Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
431 FXUS66 KPQR 102243 AFDPQR Area Forecast Discussion National Weather Service Portland OR 343 PM PDT Mon Jun 10 2024 .SYNOPSIS...A warm and sunny June afternoon for SW Washington and NW Oregon as high pressure dominates the region today. The high pressure will weaken and shift eastward tonight, allowing a decaying cold front to brush the forecast area Tuesday. Precipitation will be minimal, though there will likely be areas of drizzle along the coast. Otherwise, a deeper marine layer and strong onshore flow will lead to cooler temperatures Tuesday into Wednesday. High pressure brings a brief warmup Thursday, but below normal temperatures appear likely for the weekend as an upper trough moves into the Pac NW with clouds and a few showers. && .SHORT TERM...Now through Thursday...Quiet weather across NW Oregon and SW Washington this afternoon under high pressure. After a cool start with many outlying areas in the 40s and lower 50s, temps climbed rapidly during the midday hours and most of the forecast area is 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 in the Coast Range; for example, the 2 PM temperature at Tidewater RAWS was 73 deg F - versus 51 deg F at the same time Sunday. This is likely due to a more northerly component to the low-level flow and a shallower marine layer, both acting to limit the influence of the cooler marine air. A vigorous upper level trough along 140W is causing low pressure to develop near 46N/133W as of 3 PM; this low will track NE eventually pushing a weak cold front toward the Pac NW coast. The upper trough and approaching front will cause the marine layer to rapidly deepen late tonight; eventually deepening it enough to produce areas of drizzle along the coast and in our coastal ranges. It does not appear the moist layer will be deep enough for precipitation to reach the Willamette Valley, but locations such as Battle Ground near the S WA Cascade foothills may still see some occasional drizzle. The cold front actually moves onshore and across the Willamette Valley midday or early afternoon Tuesday, so there will be at least some degree of cloudiness for most of the day. One exception to this may be the Eugene metro, where the front may be slow enough to arrive such that the first half of the day has plenty of sunshine and temps climb to the 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 a cool night by June standards Tuesday night throughout the forecast area. With dewpoints expected to fall deep into the 30s (possibly even the 20s) and winds calming down overnight, it would not be surprising if some of our coolest outlying valley locations such as Timber Jct dip into the upper 30s Wednesday morning. Frost is highly unlikely, but it will be chilly for the season. The cool start to the day Wednesday will hold back temps a bit, just like today, but the air mass will be warming up so afternoon temps should end up seasonable. High pressure will persist through Thursday, leading to another cool night Wednesday night, but probably not quite as cold as Tuesday night. As the air mass continues to warm Thursday, it appears likely Thursday afternoon will be a few degrees warmer than mid-June normals. Based on NBM probabilistic guidance, it appears there is a 40-70% 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 to shift east of the forecast area on Friday as another trough near the Gulf of Alaska dips southward toward the Pacific Northwest. This will lead to a cooling trend and return of widespread low PoPs. Saturday, most ensemble members agree on troughing entering the region with below-average 500 mb heights. If this scenario pans out, then we would see increasing chances for widespread precipitation and below average temperatures. For now, the NBM`s 20-50% chance of PoPs across northwest Oregon and southwest Washington at the end of the week look reasonable. Sunday, most ensemble members (85%) continue to show troughing, but are uncertain of the exact axis location and magnitude. Meanwhile, the other 10% of members show zonal flow or weak ridging returning over us, which would lead to a warm-up back to more seasonable mid-June temperatures. -Alviz/Weagle && .AVIATION...Current satellite shows clear skies and VFR conditions across the western Oregon and SW Washington this afternoon. Overnight into Tuesday morning a very weak frontal boundary will move into the area starting with high clouds streaming into the region, at least initially. Expect the marine layer and at least MVFR CIGS to re-develop at the coast later this evening and overnight as well with chances (around 30-40%) for IFR stratus and light rain and/or drizzle near KAST after 10-12z. Inland sites likely stay VFR through Tuesday morning, but will still see cloud cover increase and CIGS lower. Probabilities for MVFR CIGS then increase to 20-40% for inland sites after ~20z Tuesday. PDX AND APPROACHES...Generally VFR cigs/vis with northwesterly flow through the day. While stratus will reform Tuesday morning, there is only a 20-30% chance for MVFR CIGs towards the end of the TAF period after 16-17z Tuesday, increasing to 30-40% after 20z Tuesday. -Schuldt && .MARINE...High pressure will begin to progress to our east this evening and overnight ahead of a weak weather disturbance approaching the Pacific Northwest. On Tuesday, a weak frontal boundary passes over the waters but will likely not be impactful as far as wind is concerned (at least initially), decaying as it reaches the shore. That said, an accompanying westerly swell arriving on Tuesday will push seas to 10-13 feet at 11-13 seconds leading to Small Craft Advisory conditions. Following this trough northerly winds will also increase Tuesday night into Wednesday as another area of high pressure redevelops over the waters - gusts between 20-30 knots likely. Come Wednesday evening/night when winds peak the NBM projects a 70-90% chance for Small Craft Advisory level wind gusts (>21 knots) with similar probabilities persisting through Thursday. From there, another trough is anticipated to move into the region late week into the weekend, although confidence is low in the exact impact at this time. -Schuldt && .PQR WATCHES/WARNINGS/ADVISORIES... 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. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland