


Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
998 FXUS66 KPQR 182200 AFDPQR Area Forecast Discussion National Weather Service Portland OR 300 PM PDT Fri Jul 18 2025 .SYNOPSIS...Strengthening onshore flow will bring continued cooling through the weekend with temperatures falling before normal to begin the next workweek. An upper low passing overhead Sunday night into Monday may bring the best chances for rain so far this month, although odds for accumulating precipitation remain fairly low. Forecast confidence decreases midweek, although a return to warmer temperatures is most likely. && .SHORT TERM...Now through Sunday...Another upper-level shortwave passing over or just north of the region this afternoon and evening will usher in intensified onshore flow, continuing the cooling trend through the weekend. Mid-level temperatures around 15C at 850 hPa today will fall to 10-11C by Sunday afternoon, pushing surface temperatures below seasonal normals, with afternoon highs falling to the 60s along the coast and in terrain, and mid 70s to low 80s along the I-5/I-84 corridors. The stronger onshore push will also favor increased low cloud cover, especially along the coast and into Coast Range gaps, including up the Columbia River into the Portland/Vancouver metro. Coastal mist and fog are also most likely Sunday morning reaching into west-facing Coast Range valleys. West to northwest winds will also strengthen modestly, with gusts as high as 30-35 mph through the Columbia Gorge each afternoon. -Picard .LONG TERM...Sunday Night through Friday...By Sunday night into Monday, there is increasing consensus that a vigorous upper shortwave will dive southward over the Haida Gwaii and Vancouver Island, resulting in elongated upper troughing or even a cutoff low centered developing over the Pacific NW. While this wave may support light rain reaching into the region to start the workweek, chances remain fairly low, only 15-25% along the coast and in the Coast Range, and slightly lower in the Cascades and foothills. It`s worth noting that an increased number of global ensemble members are showing accumulating rain as well as anomalously high values of precipitable water, generally 1-1.25" across the forecast area, which would be above the 90th climatological percentile of KSLE sounding observations. With light mean cloud-level winds, around 5 kt, slow-moving convective showers which could wring out a true wetting rain in some areas cannot be ruled out. Numerical guidance then diverges toward the middle of the week as the evolution of the trough or cutoff low remains somewhat low confidence. Many ensemble members are continuing to favor another cutoff upper low developing near Cape Mendocino while the mean flow to the north returns to a more zonal pattern. In this scenario, heights rising aloft and moderating mid-level temperatures would favor a warming trend at the surface, while southerly to southeasterly flow about the eastern flank of the upper low could generate convection over the Cascades. -Picard && .AVIATION...Inland, VFR conditions are expected beneath increasing cirrus clouds at or above 25 kft through this evening. A stronger marine push may result in few-sct low stratus reaching up the Columbia River to Portland-area terminals (KPDX, KHIO, KVUO, KTTD), but sufficient coverage to yield MVFR cigs is unlikely, only a 10-20% chance after 12-15z Sat. At the coast, expect low marine stratus with high-end IFR to low-end MVFR cigs to persist at KAST through 00z Sunday. Forecast cigs are a bit more uncertain at KONP. Although KONP was mostly clear as of 2130z Friday, low marine stratus will eventually move back in this evening, however the exact onset timing is uncertain and could occur anywhere between 00-05z Saturday. Given the stronger marine push this evening, suspect timing will be closer to 00z rather than to 05z. Diurnal west to northwest winds build to 5-10 kt with occasional gusts of 15-20 kt this afternoon, then diminish to 5 kt or less tonight. PDX AND APPROACHES...Continued VFR conditions expected through the period. High cirrus coverage increases through this afternoon, then scattered low clouds develop overnight as a stronger marine push takes place. There is a 10-20% chance for sufficient stratus coverage to yield MVFR cigs after 12-15z Sat before stratus mixes out by 18z Sat. Northwest winds remain around 10 kt this afternoon with gusts up to 15-20 kt, before easing to 5 kt or less after 06z Sat. -TK/Picard && .MARINE...While winds remain weak across the waters, high pressure will maintain northerly to northwesterly winds through next week, however winds will remain relatively weak and should stay under 10-15 kt. Seas should subside to 5 to 6 ft Friday evening and then stay at or below 5 ft through the upcoming week. There are no signs conditions will meet Small Craft Advisory criteria over the coastal waters at this time. -TK && .PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...None. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland