textproduct: Portland

SYNOPSIS

High pressure will maintain dry weather through Friday. Offshore flow will bring unseasonably warm temperatures Thursday and Friday along with gusty east winds in the western slopes of the Cascades and Columbia River Gorge. A weak cold front will bring chances for light rain late Friday night into Saturday, before high pressure brings a quick return to dry weather Saturday night into Sunday. Chances for widespread rain return Monday into early Tuesday with an approaching low pressure system, although model guidance has been trending drier.

SHORT TERM...Tonight through Friday night

Water vapor satellite imagery this afternoon shows drier air aloft moving overhead as a weak upper level trough moves out of the region, while upper level ridging amplifies over the northeast Pacific. This ridge of high pressure will continue to build over the region and into western Canada on Thursday. Surface high pressure builds into western Montana while a surface thermal trough develops along the Oregon coast Thursday morning. This will lead to a period of offshore flow with east winds through the Columbia River Gorge and western slopes of the Cascades. Warming aloft coupled with dry, downsloping winds will bring unseasonably warm temperatures across the area Thursday and Friday.

Model guidance remains in good agreement for widespread high temperatures warming into the mid to upper 70s both days, including at the coast on Thursday. A few locations may see temperatures reach 80 degrees, with around a 10-60% chance along the I-5 corridor, highest chances south and east. 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). Could be our last "hot" day of the year, as we typically see temperatures drop off during the second half of October.

East winds will also become gusty by Thursday morning, especially through the Columbia River Gorge into the eastern Portland Metro area. Model guidance suggests surface pressure gradients increase to around -5 to -6 mb which could produce wind gusts up to 25-35 mph, except up to 45-50 mph on wind-prone exposed ridgetops. Pressure gradients likely begin to slacken later Friday morning with winds easing by the afternoon. Onshore flow returns by late Friday night ahead of an incoming cold front. /DH

LONG TERM...Saturday through Tuesday Night

There is high confidence among ensemble guidance for cooler temperatures this weekend as a weak cold front swings through the region and brings chances for light rain. Light rain begins at the coast Friday night, mainly from Lincoln City northward. Rain chances spread inland Saturday morning, peaking around 40-60% across the south Washington and north Oregon Cascades, 25-50% along the I-5 corridor from Salem northward, and 10-20% south of Salem. Rain amounts, if any, will be light. Conditions quickly dry out Saturday night to Sunday as transient shortwave ridge passes through. Expect seasonable temperatures in the 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, bringing increased chances for widespread rain between early Monday morning and Tuesday morning. This system has the potential, albeit low, to bring a more meaningful amount of rain considering how dry conditions have been thus far this October. The NBM currently shows a 20-35% chance for at least 0.25 inches of rain between 5 AM PDT Monday and 5 AM PDT Wednesday. Probs continue to come down as there are an increasing number of ensemble members showing a solution where the upper-level trough remains farther offshore or progresses farther south into California, limiting the amount of rain in our area. Chances for impactful wind gusts over 40 mph are currently less than 10% with this system. DH/10/23

AVIATION...Through 00Z Friday

Along the north OR and south WA coast, including KAST, CIGs will fluctuate between high-end MVFR (2-3 kft) and VFR through around 22-23z Wed as a weak front brushes SW WA. Otherwise, VFR conditions across the airspace with mostly clear skies. Northerly to northwesterly winds around 5-10 kt for most terminals. Strengthening offshore pressure gradients between KTTD and KDLS will result in increasing easterly winds after 06z Thu along the west slopes of the Cascades and Coast Range into the coast. East winds will be strongest through the Columbia River Gorge with gusts up to 25-35 kts. These stronger east winds reach KTTD after 12-15z Thu where winds could gust up to 25-30 kts. Winds remain north 5-10 kts in the Willamette Valley.

KPDX AND APPROACHES...VFR conditions with mostly clear skies through the TAF period. Northwesterly winds 4-6 kt. -03

MARINE

Benign marine conditions continue. Southerly winds are turning northerly to northeasterly this afternoon, continuing through the end of the week. Winds turn southerly again over the weekend and into early next week as a series of fronts pass through the waters. Seas remain around 4-7 ft this week with periods of 12-14 seconds.

A steeper northwesterly swell arrives this weekend, building seas to 7-9 ft by Sunday and 10-12 ft early next week. There is a 10-20% chance for seas exceeding 15 ft on Monday, with the highest chances north of Cape Falcon 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.