000 FXUS66 KSEW 191714 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 930 AM PST Mon Nov 19 2018 .SYNOPSIS...High pressure aloft will maintain cool dry weather through Tuesday. Patchy night and morning fog or freezing fog will give way to afternoon sunshine with highs reaching into the low to mid 50s. A series of low pressure systems will bring wet weather beginning Wednesday and continuing through the weekend. && .SHORT TERM...A ridge of high pressure will maintain dry conditions through Tuesday. Areas of fog or freezing fog is likely again later tonight and Tuesday morning. Highs will reach the low to mid 50s today and Tuesday, with lows Tuesday again dipping into the 30s with sub-freezing temperatures in colder valleys. High clouds will start to increase Tuesday as high pressure shifts inland ahead of a split trough approaching the region. Models will no doubt have difficulty handling this split flow pattern as the two streams battle for dominance. Most the energy typically splits off with the southern portion, which models show tracking into Oregon and CA. The northern stream will be still be active, but the potential for heavy precipitation will be less in this pattern. Rain with the first split front will reach the coast early Wednesday morning and quickly spread inland. QPF in the mountains looks to around a few tenths with less much less in the lowlands. Cooler air arrives with the front and snow levels should steadily drop to around 3500 to 4000 feet Wednesday night into Thanksgiving. A few inches of snow could fall at higher passes Wednesday night and Thursday. Higher passes like Stevens and While pass are most likely to see these amounts, while Snoqualmie pass may only see a couple inches. Motorists planning travel through Cascade passes should pay close attention to the forecast through the holiday weekend as the an active weather pattern is anticipated. Mercer .LONG TERM...Previous discussion...Models have been consistent in showing another, wetter system arriving Thursday, followed by an upper trough for showers Friday. High temperatures will fall to around 50 on Thursday and into the upper 40s on Friday. The snow level will fall to around 3000 feet on Friday. During the wettest period, about 18Z Thursday to 18Z Friday, several inches of snow are likely in the passes--possibly even advisory amounts. Models diverge somewhat after Friday. The GFS brings another system into the region Saturday, while the latest Euro run builds a ridge and is pretty dry both Saturday and Sunday. For now have disregarded that solution and kept likely pops Saturday with chance pops Sunday. Highs both days will be 45-50, with lows around 40--pretty close to average for this time of year. Burke && .AVIATION...A strong upper ridge over the region will continue through Tuesday, then shift east. Light southerly flow will become moderate Tuesday. The air mass remains dry and stable except for near surface moisture, trapped by the subsidence inversion. Areas of fog or freezing fog this morning will develop again later tonight and Tuesday morning. Fog should dissipate by midday today and again Tuesday. Local IFR fog is likely again tonight/Tuesday morning. KSEA...Patchy IFR fog in the vicinity of KSEA should dissipate by midday, with VFR prevailing this afternoon and evening. Surface winds light and variable becoming northerly 5 to 10 knots in the afternoon. DTM && .MARINE... High pressure will remain in control with mainly easterly flow through Tuesday. A series of low pressure systems will move across the area from late Tuesday night through the end of the week. Stronger onshore flow is likely with periods of small craft advisory conditions from time to time. It`s possible there could be a period of gales over the coastal waters Thursday into Friday with second stronger system but will have to monitor the forecast going forward. CEO && .HYDROLOGY...A pattern change will get underway late Tuesday with a series of low pressure systems moving across the area Wednesday into the end of the week. Snow levels will be lowering with these systems, down to around 3000 feet by Friday. At this time, rainfall amounts do not look high enough to cause any river flooding but river levels will be on the rise. Still some uncertainty with the model precipitation forecasts so will continue to monitor. CEO && .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
