Area Forecast Discussion
Issued by NWS Portland, OR

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000 FXUS66 KPQR 270225 AAA AFDPQR Area Forecast Discussion...UPDATE National Weather Service Portland OR 724 PM PDT Mon Oct 26 2020 Updated the marine and aviation discussions .SYNOPSIS..High pressure will build in over the Pacific Northwest through the middle of this week. This will bring dry weather along with temperatures slowly warming. A weak front towards the end of this week brings the next chance for rain. && .SHORT TERM...Tonight through Thursday...Sky cover and temperatures are the main forecast challenge in the short term as dry weather persists under high pressure and light winds. Temperatures will gradually moderate closer to what is normal for this time of the year. Satellite imagery shows marine stratus over the NE Pacific banking up to the Washington coast late this afternoon. These low clouds are ahead of a east-west oriented front well north of Washington. The forecast models show that the marine stratus will move southward tonight and Tuesday as the front shifts further south. The front will remain north of the Portland forecast area as high pressure holds over the Pacific NW and NE Pacific, but the low clouds ahead of it will likely move into SW Washington and extreme Northwest Oregon tonight, and possibly further south into western Oregon on Tuesday. A thermal trough along the SW Oregon coast tonight with higher pressure to the NE, may maintain enough of an offshore component to the winds to prevent the stratus from moving onto the central Oregon coast tonight. Light north winds moving through the interior valleys though, will likely move any stratus that may make it to the north Willamette Valley tonight further south into the Willamette Valley Tuesday morning. The forecast confidence of the stratus making it to Salem is low, and really do not think the clouds will make it to Eugene. Regardless, the interior valleys will likely clear in the afternoon and daytime highs will likely warm into the mid to upper 50s. There will be little change Tuesday night and Wednesday, with some stratus moving inland Tuesday night into Wednesday. High pressure weakens Wednesday night and Thursday allowing another warm front well north of the area to move southward and likely bringing stratus into SW Washington and NW Oregon. Have updated the sky cover and temperature forecasts this evening to account for the increasing chance of diurnal marine stratus. ~TJ .LONG TERM...No Changes. Previous discussion follows...Thursday night through Monday...Models are continuing to agree that Friday is the next chance for precipitation, as a cold front looks to impact the area, temporarily breaking the hold of the high pressure which has been the dominate synoptic feature. The models are in general agreement as to the timing and location. However, there remains enough differences in precipitation between operational model families as they continue to show this cold front weakening each successive run. Next weekend operational models are supported by ensembles, as they show the ridge of high pressure rebuilding. This will likely lead to dry weather returning for most of the area. /42 && .AVIATION...Satellite imagery Tuesday evening shows an area of MVFR marine stratus with cigs generally between 2000 and 3500 ft quickly moving southward down the Washington coast and through the Puget Sound. Expect this area of stratus to continue pushing southward tonight, moving into the south Washington and north Oregon coast between 02-06Z Tuesday and then the central Oregon coast between 06-12Z. It appears stratus will also move down the Cowlitz Valley and into the northern Willamette Valley late tonight, and possibly into the central valley as well. The biggest forecast challenge for the 06Z TAF cycle is expected cigs at KSLE and KEUG tonight into Tuesday morning, as there is some uncertainty in regards to how far south the stratus will make it tonight. The latest trends suggest stratus may be able to push to the south of KSLE, possibly approaching KEUG. Stratus should scatter out some Tuesday afternoon, before redeveloping and expanding across the entire Willamette Valley Tuesday night. For detailed regional Pac NW weather information, go online to: KPDX AND APPROACHES...Scattered to broken MVFR stratus will most likely move into the KPDX terminal early Tuesday morning, by 15Z at the latest. At least some scattered clouds with cigs around 3000 ft may linger through Tuesday afternoon before skies become overcast later Tuesday night with cigs around 2000 ft. -TK && .MARINE...High pressure offshore will maintain northerly winds across the waters over the next several days, with the strongest winds expected over the coastal waters south of Cascade Head. Seas will stay in the 3 to 6 ft range, with the highest seas well offshore. Do not expect much change in this pattern through early Thursday. A front will approach the region later Thursday and shift across the coastal waters Thursday night. This will bring the return of light to moderate southerly winds to the waters on Friday, sustained around 15 to 20 kt. Seas will see a bump upward, but will most likely peak between 6 and 9 ft Friday night. Seas and winds should east this weekend. -TK/Rockey && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ Interact with us via social media: is the U.S. government's official web portal to all federal, state and local government web resources and services.