Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
304 FXUS66 KPQR 180317 AFDPQR Area Forecast Discussion National Weather Service Portland OR 814 PM PDT Mon Jun 17 2024 .SYNOPSIS...Showers decrease this evening as low pressure exits the region. Drier conditions return tomorrow, with winds turning more northerly. Wednesday to Friday, conditions become much warmer and drier as light easterly winds downslope from the Cascades. Conditions begin to cool down and become more moist late this weekend. && .SHORT TERM...Now through Wednesday night...Radar imagery as of 800 PM PDT depicts lingering shower activity across portions of northwest OR and southwest WA, mainly over the Cascade foothills, Cascades, and northern Willamette Valley. Based on CAM guidance, expect lingering showers to decrease through this evening as low pressure exits the area. Westerly winds will also gradually ease. Overnight lows will be pretty chilly for mid to late June, forecast in the 40s for interior valleys and 30s for high terrain. Tomorrow (Tuesday), expect warmer weather as 500 mb heights increase. Temps will be near seasonal normals, with highs forecast in the low to mid 70s for interior valleys and 60s along the coast. Winds will also turn more northerly, bringing drier air to the region. Wednesday, we`ll start to see a thermal trough developing east of the Cascades over central Oregon. This will lead to light (less than 10 mph) easterly winds downsloping from the Cascades, but most Willamette Valley winds will be northerly. As a result, expect much warmer conditions in the Willamette Valley and lower relative humidities (around 30%). Wednesday afternoon highs are forecast to climb into the mid 80s for interior valleys. NBM probabilities for temps greater than 85 degrees for interior valleys are currently around 60-80%. Meanwhile, the coast will still remain mild with higher humidity and temps in the 60s as they maintain a slight onshore component to the wind. -Alviz && .LONG TERM...Thursday through Monday...High pressure increases through the remainder of the weekend, though it is a bit more convoluted as there is not good vertical continuity. While high pressure is forming at the surface, a troughing pattern is developing in the mid levels. However, looking at the jet stream (around 35,000 ft) there is a very clear ridging pattern. Because of this overall messy pattern, confidence is a bit lower than desired for the long term forecast. In a similar realm to locations in the east, we will be warming up quite a bit but not nearly as hot. Ultimately, temperatures will be just slightly above normal. They challenge remains "just how hot will it be?". Thursday will be the first day of considerable warming with temperatures forecast in the mid to upper 80s inland, and cooler along the coast. Friday is slated to be the hottest day of the week with the NBM showing temperatures into the 90s around Portland. Now, the NBM has been quite variable increasing temperatures day by day. Specifically looking at the greater Portland/Vancouver-Metro area, the box and whisker plots for temperatures has narrowed which generally would coincide with more confidence in the forecast. However, looking at the other long-term ensembles, it is a bit less clear. Maximum temperatures around Troutdale on Friday have the highest probability to be around 85-90 Degrees F, with only an 10% chance of exceeding 90 degrees F. The NBM deterministic is putting Troutdale right at and slightly above 90 degrees. Given the variability have decided to let the NBM ride until we get a few more runs to hopefully narrow in on a better pattern. The other component to feature with this is a weak north to easterly wind throughout most of the forecast area. This will enhance warming, and drying with humidity plummeting ranging from 20-30% with the driest conditions along the Cascades and the Columbia River Gorge. The east wind could increase downslope and warming which may be contributing to the higher temperatures. Saturday will be the transitional day as a long wave trough begins to drop down from the Gulf of Alaska. 500 mb heights are lowering to the north, and the bulk of the low aloft will transcend along the WA/Canadian border. This system will usher in cooler air dropping temperatures on Sunday. Precipitation is possible with southwesterly flow, but accumulations will be minimal and not impactful. -Muessle && .AVIATION...Onshore flow will continue overnight, though will gradually weaken. But, will maintain plenty of clouds along the coast as well as inland, especially against the mountains with bit of upslope flow. Generally, am expecting mostly VFR with CIGS 3500 to 5000 ft overnight, but will have some patchy lower MVFR along the coast and inland through the Cowlitz lowlands and against the south Washington Cascades overnight. Low level flow will turn bit more northerly to south of a Newport to Albany line later tonight, with clouds clearing to the south. That clearing will gradually work its way northward, with most all areas in VFR with few to scattered clouds by 20Z. PDX AND APPROACHES...VFR tonight, with broken CIGS around 5000 to 6000 ft. Will maintain bit more open sky to west and south of Portland this evening, but think that will fill back over as the clouds on the west slopes of the Cascades backbuild over the region. While there is a small chance (25-35%) of higher end MVFR CIGS between 10Z and 15Z, thinking these will remain farther to the north over Clark County, keeping PDX mostly VFR into Tue am. Will trend 06Z TAF that direction. Clouds break up 18Z to 21Z, with VFR under mostly clear skies afterwards. && .MARINE...High pressure offshore is expected to persist through the week. Northwest winds 10-15 kt across coastal waters today becoming northerly on Tuesday. North winds begin to increase later Tuesday afternoon as a thermal trough strengthens from northern CA into southern OR, so have issued a Small Craft Advisory for PZZ 253, 273, but may need to be extended further north. Expect will see periods of winds gusting up to 25 kt through Friday during the late afternoon and evenings. Seas around 4 to 6 feet will generally be wind driven through the week. /mh /DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Small Craft Advisory from 2 PM Tuesday to 4 AM PDT Wednesday for PZZ253-273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland www.twitter.com/NWSPortland