Area Forecast Discussion National Weather Service Portland OR 923 PM PST Thu Dec 14 2017 .SYNOPSIS...A front approaches the region tonight and spreads light rain across the area Friday. A series of fronts will move into the region after Friday with lowland rain and mountain snow at times through at least the first half of next week. && .SHORT TERM...Tonight through Sunday...Satellite imagery this evening shows most of Western Oregon in a break from high coverage of cirrus, which has allowed temperatures to drop below freezing at sites in the southern Willamette Valley and outlying inland areas. Adjusted overnight minimum temperatures to account for this cooling. Also moved precipitation chances inland to 15Z Friday as most models are showing a little bit of a later arrival. This should give enough time for a few degrees of morning warming such that freezing precipitation shouldn`t be an issue. However, if some very light rain or drizzle arrives in the valley before 15Z, could see some patches of it freezing. Woudldn`t expect any significant or widespread impacts even in that case, with warming following shortly as winds switch onshore with the front. Bowen Rain will transition to showers later Friday evening, with diminishing shower coverage overnight. Snow levels will fall behind the front with accumulating snow down to around 2,500 feet on Saturday. However, snow amounts should be rather modest with less than an inch in the upper foothills and lower Cascades, and 1-3 inches at pass elevation. Snow levels will then rise above the Cascade passes late Saturday night as a warm front moves through the region. This will bring another round of rain on Sunday and have maintained chance PoPs across this area with highest chances over southwestern Washington. However, would not be surprised if areas south of a Newport to Salem line remain dry over the weekend. Cullen .LONG TERM...No Changes. Previous discussion follows...Sunday night through Thursday...Models are in decent agreement the area will be under zonal flow with the jet stream remaining across southern British Columbia and far northern Washington Sunday night and Monday. This will leave our more northern zones open to a period or two of light rain as a weak front drags southward towards the region, but rain chances appear considerably less towards Lane County. Models seem to also be coming into agreement a shortwave trough and attendant front will drop southeastward out of the Gulf of Alaska and usher in a good shot of valley rain and mountain snow Tuesday and Tuesday night. As upper level ridging builds northward into British Columbia behind this feature late Wednesday and Thursday, our flow should become increasingly northeasterly. This will in turn likely lower snow levels to near the valley bottom, but precipitation will almost certainly have ended by that point. If precipitation were to linger across the area Wednesday night and Thursday, our flow will likely not be quite as northeasterly, and as a result, snow levels will likely be higher. /Neuman && .AVIATION...VFR with light to moderate offshore flow this evening, except for some low clouds causing MVFR and mountain obscurations around the Hood River Valley. Offshore flow is lighter in general tonight, and may allow a little more fog to develop in the south Willamette Valley overnight. Otherwise, expect VFR and high clouds to persist until cloud bases start to lower with the approach of a cold front Fri morning. Will add roughly 4-6 hours of -RA and MVFR to all TAFs Friday; starting in KAST around 14z then spreading south and east with the front as the day progresses. This front will finally bring an end to the strong E winds through the Columbia Gorge Fri morning, as our general flow pattern turns more onshore. PDX AND APPROACHES...VFR with decreasing E-SE winds through 12z Fri. Cold front will bring lowering cigs Fri morning, with -RA and MVFR likely by 18z Fri. Rain will taper to showers behind the front Fri afternoon. Weagle && .MARINE...Light SE winds will shift to a N-NW wind later tonight/early Fri as a weak cold front moves across the waters. The SCA for winds in the outer waters Friday looks marginal, but most models do show 25 kt winds in the boundary layer, which indicates some gusts may reach that high. Decided to shorten the tail end of the advisory a bit, as high pressure should cause winds to ease Fri evening. Seas will likely remain just below 10 feet for the most part with this system, though shorter periods may make it a bit rough late Fri night/Sat. Latest ENP guidance shows lighter seas in between fronts later Sat through early Sun, then another weak frontal system is expected later Sunday. Swell energy from the Gulf of Alaska will again push seas close to 10 ft behind this front Sun/Mon. A stronger cold front may bring low-end gales Tue, with seas potentially pushing into the teens.Weagle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory until 10 AM PST Friday for Central Willamette Valley-South Willamette Valley. WA...None. PZ...Small Craft Advisory for winds from 7 AM to 8 PM PST Friday for Waters from Cape Shoalwater WA to Florence OR from 10 to 60 NM. && $$ This discussion is for Northwest Oregon and Southwest Washington from the Cascade crest to 60 nautical miles offshore. This area is commonly referred to as the CWA, or forecast area.