


Area Forecast Discussion
Issued by NWS Portland, OR
Issued by NWS Portland, OR
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879 FXUS66 KPQR 170958 AFDPQR Area Forecast Discussion National Weather Service Portland OR 258 AM PDT Fri Oct 17 2025 .SYNOPSIS...Transient shortwave ridging Friday night will bring chilly overnight temperatures and areas of frost for some inland valleys. A robust frontal system arrives late Saturday into Sunday, bringing widespread soaking rain to the area with gusty southerly winds. Trending drier Sunday night into early next week, however some uncertainty remains with a 20-45% chance of rain returning by Wednesday. && .SHORT TERM...Now through Sunday Night...Satellite, radar and surface weather observations from early Friday morning depicted a decaying cool front draped over far northwest Washington, extending southwestward into the coastal waters. This front should continue weakening as it slowly sags southward into southwest Washington and northwest Oregon, resulting in very little to no measurable rainfall for most locations. The main exception will be in the south Washington Cascades/foothills and along the south Washington/north Oregon coast. These areas have an 80-90% chance for at least 0.05" of rain. Transient ridging builds into the area this afternoon into early Saturday, setting the stage for clear skies and calm winds. This will lead to chilly temperatures once again for inland valleys Friday night into Saturday morning. The coldest areas will likely be the Upper Hood River Valley, south WA Cascade foothills, Battle Ground and Ridgefield areas. Confidence is generally over 70-80% these zones will see low temperatures dip to 33-36 degrees, which has prompted the issuance of Frost Advisories Friday night into Saturday morning. Meanwhile, a Freeze Warning is in effect for the Upper Hood River Valley for low temperatures as cold as 29-30 degrees. While frost is also possible in portions of the southern Willamette Valley, especially east of I-5, confidence is currently not high enough to include these zones in the Frost Advisory. This is due to potential low clouds or fog that may develop instead of frost; the HREF currently shows a 50-75% chance for low cloud development mid to late Friday night, which would favor temps bottoming out in the upper 30s with minimal frost concerns. The overall weather pattern beyond Friday morning does not favor widespread frost or freeze concerns, so this round of frost/freeze headlines may wind up being the last of this growing season. Despite the chilly temperatures in place Saturday morning, temperatures will rebound nicely in the afternoon with highs in the 60s, except near 70 degrees in Eugene-Springfield, Creswell, Blue River, Lowell and Oakridge. These areas will see sunny skies throughout the day, however northern areas will see clouds begin to increase ahead of the next frontal system. Models are in good agreement on the timing of this front, bringing stratiform rain to southwest Washington and the north Oregon coast Saturday evening and then the rest of northwest Oregon from Lane County northward Saturday night into Sunday morning. Persistent stratiform rain will transition to post-frontal showers by late Sunday morning or early Sunday afternoon. This is when forecast soundings show 850 mb temperatures cooling to +1 to +2 degrees Celsius, with SBCAPE values increasing to 100-200 J/kg and equilibrium levels generally below -10 degrees Celsius. However, 0-3 km AGL bulk shear values are fairly high at 30-35 kt (have opted to use 0-3 km AGL bulk shear values instead of 0-6 km as cloud tops generally look to stay near or below 3 km). Both speed shear and directional shear are in place, as the wind direction will veer with height for a few hours or so as the upper level trough axis moves overhead. The limited instability and shallow nature of Sunday`s convection suggests overall lightning activity will most likely be limited (which helps explain why NBM thunder probabilities only peak around 10-15%). However, whether lightning occurs or not, stronger showers will have the potential to produce a funnel cloud, landspout, or gusty outflow winds up to 45 mph given the environmental wind profile in place, meaning highly localized wind damage is possible. Note southerly winds will be breezy in general Saturday night and Sunday, even away from showers and thunderstorms. Currently expecting southerly wind gusts up to 20-30 mph for inland areas and up to 30-40 mph for the south WA/north OR coast. Gusts up to 40-50 mph appear likely in the high Cascades. Winds will weaken Sunday night while any lingering showers begin to dissipate. -23 .LONG TERM...Monday through next Friday...Most model guidance suggests dry weather with seasonable temperatures, relatively light winds and a mix of clouds and sun Monday and Tuesday. That said, there remains a handful of GEFS/ENS ensemble members with light QPF amounts Monday morning/afternoon and Tuesday morning/afternoon as a pair of weak upper level impulses move overhead. As such, there is a 10-30% chance of light rain showers on Monday and 15-35% chance on