National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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-- Discussion containing changed information from previous version are highlighted. --761FXUS66 KPQR 280447AFDPQRArea Forecast DiscussionNational Weather Service Portland OR947 PM PDT Thu Jun 27 2024.UPDATED AVIATION DISCUSSION...&&.SYNOPSIS...Scattered showers continue through this evening asan upper level trough exits the region. Warm and dry conditionsreturn tomorrow, with temperatures warming into the upper 70sand low 80s for interior valleys and upper 60s along the coast.Another shortwave trough returns Saturday night into Sunday,bringing another 15-30% chance of showers, mainly for the coastand higher terrain. We`ll maintain consistently warm and dryconditions through mid-next week. Temperatures begin to riseThursday, but uncertainty remains with how warm we will get.&&.SHORT TERM...
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Now through Saturday...Now through Sunday...The back end of an upperlevel trough is pushing through the interior northwest as ofthis afternoon. As the trough exits our region, expect lingeringshower activity over higher terrain and interior valleys fromthe Portland/Vancouver Metro Area to Cowlitz County. AdditionalQPF amounts will be minimal, except the south WA Cascades wherethere could be some higher amounts around 0.10-0.20 inch.Cloud cover will gradually decrease for most places as thetrough exits tonight, except along the coast. Weak ridging willbuild tomorrow (Friday) over the Pacific Northwest, leading towarmer and drier weather. Inland winds turn more northerlytomorrow, supporting drier conditions. We`ll also see increasingsunshine across the area tomorrow, leading to warmer afternoonhighs in the upper 70s to low 80s for interior valleys. NBMsuggests a 15-25% chance of highs exceeding 85 degrees forinterior valleys. Meanwhile, northwesterly winds along the coastwill keep conditions mild, with forecast highs in the upper 60s.Saturday will remain warm and dry, with afternoon highs similarto Friday. Chances for afternoon highs exceeding 85 degrees inthe interior valleys increase slightly to around 35-40%. Windswill begin to turn more westerly as another upper trough nearthe Gulf of Alaska dips southward toward the Pacific Northwest.Not expecting impactful winds, but the strongest westerly windgusts will likely be in the central Columbia River Gorge around20-25 mph.Saturday night to Sunday, we`ll see increasing cloud cover asthe trough moves across the region. It`s not a very robusttrough, so conditions will be mostly dry. About a 15-30% chanceof showers is forecast along the coast and higher terrain asorographics will be the main forcing for showers. Any showeractivity will mostly occur Sunday morning. By Sunday afternoon,conditions dry out further and temperatures are forecast towarm-up near or slightly above normal. -Alviz.LONG TERM...Saturday Night through Thursday...Sunday night through Thursday...WPC clusteranalysis are in general agreement of upper level ridging overthe NE Pacific. Most ensemble members keep the ridge axis faroffshore of the West Coast, so the current long term forecastmaintains warm, dry weather with inland highs in the upper 70sto low 80s. Most ensembles keep this pattern through the middleof the next week, but 15% of members transition our region tomore zonal flow by Tuesday/Wednesday. If the pattern turns morezonal, we may see temperatures cool a few degrees. But for now,expect pleasantly warm and dry weather through at least mid-next week. Thursday, ensembles hint at temperatures warming upfurther due to high pressure building, but uncertainty remainswith how warm we will get. -Alviz
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Any lingering showers have come to an end as onshoreflow gradually weakens later tonight into Friday morning due tohigh pressure building offshore. Still expecting clouds to reformovernight as marine layer over region cools, with mostly VFRinland and a mix of VFR to MVFR along the coast - best chance forMVFR at KAST. As flow turns more northerly and then north-northeasterly on Friday, will see clouds across the interiordissipate between 15Z and 19Z, with clouds holding on bit longeralong the coast, especially north of Tillamook to Astoria. Onceconditions transition to VFR they`ll likely stay that way throughFriday evening.PDX AND APPROACHES...Onshore flow will weaken overnight intoFriday, but VFR CIGS of 4000 to 6000 ft persist. However latestHREF guidance does suggests a 30-40% chance for a period of MVFRCIGS between 12-16z. Then clouds will be break apart and clearout most likely between 16Z and 18Z with high confidence in VFRconditions through the afternoon/evening. -Schuldt
-- End Changed Discussion --&&.MARINE...Weak low pressure remains onshore this evening, withhigh pressure well offshore. Winds remain out the west tonorthwest tonight. As the offshore high builds, will see all windsturn north to northwest late tonight and Friday. At same time,thermal low pressure will remain over far southwest Oregon intonorthwest California. As such, will get back into some northerlywinds, with gusts up to 20 kt Friday through Saturday, mainlyduring the afternoons/evenings to south of Tillamook. Overall,seas staying in the 4 to 5 ft range.Yet another weak low pressure arrives later Sat, with windsflipping back to the west or southwest. Gradients weaker, so windsnot expected above 15 kt, while seas stay at 4 to 6 ft. Nextweek, will see high pressure offshore build, with return of gustynortherly winds on the waters for the afternoons/evenings. /Rockey&&.PQR WATCHES/WARNINGS/ADVISORIES...
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OR...None.WA...None.PZ...None.
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