Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 182234 AFDPQR Area Forecast Discussion National Weather Service Portland OR 230 PM PST Sun Nov 18 2018 .SYNOPSIS...Dry weather with mild days and cool nights will continue through Tuesday as high pressure east of the Cascades brings offshore flow. A return to a wet pattern will begin Wednesday as frontal systems move into the region from the Pacific. This pattern will bring valley rain and mountain snow to the area through the end of the week. Snow levels will be down to pass levels in the Cascades Thursday though Saturday. && .SHORT TERM...Tonight through Wednesday...A dry offshore flow will continue through Tuesday as a strong ridge of high pressure slowly moves across the region. Persistent surface high pressure over the Columbia basin will maintain a fairly strong offshore flow, with PDX-DLS pressure gradient on the order of -7 to -8 mb, which is a bit weaker than the gradients we had with the east wind event this past week. The continental dry air will tend to limit fog potential the next few nights and mornings despite clear skies and light winds away from the gorge. The easterly flow through the Gorge is expected to cause some stratus redevelop in the central Gorge and up into the Hood River Valley. Models continue to show the upper ridge moving east Tue night and Wed as an upper trough slowly approaches the coast. Models have tended to slow the approach of the trough and surfae frontal system from previou runs, which is typical for the initial system pushing into an upper ridge. Time height moisture profiles with the initial system Tue night through Wed night are less than impressive, with predominantly mid and upper level moisture. Will hold off pops until Wed morning given the slowing, and limit categorical pops to coast and mountains, with likely pops in the inland valleys. With the cool nighttime temps around Hood River expected to continue and the threat of rain moving in Wed morning, will need to retain a chance for some freezing rain then. .LONG TERM...Wednesday night through Sunday...Models in a bit better agreement with the system moving in Thursday than they were this time yesterday. A more vigorous front expected to push inland late Thu with deeper moisture, so expect a decent shot of rain as the front moves in, followed by showers in a cool onshore flow through Fri. Snow levels some down with the front Thu, lowering to Cascade passes, with accumulating snows to follow. There remains a possibility for strong winds along the coast with both the 12Z GFS and EC solutions, although placement of the surface low continues to vary with each model run. Beyond Fri, models continue to diverge significantly in solutions, with EC favoring ridging and drying, while GFS is initially wetter and slower to develop an upper ridge. Will tend to back off some more on pops through the weekend, but will retain low pops through Sun given model uncertainties and relatively high climatological pops. && .AVIATION...VFR conditions continue across the region under clear skies today with high pressure over the region. Meanwhile, breezy east winds continue through the western gorge and extending out to KTTD, but likely will not extend to any of the other Portland metro area terminals today. Expect that low MVFR stratus will return to portions of the central gorge and areas around K4S2 overnight. It is possible that some shallow fog develops late in the south valley around KEUG as wind eases and radiational cooling becomes more efficient, but not enough confidence in restrictions developing to include in TAF at this time. PDX AND APPROACHES...VFR conditions through the period under clear skies. Gusty east winds east of the terminal near KTTD, but winds will be lighter at the terminal and may vary between east and northwest at times. Cullen && .MARINE...Weather conditions across the waters remain fairly benign through the first half of this week as large-scale high pressure remains over the coastal waters. This pattern will shift more dramatically around midweek as a much more active pattern begins to emerge. Expects high-end advisory strength gusts when the first system arrives late Tuesday into Wednesday. Meanwhile, seas will approach 10 feet with this front. A stronger system arrives around Thursday, with the potential for solid gales and seas well into the 15-20 ft range late Thursday through early Friday. Will need to continue to evaluate model trends to see if storm force gusts may even be possible with this second system. The more active pattern looks to continue into next weekend, but forecast models diverge rather quickly so confidence in details for this time becomes much lower. Cullen && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland 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 forecast area.

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