FXUS66 KPQR 282048 AAA AFDPQR Area Forecast Discussion National Weather Service Portland OR 129 PM PDT Sat Sep 28 2024 .SYNOPSIS...Dry weather prevails through at least the middle of the next week. Cooler temperatures on Sunday with a weak disturbance, but not expecting any precipitation. High pressure builds early next week, leading a warm-up Monday and Tuesday. Confidence breaks down for the latter half of the week with cool, wet conditions possibly returning Thu/Fri. && .SHORT TERM...Now through Sunday...A very weak upper level trough is passing through Saturday and Sunday, but no precipitation is expected as there is no associated low-level feature. However, temperatures will be slightly cooler, and RH values remain relatively high. Sunday only sees a 25-40% chance of high temperatures in the Willamette Valley exceeding 70 degrees. However, warmer conditions are over the horizon as a ridge begins to move in near the end of Sunday into Monday morning. Westerly onshore winds also pick up Saturday night, with possibly stronger westerly winds in the Columbia Gorge up to 30 mph. The Willamette Valley won't see as strong wind, and likely gusts won't exceed 10-15 mph. Winds greatly weaken going into Sunday daytime hours. Breezy northerly flow up to 20 mph is possible in the central and southern Willamette Valley Sunday afternoon. A thermal trough develops Sunday night, allowing for a brief period of easterly offshore flow, with gusts up to 25 mph possible at the Columbia Gorge and east-west aligned channels in the Cascades. Offshore flow looks to last through Monday night. /JLiu .LONG TERM...Monday through Friday...WPC clusters continue to show high confidence (+90%) that ridging will build across the eastern Pacific and toward the West Coast to start next week. By Tuesday, the ridge will build farther inland into the Great Basin Region and the Rockies, with the axis closer to the coast. This will support a warming trend back to average on Monday with highs in the low 70s inland and 60s along the coast. Tuesday will see a jump back 5-10 degrees above normal with highs in the upper 70s inland and upper 60s to low 70s for the coast. Models indicate another thermal trough developing across the area Sunday night and persisting into Tuesday which will support offshore flow across much of northwest Oregon and southwest Washington. NBM suggests a 10-20% chance of wind gusts meeting or exceeding 25 mph for most areas. The highest chances of 40-60% are along the Columbia River Gorge, exposed peaks/ridges near the Gorge, and the Cascade crest. Offshore flow will also lead to daytime RH falling near 25% for portions of the high Cascades Monday and Tuesday along with poor RH recoveries Monday night. By Tuesday afternoon, models suggest that the thermal trough will break down and onshore flow will return. Dry weather will prevail as high pressure lingers overhead. Wednesday to Thursday, the majority of ensemble members from WPC cluster analyses show a ridging/zonal flow pattern with above average 500 mb heights. In this case, we would continue to experience warm and dry fall weather. Slightly better agreement on troughing returning next Thursday night into Friday morning, with some better potential for rain showers and cooler conditions to return then. -Batz/Alviz && .AVIATION...Dry southwest flow aloft ahead of an upper level trough that will push some high clouds across the region today. Widespread VFR conditions expected across the area. Near the central Oregon coast, including KONP, there is around a 20-40% chance of MVFR conditions through 02z Sunday. Onshore flow in the lower levels will maintain northwest winds up to 10 kt through this evening. Low level flow turns slightly offshore along the coast Sunday morning. PDX APPROACHES...VFR expected through the TAF period, with increasing high clouds this afternoon. Northwest winds increase to around 8 kt later this afternoon. /DH && .MARINE...High pressure centered offshore gradually strengthens as it pushes northeast toward the Washington coast this weekend. Thermal troughing shifts farther south along the southern Oregon coast through Sunday. This will weaken the pressure gradient across the coastal waters tonight through Sunday, causing the northerly winds around 15-20 kt to decrease further through Sunday morning. Pressure gradients begin to strengthen again by Sun night with gusts up to 20-25 kt possible for the coastal waters south of Cascade Head. Breezy northerly winds again expected early next week as the thermal trough strengthens along the Oregon coast. As of noon Saturday, seas have fallen below 10 ft at buoy 46029 while at buoy 46050 seas persist around 10 to 12 ft. Seas are expected to continue to subside as the northwest swell decreases and winds ease, falling to around 6 to 8 ft by Sunday morning. Seas continue to subside to around 4 to 6 ft on Monday. The next strong weather system is expected to stay to the north, with low pressure moving into the Gulf of Alaska early next week. A weak front associated with this system will approach the waters late Tuesday. Also with this system, a developing northwesterly swell will likely push seas up again over 10 ft across the coastal waters beginning late Tuesday and continuing through Wednesday. Latest guidance shows a 10-30% chance of wave heights exceeding 15 ft across the northern coastal water zones. /DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory until 5 PM PDT this afternoon for PZZ252- 253. Small Craft Advisory until 8 PM PDT this evening for PZZ271. Small Craft Advisory until 11 PM PDT this evening for PZZ272-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland