Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 241111 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 330 AM PDT Sat Mar 24 2018 .SYNOPSIS...Rain and snow showers will decrease this afternoon. A few showers will linger tonight into Sunday but most the area will be dry. Weak fronts brushing the area will bring light rain at times Sunday night through at least Tuesday. Showers should taper off on Wednesday as high pressure builds over the region through the end of the week. && .SHORT TERM...IR/WV satellite imagery shows a well defined short wave lifting northeast across the area early this morning. The main 1006 mb surface low feature has now moved into southeast WA but the upper level low is negative tilt with showers lifting north into Wrn Washington. A weaker 1010 mb low near the WA coast is also providing some added lift and instability. Models generally agree that rain or showers will be widespread over interior Wrn WA from around Puget Sound to the south and east. Radar appears to shows this playing out with the bulk of steadier rain along the I-5 corridor north to around Arlington. The main concern is whether rainfall rates will support an isothermal profile that drive snow levels down toward the surface. The Sandpoint profiler shows cooling the past few hours but dew points and temperatures are still in the mid/upper 30s at most locations. There are a few spots with wet snow reported over Pierce county inland from the water like Puyallup. However, with the main precipitation band shifting eastward the next couple hours, most spots will probably not get more than a dusting. A snow advisory was issued last evening for the east Puget Sound lowlands for up to 2 inches and the Cascades of Pierce/Lewis counties for up to 6 inches at Paradise. Both advisories look marginal but will leave them in place for now and watch radar trends. With rain now transitioning to snow in the foothills, a wet inch or two of accumulation is still possible. Showers will decrease this afternoon with just a few lingering showers through Sunday. Weak low pressure will remain over the region but Western Washington will be in drier period between fronts. Both the ECMWF and GFS bring the next front into the area Sunday night or Monday with a return to light rain at times. .LONG TERM...A moist northwest flow pattern will maintain cool temperatures with rain at times through at least Tuesday. The GFS and ECWMF differ on the strength of the ridge expected to build around the middle of next week. Little change was made to the forecast which is closer to the ECMWF idea of a stronger ridge Wednesday through the end of the week. Lingering showers should dissipate Wednesday with a period of mostly dry weather expected Thursday and possibly Friday. Highs should reach back into the 50s. Mercer && .AVIATION...Upper level low off northern Oregon coast continuing to move south today. Southwesterly flow aloft becoming light and variable this afternoon. Air mass moist and somewhat unstable. Last organized band of showers moving through the area early this morning with ceilings in the interior from about KPAE southward in the low end of MVFR or IFR. For the remainder of the area ceilings near 5000 feet. Improving trend later this morning into the afternoon hours with ceilings aoa 5000 feet all areas by 00z. Improving trend continuing into the overnight hours. KSEA...Ceilings below 1000 feet slowly improving around 16-18z to the 1000-2000 foot range. Improving trend accelerating in the afternoon hours with ceilings aoa 5000 feet by 00z. Variable wind early this morning becoming southerly 4 to 8 knots mid morning. Winds trying to come around to northwesterly late in the afternoon but ending up in the 230-260 degree range. Felton && .MARINE...Low pressure offshore will shift south and weaken today. Weak high pressure will move over the area later today and tonight. A couple of weak fronts cross the area Sunday and Monday. Moderate onshore flow will develop Tuesday and continue into Wednesday. Schneider && .HYDROLOGY...River flooding is not expected the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Winter Weather Advisory until 10 AM PDT this morning for East Puget Sound Lowlands. Winter Weather Advisory until 11 AM PDT this morning for Cascades of Pierce and Lewis Counties. PZ...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.