is favored due to lightning from thunderstorm activity. Instability will be harder to come by compared to yesterday as onshore ushers in marine air. As a result, near- seasonal temperatures are in store with highs in the upper 70s to lower 80s across the interior. Coastal areas are forecast to remain in the 60s. Overnight lows will range between the mid 50s to near 60 F.

Drier conditions and a slight warm up are expected again by Friday as upper-ridging amplifies subtly. Onshore flow will allow for the marine stratus to push into the Sound by early Friday morning but will retreat back to the coast by the afternoon, allowing for highs across the interior to warm back into the mid 80s. Highs along the coast will remain cooler under the marine stratus- and only look to top out in the mid 60s to low 70s.

Guidance remains in good agreement that the upper level trough offshore will move across the area over the weekend, which will bring cooler temperatures and additional chances of showers to western Washington. The upper-low will begin to progress on Saturday. As it tracks inland, PoPs are favored to increase along the coast before spreading inland along the Cascades. Highs on Saturday are even forecast to top out slightly below average with highs in the 60s to mid 70s.

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LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

Upper level troughing looks to remain the dominant influence across the region over the weekend and into early next week. This will help promote continued onshore flow across the area and seasonal temperatures with highs in the 70s and lows in the 50s through Wednesday.

AVIATION

An upper level low will spin offshore today while sending mid level moisture and showers over western WA. Highest chances for thunderstorms will be over the Cascades with showers fading by 00-03Z this evening. Meanwhile, strong onshore flow in the lower levels will lead to low clouds and MVFR conditions this morning. Expect gusty SW winds to 20-25kt over the south sound through 16Z. 33

KSEA...Low clouds filling in this morning with MVFR conditions expected. Meanwhile, high-based showers will drift overhead through 18-21Z. SW wind around 10 kt. 33

MARINE

Onshore flow will prevail through the weekend with strongest winds through the Strait of Juan de Fuca. A front will stall offshore on Saturday then shift inland Sunday night. 33

FIRE WEATHER

Thunderstorm chances will remain into Thursday with the remnants of tropical storm Elida, which, given the warm and dry conditions, could cause additional ignitions from lightning. Rainfall from these storms will mainly be light. A Red Flag Warning was issued for the southern Cascades, South Sound, and Olympic Peninsula areas through Thursday night.

Increasing onshore flow beginning later Thursday will bring a wind shift with breezy southwest winds. This will also produce cooler temperatures and better overnight RH recoveries through the weekend into the first part of next week easing fire weather concerns. FELTON/JBB

SEW WATCHES/WARNINGS/ADVISORIES

WA...Red Flag Warning until 10 PM PDT this evening for Black Hills and Southwest Interior Lowlands-Central Coastal Lowlands- East Portion of the Olympic Mountains-North Coastal Lowlands-North and Central Coastal Strip-West Portion of the Olympic Mountains-West Slopes of the Central Cascades Generally above 1500 Feet.

PZ...Small Craft Advisory until 5 AM PDT Friday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 9 AM PDT this morning for Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.