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. --382FXUS66 KPQR 070351 AAAAFDPQRArea Forecast Discussion...UPDATEDNational Weather Service Portland OR850 PM PDT Thu Jun 6 2024Updated Aviation and Marine Discussions.SYNOPSIS...
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Going into the weekend high pressure likelymaintains mostly dry conditions and above normal temperaturesalthough once we get beyond Friday high temperatures will begina decline going forward, albeit very gradually Sunday onward.Late Saturday into Sunday expect increasing cloud cover due to aweak upper-level trough, but little to no precipitation expectedoutside of shower activity near the Cascade crests and thepotential for morning drizzle along the coast. Back to weakridging/zonal flow aloft Monday through Wednesday noappreciable weather impacts. Some guidance shows a breakdown inthe upper-level pattern via a upper trough pushing into thePacific Northwest from the Gulf of Alaska around Thursday ofnext week ushering in chances (15-40%) for light precipitationhowever exact timing/amounts at this point are unclear..SHORT TERM...Today through Sunday...Expect high pressure topersist over the Pacific Northwest through the end of the workweek and most of Saturday maintaining dry conditions and warmtemperatures. The axis of the upper-level ridge shifts overheadon Friday, subsequently at the same time a subtle shortwavetraverses overhead(well get to that in a minute), but theprimary impact of this overall pattern will be afternoon hightemperatures 15 to 20 degrees above normal for the inlandvalleys away from the marine influence from the coast. Thelatest NBM guidance suggests a high degree of confidence(70-90%) in temperatures meeting or exceeding at least 85degrees across the Willamette Valley, SW Washington, and in theCascade valleys come Friday afternoon. However given a slightoffshore component to the surface-850mb flow and clear skiesthinking 90 degrees is within the realm of possibility for thePortland/Vancouver metro and base of the Cascade foothills evenif the NBM probabilities to meet/exceed 90 are only 30-50%.These locations will have a moderate heat risk - this level ofheat affects most individuals sensitive to heat, especiallythose without effective cooling and/or adequate hydration. Keepthis in mind if you plan on spending any extended period of timeoutdoors.Another feature worth watching on Friday, specifically late inthe day, is a weak/subtle upper-level shortwave traversing intoOregon accompanied by a plume of mid-level moisture situatedaround 700-600mb. With ample daytime heating just before thearrival of this feature and models like the NAM/GFS showingaround 300-500j/kg of MUCAPE in an elevated layer between700-300mb the environment is marginal for the development ofisolate mid-level based convection along the crests of theCascades along far eastern Lane County late Fridayafternoon/evening. The latest HREF does show a couple membersinitiating weak thunderstorms in this region of mid-levelmoisture/insatiably so have added a slight chance(10-15%) forthunderstorms along the Lane/Deschutes county line, althoughchances for isolated convection appear more favorable further SEwhere the mid-level moisture layer is more robust. All thatbeing said, both the HRRR, 4KNAM, and UW-WRF are fairly bearishwithin the greater CAM ensemble space during this period alongthe Cascades into central Oregon so confidence in the set-up israther low likely owing to a rather deep dry layer just abovethe moisture at 700-600mb working to entrain dry air into risingparcels - this would inhibit the formation of anythunderstorms. All in all, dont be taken by complete surprisedif an isolated T-storm does indeed develop along theLane/Deschutes county line Friday but the window for anyactivity will be rather brief (4-8pm), if anything actually doesmaterialize.Friday night, the upper level ridge begins to progress eastwardas a weaken upper-level trough approaches the Pacific Northwest.This will bring more southwesterly flow aloft as well asincreasing mid to high level cloud cover Saturday. Since our airmass will be so dry when this shortwave moves in, it`s unlikelythat we`ll see much precipitation outside of a 15-30% chance forshowers along the Cascades late Saturday night through Sunday.The added westerly flow and cloud cover will help to lowertemperatures through the weekend with high temperatures likelyin the upper 70s to low 80s for the inland Valleys on Saturday,dropping into the mid 70s to near 80 on Sunday - still pleasantoverall. Low temperatures continue to bottom out in the 50sproviding some overnight cooling. -Schuldt.LONG TERM...Sunday Night through Thursday Going forward intoearly next week most WPC ensemble clusters are in generalagreement of maintaining low amplitude high pressure with above-normal 500 mb heights over the Pacific Northwest throughWednesday. However, the clusters still differ on the precisemagnitude and placement of the ridging, more apparent beginningon Wednesday when ensemble guidance shows an upper trough nearthe Gulf of Alaska beginning to show signs of progressingsouthward towards British Columbia and potentially the PacificNorthwest. Depending on how far south this trough ends up atthis point, this would influence the strength of high pressureover us and thus how warm we end up getting around the middle ofnext week. Come Thursday nearly 35-40% of the total ensemblemembers begin to bring the aforementioned broad upper-levelthrough into the region thus increasing chances forprecipitation should this scenario pan out. The remaining 60-65%of ensemble keep the influence of the low amplitude ridgeoverhead to varying degrees, shunting the trough to our north.Generally speaking, the pattern favors a continuation of abovenormal temperatures through the extended, but with lessconfidence on where high temperatures will ultimately landaround the middle of next week. -Schuldt/Alvis
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High pressure will remain in control across theregion through the weekend. This will result in warm and dryconditions with widespread VFR under primarily clear skies.North/northwest winds, generally 5-10 kt inland and up to 15kt along the coast, with wind gusts up to 25 kt along the coastand gusts up to 20 kt within the Willamette Valley. Inland windswill become light and variable after 06Z Friday. Coastal windswill remain elevated through the overnight hours, but gustsexpected to fall below 15 kt around 15Z Friday. Gusty surfaceconditions return across the airspace around 20Z Friday with gustsalong the coast up to 20 kt and gusts inland up to 15 kt.PDX AND APPROACHES...VFR with generally clear skies. Northerlywinds with gusts up to 20 kt through 06Z Friday. Afterwards,winds become light and variable. /42
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High pressure over the region will lead to clear skiesand fairly persistent north/northwest winds through the weekend.Gusts up to 25 knots across all waters through early Fridaymorning. Conditions will slowly subside from north to souththrough Friday morning. Could see some isolated gusts up to 25 ktwithin zones PZZ272, PZZ252, PZZ273 and PZZ253 through Fridayafternoon. Seas remain steep around 7 to 9 ft at 10-12 seconds.Therefore, have adjusted the current Small Craft Advisories toreflect the newest data from the forecast models.Conditions will begin to ease on Saturday as a very weak frontnears the waters. This front appears to have limited impact, butcannot rule out some isolated gustier conditions. Seas will lowerto around 5 to 7 ft at 12 seconds. /42-Batz/Muessle
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OR...None.WA...None.PZ...Small Craft Advisory from 4 AM to 8 AM PDT Friday for PZZ210. Small Craft Advisory until 1 AM PDT Friday for PZZ251-271. Small Craft Advisory until 6 AM PDT Friday for PZZ252-253-272- 273.
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