Area Forecast Discussion National Weather Service Portland OR 236 PM PDT Sun Aug 20 2017 Corrected typo in aviation section .SYNOPSIS...Onshore flow will produce varying degrees of morning clouds, afternoon sunshine. with inland temperatures in the 70s and 80s for much of the next week. Monday and Tuesday will likely be the warmest days as a flat upper ridge moves through. A weak system will bring significant cooling to the forecast area late Wednesday and Thursday, as well as more clouds and a few light showers to the forecast area Wednesday night and Thursday. Expect drying as temperatures warm back to above seasonal normals levels next weekend. && .SHORT TERM...Tonight through Wednesday...Other than some passing higher clouds from a weak system passing by to our north, skies were sunny over most of southwest Washington and northwest Oregon this afternoon. Low clouds are consolidating along the south Washington and north Oregon coasts this afternoon, largely due to the system passing by to our north. Temperatures today are still on track to be near or just above seasonal normals, with 80 to 85 common inland from Vancouver southward. As mentioned above, low clouds are solidifying off the coast this afternoon and these will definitely push onto the south Washington and north Oregon coasts tonight. The surface pressure pattern suggests they may be less solid on the central coast around Newport tonight, but viewing of the eclipse from Newport could be a little iffy Monday morning. The low clouds will likely push inland along the Columbia River later tonight and early on Monday to Kelso with some clouds trying to reach the Vancouver and Portland areas. Believe the clouds in the Vancouver and Portland area will mainly be scattered before mostly clearing before the main part of the eclipse, though a brief ceiling is possible near KTTD Monday morning. Farther southward in the Willamette Valley conditions will stay mostly clear for the eclipse on Monday morning. Some smoke from fires in the Oregon Cascades could drift west on Monday but this will be slow to occur and probably not affect eclipse viewing. Otherwise Monday afternoon will be sunny as the morning clouds clear to a little ways off the coast under a building upper ridge. The air mass will be warming, and coastal temperatures could reach the lower 70s in areas, with upper 80s and lowers 90s common inland except mid 80s near Kelso. The upper ridge starts to move off to the east Tuesday, but it is still close enough for another warm day inland Tuesday with temperatures in the mid 80s to around 90. We don`t expect much in the way of lower clouds inland on Tuesday, though the coast will see increasing lower clouds that may persist or hug the coastline much of the day. Southwest flow aloft will continue to increase Tuesday night and Wednesday as the upper ridge continues moving eastward and the next system approaches. This will mean persistent cloud cover at the coast, perhaps even some spotty drizzle, and more morning low clouds inland with resultant cooler temps. Temperatures inland will likely be close to or a bit below seasonal normals Wednesday. Some convection late Tuesday spreading north from a weak low over California might clip the Willamette Pass area, but southwest flow aloft will limit any coverage and how far north it can reach in our Cascades as it mainly spreads into central and eastern Oregon. The approach of the system Wednesday is making any chance of convection in that area looking less likely as the southwest flow aloft and the low level onshore flow increases. Tolleson .LONG TERM...Wednesday night through Sunday...Models are in good agreement a shortwave trough will slide eastward across British Columbia and Washington Wednesday night and Thursday. This should bring cooler temperatures, increased cloud cover and a chance of light rain, particularly along the coast and across the Cascade foothills, but even portions of the Willamette Valley could see some light rain. Shortwave ridging should then build over the Pacific Northwest and bring a return to more sunshine and above average temperatures towards next weekend. /Neuman/Tolleson && .AVIATION...VFR conditions remain at the coast and inland this afternoon. Expect a layer of marine stratus to move into the north coast this evening around 03-04z with MVFR cigs. Farther down the coast, expect some stratus to move in early morning around 10-12z, perhaps with broken IFR cigs for a few hours. Winds remain northerly on the central coast tonight then becomes a little north-northeast toward morning. Thus, confidence is not high in the amount of marine stratus on central coast. Current forecast is for broken IFR cigs, 11z-16z. Also expect some marine stratus to move up the Columbia River to around Kelso early Mon morning. There might get some clouds near PORTLAND around sunrise, but likely just scattered for a couple of hours, 12-16z time frame. PORTLAND AND APPROACHES...VFR conditions tonight and Monday. Marine stratus will push part way up the Columbia River tonight to around KLS with MVFR or even IFR cigs. May get some low clouds near PORTLAND, but likely just a scattered layer for a couple of hours, 12-16z time frame. && .MARINE...A persistent weather pattern will result in little change in the marine weather the next several days. High pressure holds over the NE Pacific while a thermal trough builds along the south Oregon coast. This supports north winds across the south Washington and north Oregon waters. The thermal trough strengthens each afternoon such that the north winds will increase and become gusty each afternoon. The winds south of Cascade Head will have frequent gusts to around 25 kt which supports the current small craft advisory for winds. The seas will be locally generated from these winds and generally remain 4 to 6 ft with periods at 9 to 10 seconds. The seas will be choppier in the southern waters for the afternoons with dominant periods possibly around 8 seconds. tw && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory for winds until 11 PM PDT Monday for Coastal Waters from Cascade Head OR to Florence OR out 60 nm. Small Craft Advisory for Rough Columbia River Bar from 3 AM to 7 AM PDT Monday. && $$ 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.