textproduct: Portland

SYNOPSIS

High pressure and offshore easterly winds will bring dry and unseasonably warm temperatures today and Friday. The strongest easterly winds are expected along the Columbia River Gorge and western slopes of the Cascades. A weak cold front will bring chances for light rain late Friday night into Saturday, before high pressure returns dry weather Saturday night into Sunday. The next chances for rain are Monday into early Tuesday with an approaching low pressure system, although guidance continues to trend drier.

SHORT TERM...Today through Friday night

Satellite imagery and surface observations as of early Thursday morning depict mostly clear skies across northwest Oregon and southwest Washington as an upper-level ridge moves overhead. Will likely remain clear through the morning, though there is a low (10-20%) chance that some stratus develops across the Willamette Valley through 8-9 AM.

Today and Friday will be the warmest days of the week, with high temperatures forecast in the upper 70s across interior valleys and 60s along the coast. Some locations may even reach 80 degrees, with a 10-30% chance along the I-5 corridor and a 50-70% chance along valleys of the Cascade foothills. Although high temperatures are expected to be around 10-15 degrees above normal for mid-October, most locations are not expected to break any records (which were mainly set back in 2022). These could be our last "hot" days of the year, as we typically see temperatures drop off during the second half of October.

In addition to warm temperatures, will also see increasing offshore easterly winds beginning this morning along the Columbia River Gorge, eastern Portland/Vancouver Metro, Cascades, and Cascade foothills. Model guidance continues to suggest surface pressure gradients tightening to -5 to -6 mb between Troutdale and The Dalles, producing wind gusts up to 25-35 mph, except up to 45-50 mph on wind-prone exposed ridgetops. Pressure gradients slacken later Friday morning with winds easing by the afternoon. Onshore flow returns by late Friday night into early Saturday morning ahead of an incoming weak cold front. -10/DH

LONG TERM...Saturday through Wednesday

The aforementioned front will quickly swings through on Saturday, returning cooler temperatures and chances for light rain. Bulk of the precipitation is aimed towards British Columbia and far northwest Washington, so the further south you go in northwest Oregon such as Lincoln County or the southern Willamette Valley, the more likely conditions remain completely dry. Chances for rain totals exceeding 0.10 inch from 5 PM Friday to 5 PM Saturday are only 5-15% from Salem to Longview, and 10-30% along the coast from Tillamook northward and the south WA/north OR Cascades. Conditions quickly dry out Saturday night to Sunday as transient shortwave ridge passes through. Expect seasonable temperatures in the mid to upper 60s across interior valleys and 50s along the coast and Cascades.

Monday to Tuesday, the majority of ensemble members are in agreement that an upper-level trough from the northeast Pacific will approach the Pacific Northwest, returning chances for rain between early Monday morning and late Monday night. Will note that these chances have gone down significantly, as of 75% of ensemble members are now showing this trough staying further offshore and progressing southward toward California rather than moving completely over the Pacific Northwest. If this scenario occurs, precipitation would be limited in our area. Chances for 24-hour rain totals exceeding 0.25 inch between 5 AM Monday to 5 AM Tuesday have fallen to 15-20% along the coast, Coast Range, and Willapa Hills, and 5-10% along the I-5 corridor.

By Wednesday, ensembles have the upper trough swinging into central California, while weak high pressure re-builds over the Pacific Northwest, favoring predominately dry conditions. At the same time, it does appear that another upper-level trough will begin to approach British Columbia and potentially make its way down into the Pacific Northwest late next week, returning chances for precipitation. -10

AVIATION...Through 12Z Friday

Satellite imagery and terminal observations as of early Thursday morning depict predominately VFR conditions with clear skies across northwest Oregon and southwest Washington as an upper-level ridge moves over the Pacific Northwest. Expect mostly clear conditions to continue through the morning, though there is a 10-20% chance for some MVFR stratus or lower across the central/southern Willamette Valley at any given hour through 15-16z Fri. There is also some shallow fog around the Portland Metro Area bringing localized VIS drops to 5SM (such as in KHIO) which may continue for the next few hours. Otherwise, sunny skies prevail today.

Offshore flow increases this morning as pressure gradients tighten. The strongest winds are expected through the Columbia River Gorge and eastern Portland/Vancouver Metro Area, bringing gusts of 24-26 kt to KTTD, and 21-23 kt to KPDX after 18-21z Fri. Will also see easterly winds along the coast as well, however, those winds generally remain under 10 kt today. For the rest of the central and southern Willamette Valley, expect light northerly to northeasterly winds.

KPDX AND APPROACHES...VFR with clear skies through the TAF period. West/northwesterly winds less than 5 kt through 13-14z Thu, then turning easterly. Easterly winds increase this afternoon with gusts up to 21-23 kt. Winds gradually weaken after 04-06z Fri. -10

MARINE

Benign marine conditions continue. A thermal trough along the coast will bring light, east/northeasterly winds through this morning. Later this afternoon, the thermal trough will break down, returning northerly to northwesterly winds over the waters. A series of fronts passing through the waters will turn winds southerly Friday night into Saturday morning, and Sunday night into Monday. Seas remain around 4-7 ft at 10-12 seconds through early Saturday morning.

A steeper northwesterly swell arrives this weekend, building seas to 7-9 ft by Saturday evening and 10-12 ft early next week. There is a 5-15% chance for seas exceeding 15 ft on Monday, with the highest chances north of Cape Foulweather and beyond 30-40 NM. Will also note that the long periods from the swells will result in a moderate sneaker wave threat this week. Caution should be used when in or near the water. -10/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.