Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 242217 AFDPQR Area Forecast Discussion National Weather Service Portland OR 317 PM PDT Sat Oct 24 2020 .SYNOPSIS...A few remaining showers but skies are beginning to clear. High pressure over the Pacific expected through mid next week. Gusty winds expected today through early Sunday morning bringing in ample cool air from the Columbia Basin. Likely temperatures will be cooler Sunday night before slowly warming on Monday through mid week. Settled weather through Wednesday. && .SHORT TERM...Tonight through Tuesday...Satellite still shows the remnants of the low that was moving southeast along the Oregon coast this morning, although it is quickly moving out of the area. The westerly flow associated with this passing system is beginning to shift northeasterly along the north coast while the central coast remains westerly. Some lingering showers are present this afternoon especially around where the Willamette and the Columbia River intersect. This likely is due to some meso-scale convergence of two different air masses: easterly flow through the Gorge and more of a northerly wind coming down from Washington. The jet stream aloft is generally meridional with the area sitting in the right exit region of the 130 mph jet streak. This jet will enhance the high pressure that is building over the Pacific, and encourage a trough of cooler air to push down from Canada along the northern Rockies. This pattern of high pressure over the Pacific and a cool air digging trough is commonly associated with strong easterly winds; while in essence similar to the wind event that occurred in early Sept, it is not going to be nearly as strong. Winds will likely be the most intense this evening into tomorrow as the cool air reaches it`s "peak" low temps. The easterly winds combined with the cool air pooling in the Columbia Basin sets the area up for a few cold nights tonight and Sunday. Sunday is expected to be the chilliest night due to the stronger winds today which will help inhibit as much radiational cooling. Still can expect surface temps just above freezing tonight. By Sunday, the winds will ease and conditions will be clear and dry. Easterly winds will prevail through the northern portions of the forecast area while through the southern Willamette Valley will likely be more northerly. With clear skies and lighter winds, Sunday night will be the coolest night of the weekend. Many areas below 2000 ft will see temperatures around 25-30F inland and 30-35F along the coast. Being at the tail end of the growing season, decided to issue a freeze watch for many interior locations. Clear skies and quiet weather will persist through Tuesday. -Muessle .LONG TERM...Tuesday night through Friday...Towards the middle of the week is when the forecast becomes a bit more fuzzy. Tuesday night into Wednesday conditions will continue to be dry and generally clear. By late Wednesday, some models are beginning to show the signs of the ridge weakening and flatting out with a long-wave trough advancing towards the area from the Gulf of Alaska. However, there is quite a bit of model uncertainty at this time. Recent runs have shown this system slowing and not really reaching the area until Thursday night. With that said, there are discrepancies regarding both the timing and the track of this trough. Decided to stay conservative both with the onset and track of this system. -Muessle && .AVIATION...Weak low pressure along the Oregon coast will push further southward tonight, with building high pressure over eastern Washington. Plenty of VFR clouds from the coast mtns eastward across the Cascades and east slopes. As the offshore flow increases, expect continued gradual decrease in these clouds this afternoon through this evening. With building high east of the Cascades, will have increasing north to northeasterly winds across the area into tonight, and continuing through Sunday. The strongest winds will be later tonight into Sunday am, with east to northeast gusts 25 to 35 kt over the higher terrain and coastal areas, but gusts 35 to 45 kt likely in the western Columbia River Gorge, as well as near passes of the Cascades. Inland areas to south and north of Portland likely to have breezy winds, but think 10 to 20 kt at most. No concerns for LLWS, as winds aloft stay east to northeast. Just bumpy at times. For detailed regional Pac NW weather information, go online to: http://weather.gov/zse KPDX AND APPROACHES...Clouds over area will gradually break up this afternoon into early evening, with scattered clouds by 01Z, and clearing after 06Z. Offshore flow with east winds through Sunday, though strongest winds expected from late this evening through mid-morning Sunday, with gusts 30 kt at times. No LLWS expected as winds aloft remain east to northeast. Just bumpy at times. -Rockey && .MARINE...Low pressure near Florence will continue drifting south this evening. Building high pressure over the inland Pac NW will bring increasing east to northeast winds to the coastal waters this afternoon through Sunday. Should see gusts 25 to 30 kt at times this afternoon through Sunday, with strongest winds likely in areas downwind of the gaps in the coastal terrain. Will maintain current Small Craft Advisory. Winds will ease later Sunday as offshore pressure gradients start relaxing. By Monday, northerly flow develops as high pressure over the NE Pacific nudges closer and the inland Pac NW high shifts farther away. From mid week onward the high pressure weakens as low pressure systems move into B.C. Seas of 8 to 10 ft this afternoon will continue to subside, with 6 to 7 ft this evening, and down to 4 to 6 ft for Sun. The increased east to northeast winds later today into Sunday will create locally choppy seas at times. High pressure over the offshore waters will dominate weather to start next week, with lighter northerly winds and seas running 3 to 5 ft. Changes arrive later next week, as series of fronts approach the region. Too early for much in details, but suffice to say will see return of southerly winds by Thu and Fri. -Rockey && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT Sunday for all coastal waters from Cape Shoalwater to Florence. && && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT Sunday for coastal waters from Cape Shoalwater WA to Florence OR out 60 NM. Small Craft Advisory until 2 PM PDT this afternoon for Columbia River Bar. && $$ Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland

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