textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge will bring warming and drying through the weekend. A weak system will cool things back down on Tuesday, with drier conditions and near normal temperatures through the rest of next week.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

The current forecast remains on track with no planned updates tonight. 33

Previous discussion...A weak shortwave moving over British Columbia will maintain light rain showers along the North Coast and Northern Interior through the afternoon today as high pressure builds northward into the region. Conditions across western Washington will dry out by this evening, with a warming and drying trend through the weekend as an upper level ridge continues to amplify. Clearing skies south of the Puget Sound may allow for cooler temperatures overnight tonight and the development of frost for cooler areas, and a Frost Advisory has been issued for Saturday morning. By Saturday afternoon, skies will become mostly sunny as low level flow turns offshore. An upper level low will begin to drop along the Canadian Coast on Sunday, introducing some high clouds across western Washington.

Temperatures will be the warmest of the year so far over the weekend, with highs reaching the mid 60s across much of the lowlands on Saturday, and temperatures increasing a few degrees into Sunday. Conditions will be warmest in the Cascade valleys and along the Cascade Foothills, along with the south Sound, where temperatures are favored to surpass 70 degrees. This introduces Minor (Yellow) HeatRisk for areas along and southward of the Puget Sound on Sunday.

LONG TERM /MONDAY THROUGH FRIDAY/

Warm conditions will continue on Monday as the upper level ridge breaks down and shifts eastward. Highs will peak once again in the upper 60s for most areas, with Minor HeatRisk once again for areas surrounding the Puget Sound and southward.

Onshore flow will resume Monday night into Tuesday as a trough pushes into British Columbia, with a marine push favored to bring low stratus and patchy fog inland Tuesday morning. Temperatures will cool off considerably with this trough, bringing highs back down into the low 50s. The same upper level trough will swing another front across western Washington on Wednesday, but conditions look to stay mostly dry with this frontal passage. Dry northwest flow is favored to continue into Friday, with temperatures returning to near-normal.

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AVIATION

Westerly flow aloft will continue into Saturday as upper ridging centered south of the region builds northward. High and mid level moisture associated with a dissipating frontal system will thin with time as subsidence with the upper ridge takes over. VFR will continue this evening across all terminals with mid and high clouds in spots. There is low confidence for lows clouds forming in the morning in some spots (would most likely be MVFR if they do form) but otherwise conditions will remain VFR through the TAF period. Winds will shift to the north this evening across the terminals, remaining 5 kt or less tonight, and increasing to 5-10 kt Saturday.

KSEA...VFR is expected through the TAF period. High and mid level clouds will thin with time and scatter out overnight. Probability for MVFR clouds Saturday morning remain low. Winds flipping to the west northwest this evening around 5 kt. Northerly winds will increase to 8 to 12 knots Saturday afternoon and evening.

27/HPR

MARINE

High pressure will build over the area waters today as a weak frontal system passes to the north and clips the northern coastal waters. High pressure will remain over the waters this weekend while a thermally induced trough expands northward along the Oregon coast. This will shift the flow northerly or weakly offshore. Onshore flow resumes early next week as a frontal system passes to the north. A strong westerly push is possible along the central and eastern Strait of Juan de Fuca Monday night into Tuesday.

Seas across the coastal waters will build towards 7-10 ft Tuesday into Wednesday.

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HYDROLOGY

No river flooding is expected over the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...Frost Advisory until 9 AM PDT Saturday for Foothills and Valleys of Thurston and Lewis Counties-Lower Chehalis River Valley-Lowlands of Lewis and Southern Thurston Counties-Middle Chehalis River Valley-Olympia and Southern Puget Sound-Willapa and Black Hills.

PZ...None.