textproduct: Portland

SYNOPSIS

An active and unsettled pattern remains across northwest Oregon and southwest Washington as multiple Pacific disturbances continue to rotate inland through midweek. Periods of rain at lower elevations and snow in the Cascades persist. Attention remains focused on Wednesday, when a developing low pressure system may bring impactful winds depending on its eventual track. While uncertainty remains, ensemble guidance now suggests a modest tilt toward a coastal solution. Conditions trend quieter later in the week as upper-level ridging attempts to build over the region.

DISCUSSION...Now through Monday

This afternoon, the region sits beneath a brief window of weak mid-level ridging embedded within a much larger-scale trough over the eastern Pacific. This has allowed precipitation to become more light and scattered in elevated terrain, and generally a lull or lack of precipitation in the lowlands. This pause in precipitation will be brief. Snow levels begin to rise into tonight, bringing a halt to winter travel conditions in the Cascades.

Conditions begin to change later tonight into early Wednesday as the broader synoptic pattern becomes increasingly amplified. Rain will return to the area. The parent upper-level trough offshore continues to evolve toward a closed low configuration while dropping southward, allowing additional shortwave energy to rotate northward toward the Pacific Northwest. This evolution introduces substantial forecast sensitivity, particularly with respect to the development and track of a meso-low.

Ensemble guidance remains divided, though some clarification has emerged since earlier cycles. The European ensemble is now evenly split, with roughly half of its members tracking the surface low inland and half favoring a coastal path. In contrast, the GFS ensemble strongly favors a coastal track, with approximately 95% of members keeping the low near the coastline and only minimal support for an inland solution. The Canadian ensemble leans the opposite direction, with about 60% of members favoring an inland track and 40% along the coast. When considering all guidance collectively, the overall signal suggests roughly a 60% probability of a coastal track versus a 40% chance of the system moving inland.

This distinction remains critical, as a coastal track would support stronger pressure gradients across western Oregon and southwest Washington, increasing the potential for impactful winds. Under this scenario, a period of strong winds would be possible Wednesday morning into early afternoon, potentially affecting not only coastal areas but also inland valleys, including portions of the I-5 corridor. Gusts could exceed advisory criteria (of 45+ mph gusts), and in the higher-end outcomes (10-20% chance), reach levels capable of producing scattered to widespread tree damage and power outages. Note that while the storm system will only take about 6-12 hours to move through the area, any given location will likely only see peak wind gusts for 1 to 2 hours. As for an inland track, this would substantially limit wind impacts, confining stronger gusts to higher terrain and the immediate coast.

Given the remaining uncertainty, the forecast continues to favor a middle-ground solution where winds remain within Wind Advisory criteria, while advertising the low potential for a more significant wind event (High Wind criteria of 58+ mph). Confidence in exact timing and magnitude remains moderate at best, and trends in upcoming model cycles will be critical in determining whether higher-end wind headlines become necessary.

Beyond Wednesday, ensemble guidance generally supports a gradual eastward progression of the amplified trough. This would keep periodic chances for rain and mountain snow in the forecast, especially along the coast and higher terrain. A weaker frontal feature is likely to move through later Thursday, followed by increasing support for temporary ridging aloft toward the end of the week. Should this ridging materialize, it would provide a brief window of drier and calmer weather heading into the weekend, though confidence in its duration and strength remains moderate. ~12

AVIATION

MVFR/VFR conditions will continue across the region with areas of rain moving in from SE to NW through the TAF period. Precipitation will continue to stream in across the airspace and will bring rain to the majority of TAF sites by 08Z-10Z Wednesday. A rapid pattern change in the forecast through 12Z Wednesday. The biggest issue will be wind. For sites impacted by the Columbia River Gorge (KTTD, KPDX and KHIO especially), the east winds will increase into the 15 to 25 kt range between 09Z and 11Z Wednesday. For ALL the TAF sites, look for a sudden shift in winds coming from the south and increasing into the 25 kt to 45 kt range with a brief period of time where gusts to 50 kts could be possible. Expect the potential for the 50 kt gusts for about 1 to 3 hours, which will start in the south at KEUG around 15Z Wednesday, reaching KSLE around 18Z Wednesday and towards KPDX/KHIO/KTTD around 22Z Wednesday-00Z Thursday. South/southwest gusts of 30 kt or higher, for coastal locations look to start around 15Z-17Z Wednesday with peak winds expected around 18Z-21Z Wednesday with southern locations seeing the elevated winds first. Overall, winds are expected to decrease rapidly after 00Z-03Z Thursday across the airspace.

Note: Have done my best to highlight LLWS potential for TAF locations. However, there is a general increase in both speed and direction LLWS from around 12Z Wednesday though around 06Z Thursday for the entire airspace as a result of the incoming system.

KPDX AND APPROACHES...MVFR/VFR conditions will continue with rain moving in from SE to NW through the TAF period. A rapid pattern change in the forecast through 12Z Wednesday. East winds will increase into the 15 to 25 kt range between 09Z and 11Z Wednesday. Then winds will become southerly and increase significantly around 18Z Wednesday, with gusts up to 40 kt. Could see brief gusts up to 50 kt for a few hours around 17Z-22Z Wednesday. LLWS (both speed and direction) will be a concern after 10Z Wednesday through around 00Z Thursday. Winds drop rapidly around 00Z-03Z Thursday. /42

MARINE

Current buoy obs continue to show elevated Small Craft conditions across all waters. Seas in the 9 to 12 ft with robust easterly winds. A very active weather pattern is expected to develop across all waters through late tonight and into Wednesday. A low moving northward along the coast from California will bring elevated winds and seas across all waters. The current forecast has southerly gusts up to 50 kt across all waters and the Columbia River Bar. Isolated gusts up to 65 kt could be possible with this system, but the probability it relatively low at this time (10-15%). Seas are also expected to build towards 11-14 ft. As a result have upgraded the Gale Watch to a Gale Warning, starting late Tuesday night. A lot of uncertainty remains with the exact track and overall strength of this incoming low. So, please keep an eye on the forecast as it could easily change over the next 12-36 hours. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...Wind Advisory from 7 AM to 4 PM PST Wednesday for ORZ104>118- 123>125.

WA...Wind Advisory from 7 AM to 4 PM PST Wednesday for WAZ202>208.

PZ...Small Craft Advisory until 4 AM PST Wednesday for PZZ210-251>253- 271>273.

Gale Warning from 4 AM to 4 PM PST Wednesday for PZZ210-251>253- 271>273.