Area Forecast Discussion
Issued by NWS Portland, OR
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140FXUS66 KPQR 110923AFDPQRArea Forecast DiscussionNational Weather Service Portland OR223 AM PDT Sun Aug 11 2024.SYNOPSIS...-- Changed Discussion --
Westerly onshore flow will continue through thisweek, bringing a cooling trend along with increasing morningclouds and chances for light rain or drizzle at the coast.Temperatures will fall to near or just below normal by Sunday,lasting through next week. Onshore flow will also bringimproving air quality for most locations as smoke will be pushedto the east, aside from areas immediately near and/or downwindof ongoing wildfires. The return of rain chances is possiblelate this week, though amounts look to be limited at this time.-- End Changed Discussion --
&&.SHORT TERM...-- Changed Discussion --
Sunday through Saturday...Observations earlySunday morning indicate onshore flow continues across NW Oregonand SW Washington with west to northwesterly winds under fairlyzonal upper level flow. Satellite imagery shows marine stratuspushing east along the western Coast Range foothills andfiltering inland along the Columbia River valley into thePortland metro area and through Coast Range gaps. HREFindicates a 40-60% chance of stratus filling in the WillametteValley by daybreak and slowly dissipating late morning throughearly afternoon. A weak trough will begin deepening along theWashington & Oregon coasts today, and this combined with thecloud cover will allow daytime temperatures to fall back to nearnormal today, low 80s in the Willamette Valley.This upper trough continues deepening along the Westerncoastline Monday before moving inland Tuesday. Daytimetemperatures will continue cooling to below normal Monday andremain fairly steady Tuesday with mid to upper 70s acrossinland valleys and low to mid 60s across the coast.Additionally, some moisture associated with this trough willallow for chances of drizzle and light rain along the coast latetonight through early Tuesday. Could also see some drizzle overthe Cascades as the marine layer deepens under continuedonshore flow. NBM notoriously has a difficult time capturingdrizzle chances inland, so NBM PoPs remain less than 10%.However, if any drizzle does occur over the Cascades,accumulation would be very light.Wednesday`s weather will be similar to today with temperaturesbouncing back to near normal under relatively zonal flow andmorning stratus under continued onshore flow. Ensemble guidanceis in good agreement of the general upper level pattern latethis week with all WPC 500mb clusters indicating longwave troughingdeveloping Thursday and continuing into the weekend with thepotential for multiple waves along the trough. Overall, thispattern is likely to bring the return of rain chances for muchof the CWA as well as below normal temperatures. However,uncertainty still remains within the ensembles and deterministicmodels in the specific location and timing details of the maintrough and associated shortwaves, which is causing lower NBMPoPs than expected. Latest guidance is indicating an amplifiedwave moving west into Oregon on Thursday with confidenceincreasing in showers and an isolated chance of thunderstormsover the central Oregon Cascades. More widespread rain ispossible Friday and Saturday depending on the timing of the nextwaves pushing into the region from the northwest. At this time,rain amounts look to be pretty limited at less than 0.1-0.25inch for most areas, but we will have to keep an eye on thispattern. -HEC-- End Changed Discussion --
&&.AVIATION...-- Changed Discussion --
Weak westerly flow aloft today while onshore flowpersists in the lower levels. Marine stratus again solidly filledin along the coast with CIGs holding around 400-800 ft. Theprofiler at Astoria also shows the marine layer has deepened toaround 3000 ft with some drizzle being reported at KAST. Expect atleast IFR conditions to persist at the coast through 18-20ZSunday, while there remains around a 40% chance of CIGs falling toLIFR early this morning. Northwest winds with gusts up to 20 ktthis afternoon for the central OR coast.Inland, again predominately VFR expected through the period, but astronger marine push up the lower Columbia has caused MVFRstratus to develop at KPDX and KTTD as of 09Z Sunday. CIGs aroundFL015 will likely persist there through 18Z this morning. Stratusmay continue to filter across the Willamette Valley this morning,with probabilities around 60% for KUAO, and 30-40% for KSLE andKEUG. NNW winds up to 10 kt inland this afternoon and evening,except stronger through Coast Range gaps.Smoke from wildfires burning across the region could result insome slant range visibility issues.PDX AND APPROACHES...MVFR stratus with CIGs around FL015 expectedto persist through 18-19Z Sunday. Then, VFR expected withincreasing high level clouds through this evening. Northwestwinds increase up to 8-10 kt this afternoon and evening. /DH-- End Changed Discussion --
&&.MARINE...-- Changed Discussion --
High pressure offshore will maintain north to northwestwinds up to 15 kt across the coastal waters Sunday. Seas remainchoppy and primarily wind driven around 5 to 6 ft today. Then, thesurface high retrogrades west as a weak front drops south of ofthe Gulf of Alaska on Monday. A broad area of weak low pressurenear Vancouver Island causes winds across the coastal waters toshift more westerly on Monday, and veering southerly on Tuesday.Seas expected to subside to around 2 to 4 ft by Tuesday. Fairlybenign conditions continue into Wednesday. /DH-- End Changed Discussion --
&&.PQR WATCHES/WARNINGS/ADVISORIES...OR...None.WA...None.PZ...None.&&$$www.weather.gov/portlandInteract with us via social media:www.facebook.com/NWSPortlandx.com/NWSPortland
