textproduct: Seattle/Tacoma

SYNOPSIS

Weak upper-low off the Oregon coast moving southward tonight. Upper level ridge building into the British Columbia coast Sunday will progress over western Washington by Tuesday. Ridging will vary in intensity through midweek before exiting on Friday. Temperatures remaining above average through much of the upcoming week.

SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/

An upper-ridge is nosing into British Columbia as an upper-low floats off the coast of Oregon and NorCal. This low center has been responsible for showers and thunderstorms across the Oregon Cascades earlier today. A slight chance (15%) of thunderstorms remain in the forecast this afternoon for the WA Cascades as the SPC has a general risk for thunderstorms across parts of the CWA. For tonight, conditions will trend drier area-wide as the aforementioned upper-low track southward and away. Overnight lows will bottom out into the lower to mid 50s.

The heat will intensify on Sunday and Monday. Upper-ridging will shift ever so gently over the region, allowing for more large- scale subsidence across the PNW. In concert, a surface thermal trough will build along the coast on Sunday as well, bringing a light spell of offshore flow. High temperatures will top out well into the upper 70s and 80s across the interior on both days. A marine push will usher in some natural AC by Monday evening as the coast and adjacent areas cool-down into the 60s.

The HeatRisk for the most part remains in the minor category Sunday and Monday due to the temperatures cooling off nicely in the overnight hours. Areas of moderate HeatRisk is in the forecast for inland portions of Grays Harbor county nearby locations primarily on Sunday.

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LONG TERM /TUESDAY THROUGH SATURDAY/

As mentioned, low-level onshore flow will increase on Monday night. Widespread marine stratus is expected into Tuesday as the cool-down ensues. Daytime highs are expected to be in the upper 60s to mid 70s. Coast remaining in the mid 60s.

Upper level ridge over the area weakening Wednesday, rebuilding Thursday then starts to move east Friday. Low level flow remaining light onshore. Relatively warm air aloft combined with only a shallow marine layer over the interior in the late night and morning hours will keep daytime highs above normal through the week. A little cooling Friday as the ridge starts to exit the area. Highs Wednesday and Thursday in the 60s to lower 70s, before settling into the 60s area wide on Friday. Lows in the 40s.

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AVIATION

Northerly flow aloft will develop this evening through Sunday as an upper ridge begins to develop offshore. VFR conditions this afternoon with a few high clouds and cumulus development over the Cascades. VFR conditions with mainly clear skies will continue through Sunday. N/NW surface winds this afternoon remaining breezy around Puget Sound with sustained winds ranging 7 to 12 kts and localized gusts to 20 kt. Winds will become lighter tonight, mainly from the N/NE.

KSEA... VFR conditions through the TAF period with high clouds at times. N/NW surface winds ranging 8 to 13 kts this afternoon with gusts to 20 kts. NE winds tonight from 7 to 10 kts. JD

MARINE

Thermally induced surface trough will build northward along the coast into Sunday with weak northerly, offshore flow developing. The thermal trough will shift into the interior on Monday allowing strong onshore flow to develop during the evening and resume increase toward the middle of next week. Westerlies in the central and east strait will likely approach strong SCA to gale force gusts Monday night into Tuesday morning.

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HYDROLOGY

No river flooding in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.