Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 202307 AFDPQR Area Forecast Discussion National Weather Service Portland OR 306 PM PST Thu Feb 20 2020 .SYNOPSIS...Varying degrees of high pressure over the Pacific Northwest will bring cool nights, mild days, and mainly dry weather through next week. The main exception to this will be on Sunday into Monday when a storm system will bring the return of valley rain and mountain snow. && .SHORT TERM...Tonight through Sunday...Water vapor satellite imagery continues to show a closed upper level low dropping southward off the California coast, with shortwave ridging over the Pacific Northwest. Aside from some mid and high clouds streaming over the region this afternoon conditions remain rather mild. Expect these conditions to generally continue through Saturday. The exception to this will be the increase of marine clouds along the coast starting Friday as onshore flow takes over ahead of an incoming shortwave disturbance. Guidance continues to show a weak front brushing by the far northern portions of the forecast area on Saturday which could bring some light rain to areas north of the Columbia River. A much stronger front looks to then move across the forecast area late Saturday into Sunday. This front will bring the return of widespread valley rain and mountain snow on Sunday, with snow levels lowering below Cascades Passes. There is still some uncertainty with QPF and snow amounts over the weekend, but based on the latest guidance it still looks like advisory level snow is possible over the North Oregon and South Washington Cascades. /64/Neuman .LONG TERM...Sunday night through Wednesday...Models and their ensembles are in good agreement the shortwave trough impacting the Pacific Northwest on Sunday will slide eastward and be replaced by shortwave ridging. This will result in decreasing showers and clouds across the area Sunday night into Monday. There is strong consensus the Pacific Northwest will then be under the influence of a shortwave ridge for much of next week. This will bring cool nights, high temperatures near average and mainly dry weather. Various operational and ensemble members do suggest a shortwave trough will try to slide into the ridge towards the middle of next week and potentially bring light precipitation to the area. However, there`s very little consensus on how this might take shape and when exactly it will occur among model and ensemble guidance. As a result, the NBM slight chance PoPs towards the end of the long term forecast seem reasonable given the pattern and uncertainty. /Neuman && .AVIATION...High pressure persists creating VFR conditions through Fri. Gusty east winds continue through the Gorge and Coast Range through 00Z Fri when the pressure gradient weakens. Winds will generally become light and variable through the valley after 08Z Fri. Slight chance of patchy fog around sunrise at 13Z Fri, but with a dry boundary layer, chances are low. If it does form, it would be near KEUG and other fog prone areas. KPDX AND APPROACHES...VFR conditions with gusty east winds. Strong east winds around 2000 ft AGL will persist through 06Z Fri. Potential for some patchy fog around the airport in the early morning Fri, but unlikely due to winds through the evening. Not included in TAF. -Muessle && .MARINE...High pressure remains over the area with a westerly swell through Sat morning. Seas around 5 ft will persist through Sat evening with winds generally calm. Sat night, a 990 mb low off the Alaska Peninsula will move south towards the CONUS Pacific Northwest. While the low will stay north of the area over the AK-PEN, winds and seas are expected to ramp up. The main portion of this system will move over the waters Sun afternoon. With a strong gradient, small craft level winds with strong southerly gusts up to 30 kt are likely. Seas will also build to near 10 ft Sat afternoon, rising to near 16 ft Sun afternoon. With this system, there is still quite a bit of uncertainty due to model differences with the intensity of the low (how deep it is), and where it will track. In any case, a more active pattern is expected this weekend. By Mon night, conditions should settle and weak high pressure will develop over the Pacific creating calm conditions once again. -Muessle && .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 nm offshore. This area is commonly referred to as the forecast area.

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