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. --828FXUS66 KPQR 290447AFDPQRArea Forecast DiscussionNational Weather Service Portland OR947 PM PDT Fri Jun 28 2024.UPDATED AVIATION DISCUSSION...
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.SYNOPSIS...Aside from some light drizzle across the northernportions of the CWA late Saturday into Sunday, onshore flow willmaintain near average temperatures into early next week. There is30-40% chance that stronger high pressure offshore will shift overthe region towards the end of next week and bring our hottesttemperatures of the Summer so far.
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Tonight through Sunday...Weak upper leveltroughing under low level onshore flow will keep the area mainlydry with temperatures pretty darn close to average for thistime of year through the weekend. A passing shortwave trough toour north will clip the region and perhaps deepen the marinelayer enough to wring out some drizzle and light rain alongmainly the coast, Coast Range and Cascades north of a lineextending between Mt Jefferson and Newport late Saturday intoSunday. NBM probabilities for rain only climb into the 15-30%range for any given 6-hour period late Saturday into Sundayalong the north coast and higher terrain. All in all, it lookslike rather average and benign weather for late June. /Neuman.LONG TERM...Monday through Friday...As the upper level shortwavetrough moves east of the region early next week, WPC clusters are invery good agreement of upper level ridging building over the easternPacific. Ensembles are in good agreement that zonal flow aloft andlow level onshore will couple to bring a continuation of temperaturesnear to slightly (a few degrees) above average for areas away fromthe coast through midweek.Uncertainty in the forecast begins to grow dramatically midweek asensemble members begin to diverge substantially on potentialscenarios. While nearly all of the ensemble guidance has aboveaverage 500mb heights over the Pacific Northwest by Thursday, about25% of the ensemble guidance suggests an upper level trough willeither be approaching the region from the northwest or a differentshortwave trough will be lingering across the northern Rockies tokeep temperatures across the area near average. The rest suggest apattern conducive for above temperatures, but with varying degrees ofheat. At this point, it appears there`s a 25% chance thattemperatures climb to 90F by Thursday across inland valleys with theprobabilities rising to 50% on Friday. There is even a lowprobability (10%) of 100F temperatures by Friday. The NBMdeterministic forecast is on the warm side of the probabilitydistribution come next Friday, but not enough to change it so haveleft the forecast as is. /Neuman
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High pressure continues to shift eastward as a weakupper-level trough approaches the coastline expected to clip theregion to the north on Saturday. Fortunately VFR conditions likelypersist at inland sites through the TAF period with CIGSeventually lowering to ~5kft by Saturday evening. That said, thesame can`t be said for the coast where MVFR conditions developbetween 20-23z due to the aforementioned weather disturbance,deteriorating further to IFR cigs/vis by Saturday eveningalthough confidence is only moderate regarding the exact timing atKONP/KAST.PDX AND APPROACHES...High pressure shifting eastward will continueto facilitate VFR conditions locally with typical diurnallydriven northwest to northerly winds through 00-06z Sunday. CIGSgradually decrease through the period but will remain VFR.-Schuldt
-- End Changed Discussion --&&.MARINE...Weak high pressure over the northeast Pacific with lowersurface pressure over California and the Great Basin will more orless maintain itself into next week. A weak front will temporarilytry to clip the waters tonight into Saturday and turn winds moreout of the west. Otherwise, expect north to northwest windsacross the waters with the strongest winds generally off thecentral coast of Oregon and lighter winds farther north. Windswill generally peak in the afternoon and evening hours each day.Pressure gradients appear increasingly likely to increase by earlyto mid next week so that there is a >90% chance that northerlywind gusts of 25-30 kt spread northward across the waters. Thiswill in return develop steep wind driven seas of 5-8 ft with adominant period of 7-8 seconds by Tuesday or Wednesday. /Neuman&&.PQR WATCHES/WARNINGS/ADVISORIES...OR...None.WA...None.PZ...None.&&$$www.weather.gov/portlandInteract with us via social media:www.facebook.com/NWSPortlandwww.twitter.com/NWSPortland