textproduct: Seattle/Tacoma

SYNOPSIS

The upper level low currently bringing rain to the region will depart tonight. Cool and cloudy conditions persist into Monday, then an shortwave trough will bring chances for showers, mainly in the mountains, early Tuesday. Dry and warmer conditions are expected mid-week onward as upper level ridging builds.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/

A surface low pressure system, supported by an upper level low directly overhead, will continue to move through and move east of Washington tonight. Rain continues to fall across areas of Seattle and southward, and east the coastline. Rain will taper off across the interior. The bulk of the rain will end over the mountains tonight, through chances for scattered light showers from stronger onshore flow will continue through the overnight period tonight. Winds will also increase this evening, with peak gusts of around 20-30 mph across portions of the Puget Sound lowlands, the northern interior, and the Strait of Juan de Fuca through early Monday morning. A few breaks in the clouds may be possible this evening before convergence zone and marine layer clouds fill in tonight into Monday morning. Monday will see a slow break up of the clouds through Monday evening with mostly dry conditions. Highs today and Monday in the mid to upper 60s, with lows in the upper 40s to mid 50s.

Following the departure of the upper level low on Monday, dry northwesterly flow will persist on Monday, through this will drag a shortwave trough down along the British Columbia coast and move across western Washington early on Tuesday. Most locations will just see an increase in clouds again Tuesday morning, though there will be slight chances for some isolated showers, mainly in the mountains, on Tuesday morning. Clouds will begin to clear late Tuesday. Temperatures will remain mild, with highs in the mid 60s to near 70. Lows in the mid 40s to low 50s.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

The trough will continue to sink southward on Wednesday and still over the OR/CA border, with upper level ridging nosing over western Washington. This should be enough to develop a weak surface thermal trough along the coast, allowing the low level flow to turn offshore. This will help to promote warmer and dry conditions through the end of the week. Highs, beginning Wednesday, will rise into the mid 70s to low 80s in the warmest locations. This should last through the at least the end of the week. Models are hinting that the pattern should progress next weekend, but is uncertainty as to how quickly the low to the south will exit and allow the ridge to progress east as well.

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AVIATION

Northerly flow aloft will become more northwesterly into Monday as an upper level low departs the area. Outside of a few light showers across the Cascades, rain has largely tapered across western WA this evening. Conditions at the area terminals are primarily a mix of MVFR and VFR. Expect more widespread MVFR to IFR conditions to return to the area terminals overnight into Monday. Widespread VFR conditions look to return around 21Z as clouds slowly lift. Gusty winds to 20-25 kt expected in the interior through 12Z with increasing onshore flow tonight. Winds will ease Monday and will primarily persist out of the SW/W between 5-10 kt.

KSEA...Primarily MVFR conditions at the terminal this evening in low clouds. MVFR conditions will continue into Monday, with improvement towards VFR expected around 21Z. Gusty S/SW winds to 20-25 kt expected through 09Z, with winds easing and primarily persisting out of the SW at 5-10 kt on Monday. 14

MARINE

Increasing onshore flow tonight with Small Craft Advisory winds over Puget Sound/Hood Canal, Northern Inland Waters and the Strait of Juan de Fuca. Winds will ease early Monday morning. Weak onshore flow on Monday with the flow turning more northerly on Tuesday. Offshore flow will develop Wednesday and Thursday as a thermal trough forms along the coast. Onshore flow will return Friday and into the weekend. 33

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 5 AM PDT Monday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.