Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 190411 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 900 PM PDT Mon Sep 18 2017 .SYNOPSIS...An upper trough over the area through Wednesday will bring cool and showery weather. Drier northerly flow aloft will develop late in the week as an upper ridge moves toward the area. && .SHORT TERM...An upper trough over the Pacific Northwest tonight and Tuesday will give cool weather and showers at times. An upper short wave will move through the area tonight, enhancing showers, especially to the south. There could also be isolated thunderstorms this evening, mainly near the coast. There was a severe-looking thunderstorm in far southwest Washington around 5 PM this afternoon, and a warning was issued for Lewis County, but the storm faded before reaching Lewis County and the warning was allowed to expire. Another short wave will push onshore Tuesday night. It looks like the heavier shower activity will be south of the area. The upper trough axis will shift inland Wednesday and Thursday with drier northerly flow aloft developing and a decreasing shower threat. Highs the next few days will be several degrees below normal. Snow levels will be around 5500 feet the new few days and the highest elevations could get some snow accumulations. There has been rain at Paradise but no snow accumulation, at least according to the avalanche sensor. There will probably be some light accumulations tonight and again Tuesday night as short waves bring increased showers - but temperatures look just a little too warm for snow to really pile up. Schneider/Burke .LONG TERM...Previous discussion...An upper ridge over the northeast Pacific will give dry northerly flow to Western Washington Friday through Monday. Highs will warm back to near normal. Schneider && .AVIATION...Upper level trough over the area with northwesterly flow aloft. Air mass moist and unstable with onshore flow. Multiple cloud layers over Western Washington between 4000 and 10000 feet with ceilings lowering down to near 2000 feet in showers through early Tuesday morning. Ceilings around 2000 feet becoming more widespread after 09z with the 2000 foot ceilings over most of the area by 13z. Ceilings near 2000 feet continuing through Tuesday morning with some improvement Tuesday afternoon. KSEA...Ceilings 4000-6000 feet lowering to near 2000 feet in the 09z-12z time frame. Ceilings remaining near 2000 feet through Tuesday morning with some improvement Tuesday afternoon. Southerly winds 5 to 10 knots through Tuesday morning. Felton && .MARINE...Low pressure will remain over the region through midweek. A trough will move through the area overnight with another trough reaching the area late Tuesday night and Wednesday morning. Strongest winds with this trough will be south of the area. Small craft advisory winds along the Coast tonight will ease on Tuesday. Winds over the remainder of the area forecasted to be 20 knots or less through Tuesday. Winds will becoming light northerly on Wednesday as low pressure passes to the south. Swell along the Coast will increase to over 10 feet overnight and remain above 10 feet into Tuesday afternoon. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 11 AM PDT Tuesday 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 for hazardous seas from 11 AM to 5 PM PDT Tuesday 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 for rough bar from 4 AM to 8 PM PDT Tuesday for Grays Harbor Bar. Small Craft Advisory until 1 AM PDT Tuesday 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. Small Craft Advisory for hazardous seas from 1 AM to 5 PM PDT Tuesday 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-West Entrance U.S. Waters Strait Of Juan De Fuca. && $$ www.weather.gov/seattle You can see an illustrated version of this discussion at www.wrh.noaa.gov/sew/gafd/latest_webafd.html

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