Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
519 FXUS66 KPQR 261204 AFDPQR Area Forecast Discussion National Weather Service Portland OR 504 AM PDT Thu Sep 26 2024 .SYNOPSIS...Quiet, seasonable conditions expected today aside from lingering fog during the morning. Another weaker front arrives overnight late today into Friday morning. High pressure returns over the weekend. A slight warm up back to slightly above average possible early next week. More active weather possible mid next week. && .SHORT TERM...Now through Saturday...With the passage of a cold front yesterday, PNW is now in a post frontal airmass. Clear skies and calm winds have allowed temperatures to drop into the upper 40s to low 50s so far and combined with the wet ground from yesterdays rains have produced patchy areas of fog across northwest Oregon and southwest Washington. Nighttime microphysics satellite imagery as of 1030Z along with ASOS observations show fog expanding throughout the Willamette Valley, prompting a Dense Fog Advisory until 11 AM. Dense fog is possible during the morning commute so slow downs are possible. The system that brought rain to the area yesterday will lift northeast, leaving quasi-zonal flow across the region for most of Thursday. Conditions will be dry with seasonable temperatures in the low to mid 70s inland and mid to upper 60s along the coast. A weaker cold front associated with a low coming onshore across central British Columbia will bring a chance for light rain showers late Thursday. The best chance for rain will be across southwest Washington and the Coast Range of Oregon with generally a few hundredths expected and up to a quarter inch locally. Friday and Saturday are both expected to be around average temperature-wise. Friday could see some gusty north winds as high pressure over the northeast Pacific builds towards the PNW, tightening the pressure gradient across the region. Gusts around 30 mph will be possible along the coast and 15-20 mph inland. Upper level flow shifts southwest as a large trough approaches from the west. Models show a weak thermal low developing across western Oregon late Friday along with weak offshore flow east of the Willamette Valley, Friday night into Saturday morning. The pressure gradient between The Dalles and Troutdale is expected to be around -2 to -3 mb so easterly winds around 10 to 15 will be possible during that period. -Batz && .LONG TERM...Saturday Night through Wednesday...The surface high moves eastward over Washington and Oregon while a trough moves overhead in the upper levels. This will bring below average temperatures in the upper 60s inland and upper 50s along the coast for Sunday. A dampened ridge is expected to develop across the West Coast which will support an upward trend in temperatures to Start next week. Approximately two thirds of the WPC clusters support this pattern with the remaining third supporting ridge development offshore. If the ridge sets up onshore, temperatures inland will reach the mid to upper 70s for Monday and Tuesday with mid to upper 60s along the coast. Confidence wanes into the middle of next week with approximately one third of the members depicting each of the following solutions, ridging offshore, ridging centered over the Great Basin, and the last with the ridge toward the center of the country and zonal flow across the PNW. Next week is very much up in the air at this time. Another weak thermal low could develop Monday through Tuesday which could support weak offshore flow at times east of the Willamette Valley. -Batz && .AVIATION...Westerly flow aloft with high pressure in place over the area. Cool and moist conditions at the surface will likely produce widespread, potentially dense fog this morning. The fog and/or stratus is expected to dissipate around 16-18z later this morning, with widespread VFR conditions returning to the area. Southerly winds are expected to increase along the northern OR coast this afternoon, with gusts up to 20 kt. A weak front will push toward the coast later today with chances for MVFR and IFR stratus increasing (>80%) after 04z Friday. PDX APPROACHES...VFR as of 10z, but fog is developing quickly at surrounding terminals and should push into KPDX by 12z. IFR conditions likely through at least 16z, then fog lifts and eventually scatters out by 17-19z. VFR expected this afternoon through at least 06z Friday. A weak front will likely push low clouds into the area with a 50-70% chance of MVFR CIGs between 09-12z Friday. Generally expect southeast winds up to 5 kt. /DH && .MARINE...A 983 mb low in the far NE Pacific will continue to strengthen as it moves toward Haida Gwaii today. Southerly winds will gradually increase as the frontal system associated with this low approaches the coastal waters. The strongest winds are expected across the northern zones, peaking this afternoon and evening with gusts up to 30 kt, except for the northwest corner of PZZ271 where gusts to 35 kt are likely between 2 PM and 8 PM PDT. Will maintain a high-end Small Craft Advisory for the coastal waters generally north of Cape Falcon through this evening. The trailing cold front is expected to weaken as it moves across the coastal waters tonight. Seas within the zone of strongest winds today are also likely to become steep and potentially hazardous, building to around 8 to 12 ft. A westerly swell moving in behind the front is expected to continue to build seas to around 12 to 15 ft tonight through Friday. High pressure also rebuilds on Friday, along with a strengthening thermal trough along the southern Oregon coast. This will result in a return to gusty northerly winds. Gusts up to 30 kt are very likely (80-90% chance) off much of the central Oregon coast. The westerly swell combined with northerly winds will likely create a chaotic sea state. A Small Craft Advisory has been issued for Friday and Friday night, but will need to monitor for the potential to be upgraded to a Hazardous Seas Warning. Northerlies are expected to continue through the weekend, while seas settle to around 8 to 10 ft. Seas likely subside further into early next week. /DH && .PQR WATCHES/WARNINGS/ADVISORIES.. OR...Dense Fog Advisory until 11 AM PDT this morning for ORZ108>118. WA...Dense Fog Advisory until 11 AM PDT this morning for WAZ204>207. PZ...Small Craft Advisory from 5 PM this afternoon to 5 PM PDT Friday for PZZ210. Small Craft Advisory from 2 PM this afternoon to 5 AM PDT Saturday for PZZ251. Small Craft Advisory from 5 AM Friday to 5 AM PDT Saturday for PZZ252-253-273. Small Craft Advisory from 11 AM this morning to 5 AM PDT Saturday for PZZ271. Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Saturday for PZZ272. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland