textproduct: Seattle/Tacoma

SYNOPSIS

A frontal system will move across Western Washington this morning, bringing continued rain and breezy winds. High pressure builds aloft over the Pacific Northwest Thursday and Friday, with just a slight chance of precipitation. The upper ridge further builds next weekend for drier, warmer conditions.

SHORT TERM /TODAY THROUGH THURSDAY/

A frontal system continues to move across western Washington this morning. Rain will slide southwards through this afternoon, with the heaviest rainfall amounts remaining in the north and central Cascades. South winds remaining breezy, mainly across Puget Sound into this afternoon. The Wind Advisory has been cancelled for the San Juan Islands and western Whatcom County as winds slowly ease in these areas in the next couple hours. A westerly push through the Strait of Juan de Fuca late today may keep winds elevated in these areas. Winds subside elsewhere late today and tonight.

An upper ridge slowly begins to build over the Pacific Northwest on Wednesday, resulting in drier conditions. Areas of stratus and morning fog may occur Wednesday AM due with lingering low- level moisture and light winds under the building high pressure. Temperatures residual moisture at the surface. Temperatures will be cooler than normal but gradually warmer Wednesday and especially Thursday reaching back in the mid to upper 60s.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

Ensemble guidance remains in fairly strong agreement that the flow aloft becomes more zonal by Friday. This will at least open the door for some light precipitation across the region, though the likelihood is somewhat low for much in the way of significant precipitation. After this, the pattern would likely favor a return of high pressure and some light offshore flow. This could yield a somewhat mild start to October, with temperatures into the lower 70s. Some uncertainty in the ensembles in regards to the return of more onshore flow early next week, but overall, warmer and drier conditions are expected during this period.

AVIATION

Strong westerly flow will persist aloft today and into Wednesday as a frontal system moves across western Washington. Surface winds reflect this strong flow aloft with heightened speeds expected through this afternoon. The majority of the sites will experience south to southwesterly winds with speeds 10-15 kts with gusts between 25-30 kt at times. Winds at HQM are a bit stronger, with speeds between 15-20 kts and gusts 30-35 kts at times. Overall, wind speeds will ease by this evening as the front pulls away from the area and the wind direction shifts to the north to northeast. Expect winds to subside to 5-10 kts by 03Z with some locations going light and variable overnight tonight.

There remains a wide variation in cigs across the terminals this morning, though conditions are predominantly MVFR to IFR. Cigs will continue to trend downward in rain as this frontal system works its way through the area. While some terminals may improve to high-end MVFR to low-end VFR this evening into early tonight, lingering low-level moisture from this exiting front will likely bring another round of widespread MVFR to IFR conditions to the terminals overnight into Wednesday morning.

KSEA...MVFR ceilings at the terminal this morning. While a fair amount of rain shadowing is occuring, precip still looks to fill into the terminal between 18-21Z. Brief reductions to IFR cigs remain possible as the rain moves in. Cigs will then recover back to around 3000 ft by early tonight...but expect improvement to be short-lived as low-level moisture will likely bring the return of MVFR to IFR conditions overnight into Wednesday morning. Southwesterly winds between 10-15 kt with gusts to 25 kt will ease towards 5-10 kt this afternoon and switch to the north/northeast around 00Z.

18/14

MARINE

Breezy winds will continue across the area waters today as a front pushes through the region. Winds have, however, started to ease across the Northern Inland Waters in the front's wake, so have transitioned the Gale Warning over to a Small Craft Advisory this morning. Seas across the coastal waters remain high enough to keep inherited SCA in place there through this afternoon. Elsewhere, expect small craft strength winds to continue through this afternoon.

Onshore flow will diminish by early Wednesday. As such, seas also diminish quickly as the system gets further away from the coastal waters with wave heights around 7 ft by this evening and down further to 4-6 ft by midday Wednesday. Surface high pressure building over the interior of British Columbia and weak troughing just offshore will lead to some weak east/southeast flow on Thursday. Thermally induced surface low pressure begins to expand northward along the coast toward the weekend for northerly or weak offshore flow across area waters.

18/14