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. --724FXUS66 KPQR 302241AFDPQRArea Forecast DiscussionNational Weather Service Portland OR330 PM PDT Sun Jun 30 2024.SYNOPSIS...
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Onshore flow will maintain near to slightly above averagetemperatures through midweek. Building high pressure over the easternPacific and Pacific Northwest will bring a 60-70% chance for thehottest temperatures of the Summer so far by the end of the workweek.
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Tonight through Wednesday...In the short term, visiblesatellite imagery and radar reveal a few very light showers overmainly the north Oregon Coast Range and Willapa Hills. The convectionappears to be capped well below 700mb, which is limiting rainfallgeneration and resulting in mostly shallow cumulus clouds formingover the region. Meanwhile, visible satellite imagery reveals a weaksurface trough off the Oregon coast that models agree will shifttowards the coast overnight. Some HREF members and global ensemblemembers suggest light showers will return the coast late tonight intoMonday morning. Any rainfall amounts appear most likelyto be a couple hundredths of an inch or less. Another round of areasof fog will once again develop over the waters and along portions ofthe coast.Otherwise, an upper level shortwave trough will slowly shift eastwardaway from the Pacific Northwest early this week. This process willresult in only a very gradual warming trend through midweek withtemperatures remaining near to slightly above average during thisperiod. /Neuman.LONG TERM...Thursday through Sunday...The global ensembles appear tobe converging on a solution that results in high pressure shiftingover the Pacific Northwest late in the work week into next weekend.However, there are still some differences in the magnitude of theridge and the timing of the ridge. The net result is that therestill remains a fairly wide range of possibilities for temperatures,particularly on any given day with the main uncertainty revolvingaround which day will be the hottest, and perhaps more importantly,the duration of the heat.The most likely scenario (generally a 60-70% probability) is that weheat up enough to experience our hottest temperatures (at least thelow to mid 90s) of the Summer so far by Friday or Saturday. However,the probabilities for 100F temperatures are not insignificant andcurrently lie around the 40-50% range per the NBM for Friday andSaturday in the Willamette Valley. Note there is a small subset ofthe global ensembles that produce 100s on Friday and Saturday thatkeep us locked in a pattern that keeps 100s around well into thefollowing week for a long duration heatwave. At this point, thisscenario appears to have a low probability (~10-20%) of coming tofruition, but it`s not certainly not a zero percent chance ofhappening either.On the opposite side of the spectrum, there is a small subset of theensemble guidance (~10-20%) that suggests ridging will be shortlived and/or low amplitude enough to make 90F difficult to achieveon any given day between Thursday and Saturday. Overall, NBMtemperature and RH values appear completely reasonable given theuncertainty in exactly how hot the area will get and the magnitudeof the ridge (and height of the resulting subsidence inversion) sostuck with the deterministic NBM throughout the extended. /Neuman
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Onshore flow continues this afternoon with VFRconditions prevailing. There is some convection over the area, butmoisture is shallow so showers are not very strong. Convectionwill diminishes this evening as will cloud cover. Expect low VFRto MVFR to form inland overnight with a 20-60% chance for MVFRcigs after 12-14Z Mon through about 18Z Mon. The higher chancesfrom about KSLE to KEUG and around the KPDX area.At the coast fog/low stratus already beginning to stick along thecoast and is expected continue to fill in this evening (80-90%chance) from around 00-03Z Mon through 16-18Z Mon.PDX AND APPROACHES...VFR expected through 18Z Mon, but there is a40-50% chance for MVFR cigs 2000-3000 ft 13-16Z Mon. For now willkeep MVFR conditions out of KPDX, but have it at KTTD. /mh
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Weak high pressure over the northeast Pacific with lowersurface pressure over California and the Great Basin will more orless continue through the week. A weak area of surface lowpressure will pass over the area through tonight, supportinginitially southwest winds before turning to the west in its wake.Otherwise, expect north to northwest winds across the waters ashigh pressure strengthens toward the middle of next week, with thestrongest winds generally off the central coast of Oregon andlighter winds farther north. Winds will generally peak in theafternoon and evening hours each day. For now have issued a SmallCraft Advisory for the central zones, but may need to expandfurther north. Because as a thermal low develops along thenorthern California/southwest Oregon coast on Tuesday andstrengthening/spreading north into Wednesday and thereafter. As aresult will see an increase the pressure gradient along the coastand over the waters with a >90% chance that northerly wind gustsof 20-30 kt spread northward across the waters by mid week. Thiswill in return develop steep wind driven seas of 5-8 ft with adominant period of 7-8 seconds by late Tuesday or Wednesday./mh -Batz
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OR...None.WA...None.PZ...Small Craft Advisory from 5 PM Monday to 5 AM PDT Wednesday for PZZ253-273.
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