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. --632FXUS66 KPQR 181816 AABAFDPQRArea Forecast Discussion...UPDATEDNational Weather Service Portland OR1116 AM PDT Sun Aug 18 2024&&.SYNOPSIS...Showers will linger across the area this morning,primarily west of I-5 as an offshore low pressure system movesnorth along the coast. Can`t rule out a few rumbles of thunderwith this activity. Drier and sunnier conditions expected thisafternoon with highs in the 70s. Benign onshore flow thenexpected to continue through much of the next week, withoccasional light shower activity and inland highs remaining inthe 70s.&&.DISCUSSION...Considerably quieter weather prevails across thearea early this Sunday morning as the heavier shower andthunderstorm activity associated with a potent shortwave troughhas shifted well north into Washington and British Columbia.Partial clearing in the wake of this activity has allowed patchyand locally dense fog to form across much of the area given theabundant low level moisture in place from yesterday and lastevening`s rainfall.Meanwhile, a deep upper level low is still located justoffshore of the north Oregon Coast, and this will be thecatalyst for lingering shower activity across parts of the areathis morning. Already seeing some weak radar echos starting tofill back in across the southern half of the area as of 3 AMSunday, and expect this trend to continue later into the morningas another impulse rotating around the large scale troughtracks northward across the region. The bulk of this morning`sshower activity will be concentrated west of I-5, though a fewshowers could drift farther east over the Willamette Valley attimes as well. Can`t rule out a few rumbles of thunder with thisactivity, but certainly nothing like yesterday in terms ofcoverage or intensity given much more meager moisture, lift, andinstability in place today. All told, additional rainfallamounts should be limited to a tenth of an inch or less todaywith locally higher amounts in thunderstorms. Expect anylingering showers to be confined to northern coastal areas byearly afternoon as the upper low continues to drift northwardoff the Washington Coast. This will yield dry conditions andmostly sunny skies across most of the area this afternoon, withhighs in the upper 70s in the inland valleys.Medium to long range guidance continues to point to fairlybenign, low impact weather for the week ahead as the PacificNorthwest remains under the influence of upper level troughingand onshore flow through next weekend. Generally expect inlandhighs in the mid to upper 70s each day, with spotty showeractivity lingering over the area at times in proximity to thetrough. The large scale trough looks to be reinforced by anotherupper low dropping south along the BC coast Wednesday nightinto Thursday, which could bring increased shower coverage andrenewed thunderstorm chances mid to late week. Ensemble anddeterministic guidance then show fairly good agreement that thetrough will eventually evolve into a cutoff low centered overnorthern California by next weekend. /CB&&.AVIATION...
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Satellite imagery and terminal observations as of18z Sun remain a mix of IFR/MVFR/VFR cigs/vis as a post-frontalregime sets up across the region. Scattered, light showers arepossible along the coast and coast range into early thisafternoon. Skies will gradually clear to VFR this afternoon.Expect south/southwest winds around 10 kts, with gusts up to 25kt along the coast and 20 kt in the Willamette Valley. After 00zMon, winds weaken below 10 kt. Could also see a return of marinestratus along the coast Sunday evening as conditions cool andmoisten.PDX AND APPROACHES...Predominately VFR thresholds through the TAFperiod. Southeast winds will strengthen and turn more southerlythis afternoon, along with gusts up to 20 kt. -Batz/Alviz
-- End Changed Discussion --&&.MARINE...Low pressure over the NE Pacific will bring marginalsmall craft conditions to the waters between Cape Shoalwater, WAand Cape Foulweather, OR. Expect southerly winds 15-20 kt withgusts up to 25 kt. Therefore, a Small Craft Advisory has beenissued for those marine zones including the Columbia River Barfrom 11 AM to 8 PM today. In addition, a second Small CraftAdvisory was issued for the Columbia River Bar for early Mondaymorning as a very strong ebb is expected. Seas will remainaround 3 to 5 feet through the end of the week. -Alviz&&.PQR WATCHES/WARNINGS/ADVISORIES...
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OR...None.WA...None.PZ...Small Craft Advisory until 8 PM PDT this evening for PZZ210- 251>253-271>273. Small Craft Advisory from 3 AM to 8 AM PDT Monday for PZZ210.
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