National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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431FXUS66 KPQR 102243AFDPQRArea Forecast DiscussionNational Weather Service Portland OR343 PM PDT Mon Jun 10 2024.SYNOPSIS...

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A warm and sunny June afternoon for SW Washington and NWOregon as high pressure dominates the region today. The high pressurewill weaken and shift eastward tonight, allowing a decaying coldfront to brush the forecast area Tuesday. Precipitation will beminimal, though there will likely be areas of drizzle along thecoast. Otherwise, a deeper marine layer and strong onshore flow willlead to cooler temperatures Tuesday into Wednesday. High pressurebrings a brief warmup Thursday, but below normal temperatures appearlikely for the weekend as an upper trough moves into the Pac NW withclouds and a few showers.

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Now through Thursday...Quiet weather across NW Oregonand SW Washington this afternoon under high pressure. After a coolstart with many outlying areas in the 40s and lower 50s, tempsclimbed rapidly during the midday hours and most of the forecast areais now as warm or warmer than they were at the same time yesterday.The warming trend today has been most notable along the coast and inthe Coast Range; for example, the 2 PM temperature at Tidewater RAWSwas 73 deg F - versus 51 deg F at the same time Sunday. This islikely due to a more northerly component to the low-level flow and ashallower marine layer, both acting to limit the influence of thecooler marine air.A vigorous upper level trough along 140W is causing low pressure todevelop near 46N/133W as of 3 PM; this low will track NE eventuallypushing a weak cold front toward the Pac NW coast. The upper troughand approaching front will cause the marine layer to rapidly deepenlate tonight; eventually deepening it enough to produce areas ofdrizzle along the coast and in our coastal ranges. It does not appearthe moist layer will be deep enough for precipitation to reach theWillamette Valley, but locations such as Battle Ground near the S WACascade foothills may still see some occasional drizzle. The coldfront actually moves onshore and across the Willamette Valley middayor early afternoon Tuesday, so there will be at least some degree ofcloudiness for most of the day. One exception to this may be theEugene metro, where the front may be slow enough to arrive such thatthe first half of the day has plenty of sunshine and temps climb tothe mid 70s before the front arrives Tuesday afternoon.Strong high pressure will build in behind Tuesday`s frontal system,first leading to strong west winds through the Columbia Gorge, then acool night by June standards Tuesday night throughout the forecastarea. With dewpoints expected to fall deep into the 30s (possiblyeven the 20s) and winds calming down overnight, it would not besurprising if some of our coolest outlying valley locations such asTimber Jct dip into the upper 30s Wednesday morning. Frost is highlyunlikely, but it will be chilly for the season. The cool start to theday Wednesday will hold back temps a bit, just like today, but theair mass will be warming up so afternoon temps should end upseasonable.High pressure will persist through Thursday, leading to another coolnight Wednesday night, but probably not quite as cold as Tuesdaynight. As the air mass continues to warm Thursday, it appears likelyThursday afternoon will be a few degrees warmer than mid-Junenormals. Based on NBM probabilistic guidance, it appears there is a40-70% chance of the PDX metro reaching 80 deg F Thursday afternoon,while chances for the same in Eugene are closer to 20%. Weagle.LONG TERM...Friday through Monday...The upper ridge begins toshift east of the forecast area on Friday as another trough near theGulf of Alaska dips southward toward the Pacific Northwest. This willlead to a cooling trend and return of widespread low PoPs. Saturday,most ensemble members agree on troughing entering the region withbelow-average 500 mb heights. If this scenario pans out, then wewould see increasing chances for widespread precipitation and belowaverage temperatures. For now, the NBM`s 20-50% chance of PoPs acrossnorthwest Oregon and southwest Washington at the end of the week lookreasonable. Sunday, most ensemble members (85%) continue to showtroughing, but are uncertain of the exact axis location andmagnitude. Meanwhile, the other 10% of members show zonal flow orweak ridging returning over us, which would lead to a warm-up back tomore seasonable mid-June temperatures. -Alviz/Weagle

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Current satellite shows clear skies and VFR conditionsacross the western Oregon and SW Washington this afternoon.Overnight into Tuesday morning a very weak frontal boundary willmove into the area starting with high clouds streaming into theregion, at least initially. Expect the marine layer and at leastMVFR CIGS to re-develop at the coast later this evening andovernight as well with chances (around 30-40%) for IFR stratus andlight rain and/or drizzle near KAST after 10-12z. Inland sites likelystay VFR through Tuesday morning, but will still see cloud coverincrease and CIGS lower. Probabilities for MVFR CIGS thenincrease to 20-40% for inland sites after ~20z Tuesday.PDX AND APPROACHES...Generally VFR cigs/vis with northwesterlyflow through the day. While stratus will reform Tuesday morning,there is only a 20-30% chance for MVFR CIGs towards the end of theTAF period after 16-17z Tuesday, increasing to 30-40% after 20zTuesday. -Schuldt

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High pressure will begin to progress to our east thisevening and overnight ahead of a weak weather disturbanceapproaching the Pacific Northwest. On Tuesday, a weak frontalboundary passes over the waters but will likely not be impactfulas far as wind is concerned (at least initially), decaying as itreaches the shore. That said, an accompanying westerly swellarriving on Tuesday will push seas to 10-13 feet at 11-13 secondsleading to Small Craft Advisory conditions. Following this troughnortherly winds will also increase Tuesday night into Wednesday asanother area of high pressure redevelops over the waters - gustsbetween 20-30 knots likely. Come Wednesday evening/night whenwinds peak the NBM projects a 70-90% chance for Small CraftAdvisory level wind gusts (>21 knots) with similar probabilitiespersisting through Thursday. From there, another trough isanticipated to move into the region late week into the weekend,although confidence is low in the exact impact at this time.-Schuldt

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OR...None.WA...None.PZ...Small Craft Advisory from 5 PM Tuesday to 5 AM PDT Wednesday for PZZ210. Small Craft Advisory from 11 AM Tuesday to 11 PM PDT Thursday for PZZ251-252-272. Small Craft Advisory from 5 PM Tuesday to 11 PM PDT Thursday for PZZ253-273. Small Craft Advisory from 8 AM Tuesday to 11 PM PDT Thursday for PZZ271.

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