410 FXUS66 KPQR 100427 AFDPQR Area Forecast Discussion National Weather Service Portland OR 927 PM PDT Tue Oct 9 2018 Updated aviation discussion .SYNOPSIS...Cascade showers will decrease this evening. Patchy valley and coastal fog is possible late tonight into Wednesday morning. High pressure and offshore flow will result in dry weather Wednesday and Thursday. A weak system passing NE of the Cascades will briefly return onshore winds for Friday. High pressure returns this weekend with moderate offshore flow and warmer temperatures. Dry weather persists into early next week. && .SHORT TERM...Today through Friday...Showers are confined to the higher terrain this afternoon and will gradually decrease through the evening. Weak north flow will keep clouds around tonight especially over the higher terrain. There is a better chance for clearing for the interior valleys and along the coast, where lingering surface moisture and calm winds may lead to shallow fog or low clouds late tonight into Wednesday morning. An upper ridge builds Wednesday afternoon and a weak thermal surface trough sets up across NW Oregon. The thermal trough shifts towards the coast Wednesday night for more widespread offshore flow. The modeled east surface pressure gradient is around 3-4 mb Wed night which may produce enough wind and atmospheric mixing to limit radiation cooling and fog. A very positively tilted upper ridge sets up on Thursday. The thermal surface trough changes its shape, but continues to support offshore flow across the area. Clearer skies is on tap for Thursday with temperatures warming into the upper 60s to low 70s. An upper level shortwave trough slides NW to SE across Western Canada towards the Rockies Friday and dampens the upper ridge a tad. This feature will lower the surface pressure east of the Cascades disrupting the offshore flow. Light onshore winds are expected Friday afternoon and possibly an increase of coastal clouds. ~TJ .LONG TERM...Friday night through Tuesday...The 12z GFS and 12z ECWMF remain in good agreement. A massive upper level ridge will be the dominating feature. As the weekend approaches the ridge axis looks to tilt slightly positive. As a result a surface high over the Columbia River basin develops, and a surface low looks to develop in the Willamette Valley. This will cause a tightening of the surface pressure gradient along the Cascades, and will cause an offshore flow pattern develop. This tightening of the pressure gradient looks to lead to the most significant east winds so far this season. Gusts up to 35 to 45 mph near, and in the western Gorge are possible from Saturday through early Monday. Expect the the strongest winds to start on Saturday and continue through Sunday evening. During this time period the entire area will stay dry, along with temperatures around seasonal to slightly warmer than seasonal. Highs in the upper 60s to mid 70s, and lows in the mid to upper 40s in the upper Willamette Valley. Along the Cascades and portions of the southern Willamette Valley could see low temperatures in the lower to mid 30s. This overall pattern is expected through Tuesday. /42 && .AVIATION...Mainly VFR the next 24 hours at most sites, but could see some patchy or shallow ground fog develop along the coast tonight and in sheltered locations in the interior Wednesday morning. There is still a question about how strong the offshore flow will be tonight if it develops which could prevent any fog or low stratus development. Will need to monitor this as the night goes on to see if any fog or low stratus develops tonight and bring IFR or LIFR conditions or if conditions remain VFR. Expect any reduced flight conditions that does develop tonight to improve to VFR by late Wednesday morning. KPDX AND APPROACHES...Mainly VFR the next 24 hours with light east winds developing late tonight. This will likely prevent fog or low stratus from developing, but if the wind are weak we could see a few hours of IFR conditions Wednesday morning. /64 && .MARINE...Winds are already starting to ease this afternoon behind the effects of a weak cold front which moved through the waters earlier today. Seas remain above 10 ft and very choppy, but will begin to subside this evening. Could see some square seas at 9 ft even after seas drop below 10 ft tonight, so Small Craft Advisory for Hazardous Seas may need to be extended, but will keep the timing as is for now while keeping an eye on trends. High pressure will build over the waters starting Wednesday afternoon, bringing the return of a summer-like northerly wind pattern for a few days. Seas will also subside during the period, falling to around 4 to 6 ft by the time the weekend rolls along. Bowen && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory for hazardous seas until midnight PDT tonight for Coastal Waters from Cape Shoalwater WA to Florence OR out 60 NM. Small Craft Advisory for Rough Columbia River Bar until 9 PM PDT this evening. Small Craft Advisory for Rough Columbia River Bar from 4 AM to 7 AM PDT Wednesday. && $$ 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 CWA or forecast area.