Tuesday. Probabilities are highest along the south WA/north OR coast. Chances for rain gradually increase late Wednesday through Thursday night, peaking near 75-85% by early Friday morning. This system has the potential to bring more impactful rain amounts and gusty south winds, however uncertainty is high in regards to exact rain amounts and exact wind speeds, as the outcome will be highly dependent on the exact track and strength of a negatively tilted trough and associated deepening surface low that will be moving somewhere over the coastal waters during that time. Ensemble low locations vary significantly both spatially and temporally, with some ensemble guidance suggesting a fairly weak low with minimal impacts, while other members suggest a very strong low capable of wind damage somewhere along the Washington, Oregon, or northern California coast. There is currently a 15-25% chance for max wind gusts of 45 mph or stronger across all of northwest Oregon and southwest Washington, except for a 35-50% chance at the coast and on exposed ridges in the Coast Range and Cascades. This system will also bring a 40-80% chance of 1" of rain or more, with the lowest probabilities in the Portland metro and Willamette Valley west of the I-5 corridor and the highest probabilities in the mountains and at the coast. -23 && .AVIATION...A weak cool front will continue sagging southward over southwest WA and far northwest OR this morning, bringing MVFR cigs to the coast. MVFR cigs have already developed at KAST, and should spread southward down to KONP around 12-14Z Friday as the front progresses. It appears inland areas will remain VFR through 12-15z Friday before a brief period of MVFR cigs between 15-18z Friday as the front decays overhead. There is a 60-80% chance for cigs below 3000 ft at all inland terminals, except 30-40% at KEUG). Winds will remain light and variable around 5 kt or less at all TAF sites through 12z Saturday. KPDX AND APPROACHES...VFR CIGs through the TAF period, with cigs likely lowering to around 2800-3000 ft after 12-15z Fri with a weak frontal passage (75% chance for cigs at or below 3000 ft). Light and variable winds under 5 kt continue. -23 && .MARINE...Winds return to a northerly direction behind a weak frontal passage Friday morning around 10-15 kt as high pressure rebuilds. Seas hold around 4-6 ft at 14-15 seconds. Conditions become more active on Friday evening as a northwesterly swell enters the waters due to a low pressure system over the Gulf of Alaska. This swell will build seas to 11-13 ft at 14-16 seconds, resulting in hazardous conditions for small craft. Small Craft Advisories go into effect across all waters including the Columbia River Bar 5 PM Friday and last through at least Saturday evening. Winds will stay rather tame out of the north with gusts up to 10-15 kt into Saturday morning. The weather pattern remains active Saturday night into early next week as a stronger frontal system progresses through the waters and brings breezy southerly to westerly winds. Marine conditions quickly amplify as a higher northwesterly swell enters the waters, building seas above 15 ft at 15 seconds (>90% chance) on Sunday. Chances for seas above 20 ft have decreased and are now near 0%, indicating increasing confidence is the wave height forecast. In addition to increasing seas, winds will likely gust up to 25-30 kt. Brief and isolated gale forced wind gusts up to 35 kt are possible over the northern inner waters with the frontal passage Saturday night into early Sunday morning, including the main channel of the Columbia River Bar. Seas will decrease later Monday into Tuesday morning, bottoming out around 8-10 ft at 13 seconds before another potent northwesterly swell arrives Tuesday afternoon and evening pushing seas into the 10-15 ft range again. -23/10/99 && .BEACH HAZARDS...A northwest swell of 10-12 ft at 15 to 18 seconds seconds is expected to enter the waters Friday evening. This increase in wave energy will support a high threat for sneaker waves through this weekend. A Beach Hazards Statement remains in effect across the Central and Northern Coast of Oregon and the South Washington Coast, which is now in effect through Sunday evening. Sneaker waves can run up significantly farther on a beach than normal, including over rocks, logs, and jetties. Sneaker waves can suddenly knock people off of their feet and quickly pull them into the ocean which may lead to serious injury or drowning. Caution should be used when in or near the water. Always keep an eye on the waves, and be especially watchful of children and pets. Remember, never turn your back on the ocean! -23/10/99 && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Frost Advisory from midnight tonight to 9 AM PDT Saturday for ORZ104. Freeze Warning from midnight tonight to 9 AM PDT Saturday for ORZ121. WA...Frost Advisory from midnight tonight to 9 AM PDT Saturday for WAZ205-208. PZ...Small Craft Advisory from 5 PM this afternoon to 2 PM PDT Saturday for PZZ210. Small Craft Advisory from 5 PM this afternoon to 8 PM PDT Saturday for PZZ251>253-271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland