Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
481 FXUS66 KPQR 231010 AFDPQR Area Forecast Discussion National Weather Service Portland OR 309 AM PDT Sun Jun 23 2024 .SYNOPSIS...Cooler and cloudier on Sunday with drizzle or light rain at the coast, western slopes of the Coast Range, Cascades and eastern Portland/Vancouver metro. Dry on Monday with seasonable temperatures. A transient shortwave ridge will bring a brief warmup on Tuesday before an upper level trough brings relatively cooler temperatures Wednesday through Thursday along with periodic chances for rain showers. Trending slightly warmer again next weekend. && .DISCUSSION...SUNDAY THROUGH SATURDAY NIGHT...Satellite imagery from early Sunday morning depicted mostly cloudy skies across northwest OR and southwest WA due to a marine push. In addition to the extensive cloud cover, areas of drizzle were being observed at the coast and portions of the Cascade foothills. This trend will continue through Sunday morning, with light drizzle potentially impacting the Camas/Troutdale area into the western Columbia River Gorge as well. Otherwise expect a mix of sun and clouds Sunday afternoon with high temperatures in the low to mid 70s across the lowlands, except upper 50s to mid 60s at the coast. Dry conditions will prevail across the region on Monday with plenty of sunshine and seasonable temperatures. Overall Monday looks to be a great day for outdoor activities. Heating up again on Tuesday as a shortwave ridge moves inland, however models and their ensembles continue to suggest this ridge will be fast-moving as an upper level trough over the northeast Pacific approaches the Pacific Northwest. With this pattern in place, Tuesday will be the warmest day of the week with highs temps well into the 80s from Vancouver to Eugene, Portland to Hood River, and in the Cascade valleys. Cannot completely rule out high temps in the lower 90s in these areas as the probability for high temps of 90 degrees or warmer is around 5-15%. Despite the warmer temps on Tuesday, the aforementioned upper level trough will bring a quick return to cooler temperatures for Wednesday and Thursday with high temps in the low to mid 70s and 60s at the coast. This trough will also bring increasing chances for rain showers. NBM 6-hr PoPs have increased a bit during that time but the exact timing remains uncertain. Nevertheless, confidence is fairly high that most locations in southwest WA and far northwest OR will see at least some measurable rain on Wednesday and/or Thursday as nearly every ensemble member from the GEFS/EPS/CMC show QPF at PDX, albeit at different times. To help account for these timing differences, it is likely better to message 24-hour PoPs rather than 6-hour PoPs to ensure the probability does not appear misleadingly low. For example, NBM 6-hr PoPs range between 15-60% while NBM 24-hr PoPs range between 25-90% (highest over southwest WA and lowest in the Eugene area). After this trough moves through the region, models and their ensembles are generally trending a bit warmer and drier Friday into next weekend as weak ridging develops. Only one cluster on WPC`s cluster analysis is showing a trough during that time, but this cluster only makes up 13% of the total ensemble space and is mainly driven by the cooler GEFS solution. Regardless of the outcome, there are no signs of extreme heat or any impactful weather next weekend. Enjoy!-TK && .AVIATION...Post frontal onshore flow continues with high pressure offshore. Widespread stratocumulus field extends from the coast to well offshore, as well as filling in over western Oregon and Washington. MVFR cigs prevail across the area as of 10Z Sun. For inland areas chances for MVFR remain high (60-90% chance) then begin to decrease after 15Z Sun with VFR more likely after 19Z Sun. Coastal areas too will see improvement through the day. Westerly winds north of about KTMK will keep that area rather cloudy with cigs in the high MVFR to low VFR range. But northerly wind developing toward KONP indicates better chance for clouds to break up more with VFR after 20Z Sun. PDX AND APPROACHES...MVFR chances remain high (70-90%) in the area through 15Z Sun then chances begin to decrease. VFR is expected after 19Z Sun with less than 20% chance for MVFR. Winds remain light northwest in the morning, increasing to around 10 kt for later in the afternoon and evening. /mh && .MARINE...Low pressure around 1010 mb near Haida Gwaii Sun morning with high pressure to the southwest. The resulting wind field suggests a weak dynamic fetch which could generate seas higher than forecast. But as of 3 am Sunday wave models are within 1 ft of buoy observations. Though the coastal waters will see westerly swell build this afternoon will be in the 7 to 9 ft range. Otherwise, high pressure will expand across the waters through Monday while thermal low pressure strengthens over the Sacramento Valley and near the OR/CA border. This will lead to moderate N-NW flow through Tues, with about a 20-40% chance of wind gusts exceeding SCA criteria of 21 kt Monday afternoon. This pattern weakens the winds by mid-week as another low pressure system over the northeast Pacific nudges closer to the Pacific Northwest. /mh -Weagle && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland