textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge will build across the Pacific Northwest early this week, resulting in warming temperatures through Tuesday. Temperatures will peak on Tuesday, resulting in Minor to Moderate HeatRisk as well as much lower daytime relative humidity values. Onshore flow increases Wednesday as the upper ridge weakens. The next disturbance approaches Western Washington later in the week.

SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/

Warm and dry weather on tap through Tuesday due to high pressure and offshore flow. Highs on Tuesday will reach the 80s to low 90s with warmest spots away from the sound. We're expecting minor to moderate HeatRisk for this event. The air mass will be dry as well with daytime min humidities in the 20s and 30s - keeping fire weather conditions elevated. However, gusty east winds will peak in the morning hours and not coincide with the warmest/driest conditions.

Wednesday brings cooler conditions with a trough and a return of onshore flow. Forecast highs are in the 60s to lower 70s and closer to average. The trough will bring a chance of showers and thunderstorms to the Cascades where instability is the greatest. Showers will taper down Wednesday night. 33

LONG TERM /THURSDAY THROUGH MONDAY/

A deep upper low, off BC, keeps western WA cool moving into the weekend. Highs will track a few degrees cooler than normal and in the lower to mid 60s. Expect lows in the 40s and 50s. Showers increase on Saturday as the low spins overhead. The air mass is slightly unstable for a chance of thunderstorms in the interior and Cascades. Showers with a convergence zone are expected too (over the north/central sound). A ridge brings some drying and slightly warmer conditions on Sunday. A weak, splitting front approaches the coast on Monday. 33

AVIATION

Northerly flow aloft tonight will become westerly on Tuesday as an upper ridge over the region gradually shifts eastward. Weak low level offshore flow will turn onshore late in the day on Tuesday. VFR conditions will prevail through Tuesday.

KSEA...VFR. Surface winds northerly 8 to 12 knots with occasional higher gusts this afternoon will ease this evening and become light northeasterly tonight. Winds will shift west/northwesterly Tuesday afternoon before backing southwesterly Tuesday night.

MARINE

Thermally induced low pressure will expand northward into the area tonight for light offshore flow. The thermal trough will shift inland Tuesday afternoon for the commencement of onshore flow. A dissipating frontal system will reach the waters on Wednesday. Surface high pressure will rebuild across the waters Wednesday night into Thursday for stronger westerlies in the strait. A broad trough and associated front will cross the waters Friday and Saturday.

Coastal seas are expected to remain below 10 feet through the period.

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FIRE WEATHER

An upper level ridge will setup a dry and warm pattern through Tuesday across the region with light offshore flow developing as a weak thermal trough builds north over the Puget Sound region. Tuesday remains on track to be the warmest day, with daytime high temperatures reaching into the 80s and a few spots touching 90. Winds still appear to be relatively light, but a few gusts to 15-20 mph near the Cascades and over the exposed ridgetops remain possible. Poor overnight recoveries are expected tonight into Tuesday morning, with daytime RHs Tuesday likely to approach 20%. However, this stretch appears short-lived, with a resumption of onshore flow bringing higher humidities for the second half of the week.

SEW WATCHES/WARNINGS/ADVISORIES

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