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. --513FXUS66 KPQR 071019AFDPQRArea Forecast DiscussionNational Weather Service Portland OR319 AM PDT Fri Jun 7 2024.SYNOPSIS...
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High pressure will maintain above-normal temps andmostly dry conditions through early next week. Today will be thewarmest day of the week. A weak shortwave trough Saturday willbring increasing mid to high level cloud cover and a 15-30%chance for showers in the Cascades. The Lane County Cascadeshave a slight chance for thunderstorms Saturday afternoon/night.Onshore flow will keep temps moderated along the coast.
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Today through Sunday...A high pressure ridge overthe Pacific Northwest will reach it`s maximum amplitude today,leading to dry weather, sunshine, and the warmest temperaturesof the week. Afternoon highs today are forecast in the mid toupper 80s for interior valleys, which are about 15 degrees abovenormal for this time of year. NBM probabilities of exceeding 90degrees has fallen to around 15-30% for the Portland Metro toUpper Hood River Valley. Meanwhile, onshore flow will help keeptemps moderated along the coast, with highs in the upper 60s tolow 70s. Keep in mind that even though the air will be warmtomorrow, rivers and lakes will still be very cold! Use extraprecaution if swimming in local bodies of water, as cold watercan lead to hypothermia or cold water shock.Overnight, there will be decent relief from the warm temps asSaturday morning lows are forecast in the 50s across the area.The aforementioned ridge will also begin to progress eastwardas a weak upper-level shortwave trough approaches the region.This shortwave will bring more moist, southwesterly flow aloftas well as increasing mid to high level cloud cover Saturday.Saturday high temps for inland valleys will still be warm andaround 10 degrees above normal, but likely a few degrees coolerthan the previous day due to increased cloud cover.Precipitation with this shortwave trough is also unlikely sinceour pre-existing air mass will dry. However, an exception wouldbe the Cascades, where surface heating and upslope flow couldsupport a 15-30% chance for showers Saturday afternoon-night.HREF does show MUCAPE values of 250-500 J/kg Saturday afternoonover the Cascades. And looking at SREF and HiResW-ARW soundings,the instability is mainly above 10,000 ft. Combine that withincreased mid-level moisture, we could see an elevatedthunderstorm or two pop up along the Cascade crest. However,with the westerly component to the wind aloft, any showers orthunderstorms that do develop on Saturday would likely getpushed into central and eastern Oregon. Went ahead and kept the15-20% chance of thunderstorms given by NBM for the Lane CountyCascades.The slight cooling trend continues on Sunday as the upper-levelshortwave trough moves over us and exits the Pacific Northwest.We`ll have onshore flow which will help with cooling temps abit. However, temperatures are still forecast above-normal forinland valleys, topping out in the upper 70s to low 80s. NBMsuggests a 40-50% chance that inland valleys exceed 80 degreeson Sunday. Overall, pleasant summer-like conditions through theweekend. -Alviz
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Sunday Night through Thursday...To summarize, theweather pattern in the early part of the extended forecast favorsa continuation of above-normal temperatures through Tuesday.However, uncertainty comes mid-week with how an upper troughnear the Gulf of Alaska will influence the weather in thePacific Northwest:Based on WPC cluster analyses, a low amplitude ridge will re-build behind the shortwave trough Sunday night into Monday. Theclusters are also in agreement of above-normal 500 mb heightsthrough Tuesday. This will maintain warm temperatures going intoearly next week. The latest NBM suggests a 40-50% chance ofinland valleys exceeding 80 degrees Monday and Tuesday. However,all of the clusters show the ridge beginning to flatten onTuesday as an upper trough near the Gulf of Alaska progressesinto British Columbia. By Wednesday, ensembles are showing morezonal flow, which would lead to further cooling of temperatures.More uncertainty comes on Thursday with the upper levelpattern. About 50% of ensemble members show the upper troughdipping southward toward the Pacific Northwest, increasingsouthwesterly flow aloft. If this pans out, then we could seeeven cooler temperatures and potential for precipitation.Meanwhile, the other 50% of members show either zonal flow or abuilding ridge. If these scenarios pan out, then we wouldmaintain relatively warmer and drier conditions. -Alviz
-- End Changed Discussion --&&.AVIATION...
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High pressure persists through 12Z Saturday leading toVFR CIGs and VIS. Onshore flow through the day with a northerlywind in the afternoon. Misty conditions along the coast untilafter sunrise around 15Z. Warm conditions are expected today,especially from KPDX south to KEUG within the Willamette Valley,and around K4S2. It is possible that thermals will be presentalong runways. Winds will be northwesterly up to 3000 ft AGL up to20 kt.PDX AND APPROACHES...VFR with no concerns. Increased winds in theafternoon. Thermal eddies possible in the afternoon along runwaysdue to elevated heating. -Muessle
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High pressure remains through Saturday morning.Northwesterly flow will dominate with gusty conditions up to 25kt. Small craft advisory has been extended from Cape Falconsouthward through the evening as gusts will remain around 25 kt.In the northern waters, those winds and seas will ease sooner.Some models are suggesting a brief period of gusts to 25 kt in thesouthern portions of PZZ271/251 from 1400-1900. Given that theyare going to be localized and isolated, have not continued theadvisory for the northern waters.Seas will be around 7-9 ft at 13 seconds until Saturday when theyease to less than 7 ft. This will be short-lived though because aweak cold front arrives on Sunday causing winds to increase againfrom the west. The westerly winds will combine with the westerlybackground swell causing significant wave heights to rise near 10ft. -Muessle
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OR...None.WA...None.PZ...Small Craft Advisory until 8 AM PDT this morning for PZZ210. Small Craft Advisory until 6 AM PDT early this morning for PZZ251-271. Small Craft Advisory until 11 PM PDT this evening for PZZ252-253- 272-273.
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