000 FXUS66 KSEW 050333 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 833 PM PDT Sat Apr 4 2020 .UPDATE...Dry conditions across most of Western Washington this evening with light offshore flow. Light rain is sliding northward across portions of southern WA with an upper level low offshore, however not much in the way of precipitation is expected with dry air over the area. Slight chance of a showers across the Southwest Interior and South Sound into tonight. Dry conditions for Sunday. Winds light northerly. && .SYNOPSIS...Upper level low offshore will move south tonight and Sunday. A weak upper level trough will move over the area from the north Sunday. Upper level ridge to build offshore Monday with the ridging moving inland in the middle of next week. Another weather system will try to move through the ridge next Friday or Saturday. && .SHORT TERM /TONIGHT THROUGH TUESDAY/...Satellite imagery shows mostly cloudy skies over most of Western Washington this afternoon. Doppler radar not picking up any shower activity at 23z/4 pm with the leading edge of the band of showers moving up from the south near Portland. Temperatures were in the mid 40s to lower 50s. Upper level low well offshore will continue to dig south tonight. This will make the flow aloft over Western Washington more southernly pushing the shower activity over the Portland area north into the Southwest Interior. This feature is splitting slightly as it moves north so expect the shower activity to die off before it reaches the Central Puget Sound. Mostly cloudy conditions will continue overnight. Lows in the 30s and lower 40s. Upper level low offshore continuing to move south Sunday with the southerly flow aloft shutting off then being replaced by a drier northwesterly flow aloft as an upper level trough moves into the area. Air mass slightly unstable with the trough but with the limited moisture will confine the chance of showers mostly to the higher terrain. Some mid and high level moisture will keep skies partly sunny/mostly cloudy. Highs a little warmer, in the lower to mid 50s. Upper level trough hanging over the area Sunday evening before kicking off to the east early Monday morning. This will keep the threat of showers in the Cascades intact Sunday night. For the remainder of the area cloud cover decreasing overnight as the trough moves east. Lows Monday morning in the 30s with the cooler locations near freezing. Northwesterly flow aloft continuing on Monday as an upper level ridge slowly starts to build over the eastern Pacific. Low level onshore flow will bring some morning clouds to the area with mostly sunny skies in the afternoon. Highs in the 50s with lower 60s possible over the Southwest Interior. Upper level ridge continuing to slowly build offshore Monday night into Tuesday with dry northwesterly flow aloft. Surface flow remaining onshore combined with the ridge being relatively weak will keep high temperatures mostly in the 50s but Tuesday will be a dry day. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...Extended models in good agreement Wednesday and Thursday with the upper level ridge nosing into the area Wednesday night and Thursday. Thursday looks to be the warmer day of the two sunny days with warmer locations getting into the mid 60s. The forecast high of 63 on Thursday would be the warmest day in Seattle since October 24th. Most of the high Wednesday and Thursday will be in the 50s and lower 60s. Model consistency breaks down Friday and Saturday with the ECMWF keeping the ridge in place Friday followed by a very weak system Saturday. The GFS breaks the ridge down sooner with rain spreading into the area Friday with a trough trailing the system for Saturday. ECMWF ensemble solutions for Friday have about 20 percent of the members indicating light precipitation, a little more wet then the operational solution. The GFS has a little over half the ensemble members indicating precipitation, drier than the operational run would indicate. End result will have chance pops in the forecast Friday. A few more of the ensemble members are wet for Saturday in the ECMWF but the precipitation is light. Given the inconsistency in the models will stay with chance pops for Saturday. Felton && .AVIATION...Southerly flow aloft with an upper level low offshore tonight. Mainly dry conditions expected with light rain chances mainly along the WA/OR border tonight. VFR cigs into Sunday. Northerly winds 5 to 10 knots. KSEA...VFR cigs. North winds to 10 knots tonight. JD && .MARINE...An area of low pressure will slide south offshore of OR/CA into Sunday. Northerly flow across Western Washington. The flow will turn onshore on Monday as high pressure builds over the NE Pacific. Small Craft Advisory, or possibly gale winds, through the Strait of Juan de Fuca Monday evening. Light onshore flow Tuesday and Wednesday across the area. JD && .HYDROLOGY...River flooding not expected in the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$ www.weather.gov/seattle
NWS SEW Office Area Forecast Discussion
Discussion Script by Ken True at Saratoga Weather - WFO Script by SE Lincoln Weather
