textproduct: Seattle/Tacoma

SYNOPSIS

A frontal system will move across Western Washington this morning, bringing continued rain and gusty 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/

Locally heavy rainfall and gusty winds remain the main weather impacts early this morning across portions of Western Washington. A fairly notable plume of moisture transported into the region along a frontal system continues to bring widespread rain to the coast and the northern portions of the area.

South winds are expected to be strongest over western Whatcom County, the San Juan Islands, and extending in the western Strait of Juan de Fuca eastward across Hood Canal to around Everett. Elsewhere, southerly winds will remain breezy through this morning. Rainfall amounts will be heaviest across the western slopes of the Olympic Peninsula, Skagit and Whatcom counties, as well as the Cascades from King County northward. Generally 1 to 3 inches of rain is expected for the mountains, with 0.50-1.25 inches in the lowlands of Skagit and Whatcom counties. With the stronger aloft, it's possible that some areas around central Puget Sound remain significantly shadowed from much of the precipitation. Winds will slowly subside through the day for most, though a westerly push through the Strait of Juan de Fuca late today may keep winds elevated in these areas.

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 aloft today and into Wednesday as a frontal system crosses then exits western Washington. Surface winds reflecting this strong flow aloft with heightened speeds for much of the TAF period. Majority of sites will experience south to southwesterly winds with speeds 10-15 kts. Gusts will enter the picture by 12-15Z this morning with speeds getting up to 30 kts at times. HQM and BLI are running a little hotter than this range with speeds more in the 15-20 kts range and the potential for mid to late morning gusts up to 35 kts. Overall, wind speeds will ease this evening as the front pulls away and as the direction shifts more north to northeasterly, falling back into typically 5-10 kts by 03Z with some locations going light and variable overnight tonight.

Wide variations in cigs this early morning with VFR, MVFR and IFR all being represented...category largely being associated with the presence of precipitation. Cigs will continue a downward trend for most terminals as the system continues to work its way through the area. Widespread MVFR to IFR conditions are expected to emerge in the 12-14Z time frame. While some terminals may improve to high-end MVFR to low-end VFR this evening and early tonight, lingering low- level moisture from this exiting front will likely present W WA with widespread MVFR to IFR conditions returning tonight and into Wednesday morning.

KSEA...MVFR ceilings starting to move over the terminal as of the 0926Z special ob and would expect this downward trend to persist throughout the morning. While a fair amount of shadowing seems to be occuring at the time of this writing, precip expected to reach the terminal in a 12-14Z window, which will hasten descent into low-end MVFR to high-end IFR conditions. Cigs recover somewhat this evening, perhaps even getting to 3000 ft early tonight...but enough low-level moisture expected to be present to keep this short-lived with MVFR to IFR conditions returning overnight and into Wednesday morning.

18

MARINE

A front will pass through area waters today. Winds easing over the coastal waters today, however seas remain high enough to keep inherited SCA in place there through this afternoon. Remaining headlines for interior waters with regards to wind look good and will remain in place with no adjustments. Onshore flow quickly diminishes 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.

27/18

SEW WATCHES/WARNINGS/ADVISORIES

WA...Wind Advisory until 2 PM PDT this afternoon for Lowlands of Western Whatcom County-San Juan County.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for Admiralty Inlet-Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-Puget Sound and Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning until 5 PM PDT this afternoon for Northern Inland Waters Including The San Juan Islands.