Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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645 FXUS66 KSEW 232240 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 340 PM PDT Tue Apr 23 2019 .SYNOPSIS...Onshore flow and a Convergence Zone will give a chance of showers to the Cascades and central Puget Sound area this evening. A weak ridge of high pressure will give partly sunny and dry conditions on Wednesday. Clouds will increase on Thursday as onshore flow develops, but conditions will remain dry. A weak trough and low level onshore flow will give a chance of showers, mainly to the mountains and northern portions of the interior Friday into early next week. && .SHORT TERM /TONIGHT THROUGH FRIDAY/...Radar and satellite imagery show onshore flow producing a convergence zone from the Cascades of Snohomish and Skagit counties westward across Everett, the northern Kitsap Peninsula and the Port Townsend area. This area of convergence will likely stay about where it is this evening then slowly dissipate overnight. A chance of showers continues for these areas through the evening hours. A broad and progressive upper ridge will give low level northerly flow to the area as well as drying on Wednesday. Highs will be mainly in the upper 50s to mid 60s. A broad and weak upper trough will approach the area from the west on Thursday. A rather thick layer of moisture in the mid and upper levels will bring increasing clouds to the area through the day, then some lower clouds will spread inland during the evening hours as low level flow becomes onshore ahead of the incoming trough. Despite the cloud cover, expect highs to be in the 60s. Despite the increase in moisture aloft, expect it to remain dry. The broad trough with increasing flow aloft will give partly to mostly cloudy skies to the region on Friday along with an increase in onshore flow and a chance to slight chance of showers (mainly to the Cascades and northern portions of the area). Onshore flow will result in daytime temperatures falling a few degrees, back to around the 60 degree mark. Albrecht .LONG TERM /SATURDAY THROUGH TUESDAY/...Troughing will dominate conditions over the weekend. Models continue to show mainly only chance pops with partly to mostly cloudy conditions across the region. Snow levels will be low, as low as 3000 ft or so at times, so some snow showers may be seen in even the lower passes. Precipitation amounts appear that they will be rather light, so no significant impacts are expected at this time. Models generally agree that the early week period will be dominated by a weak trough that will provide partly to mostly cloudy conditions with a chance of showers and temperatures near normal for late April. While models do show a good deal of consistency today, their continuity with previous solutions is not good. Forecasts represent a blend of the ECMWF with the National Blend of Models. Albrecht && .AVIATION...A weak ridge will build over western Washington on Wednesday. Satellite imagery has indicated clouds breaking up over portions of the region this afternoon, with current conditions ranging from VFR to MVFR across the board. Guidance suggests that ceilings could become MVFR tonight, but it does seem likely there will be more clearing on Wednesday. Westerly winds aloft will become northwesterly during the overnight hours. Surface winds for terminals along sound are southerly in the 10-15kt range with a few gusts near 20kts. Winds then turn to the E/NE for terminals near the south sound tonight. KSEA...VFR cigs this afternoon. Cigs could drop back down to MVFR during the overnight hours, however are expected to lift back to VFR early Wednesday. Southwesterly winds 10-15 knots, becoming more east- northeasterly tonight. Borth && .MARINE...Onshore flow will persist across the coastal waters tonight and will continue to bring a strong push of westerly flow down the Strait of Juan de Fuca. Recent observations have already indicated gale strength westerlies in the central Strait this afternoon, while winds have recently started to pick up in the eastern Strait. SCA strength winds will likely bleed in to nearby Admiralty Inlet and Northern Inland Waters. Have also issued a SCA for Puget Sound this afternoon, as observations have indicated gusty southwesterlies in the southern portion of the Sound. Northwesterly SCA strength winds will remain possible for waters in the northern Sound. Winds will die down in the Strait early on Wednesday, however northerly SCA strength winds will continue into the morning hours for the coastal waters. Borth && .HYDROLOGY...The daily hydrology discussion has ended until the start of the next rainy season; it will be updated as needed until then. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 8 PM this evening to 8 AM PDT Wednesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Small Craft Advisory from 8 PM this evening to 5 AM PDT Wednesday for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Gale Warning until 3 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 3 AM PDT Wednesday for Northern Inland Waters Including The San Juan Islands. Small Craft Advisory until 5 AM PDT Wednesday for Admiralty Inlet. Small Craft Advisory from 8 PM this evening to 2 AM PDT Wednesday for Puget Sound and Hood Canal. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.