textproduct: Portland

SYNOPSIS

High pressure will maintain dry weather through Friday. Offshore flow will bring unusually warm temperatures Thursday and Friday along with gusty easterly winds in the Cascades, Cascade foothills, and Columbia River Gorge. A weak cold front will bring chances for light rain Friday night into Saturday, before high pressure brings a quick return to dry weather Saturday night into Sunday. Increasing chances for widespread rain Monday into early Tuesday morning with an approaching low pressure system.

SHORT TERM...Today through Friday night

Radar imagery as of early Wednesday morning depicts light right moving into the Olympic Peninsula as a weak cold front swings through British Columbia and far northwest Washington. Through the rest of the morning, there is a 15-30% chance at any given hour for light showers clipping part of the south Washington coast including the Long Beach Peninsula and Willapa Hills. Otherwise, expect dry and warm conditions for the rest of southwest Washington and northwest Oregon today as the region remains under an upper- level ridge.

Temperatures will peak Thursday and Friday as upper-level ridging amplifies over the Pacific Northwest and low-level offshore flow develops. Model guidance remains in good agreement for widespread high temperatures between 75-80 degrees on both days for interior valleys, and around 65-70 degrees along the coast. Although this forecast for interior valleys is around 10-15 degrees above normal for mid-October, record high temperatures should be out of reach for most locations. Eugene is the only location that has a small chance to tie or break their current record of 81 degrees back in 2002, as this site has a 10-20% chance of reaching 81 degrees or warmer this Friday.

In addition to warmer temperatures, winds will become gusty out of the east across the Cascades, Cascade foothills, Columbia River Gorge, and far eastern Portland/Vancouver Metro beginning tonight. This is in response to a tightening surface pressure gradient as ensemble guidance is showing pressure gradients between Troutdale and The Dalles peaking around -5 to -6 mb on Thursday. As such, the aforementioned areas should expect max wind gusts as high as 25-35 mph, except up to approximately 45 mph on wind-prone exposed ridgetops and in the western Gorge. By Friday, pressure gradients slacken and winds will gradually weaken throughout the day. Beyond a few small downed tree branches where wind gusts are strongest, impacts are not expected. For the rest of northwest Oregon and southwest Washington, winds out of the north/northeast should remain under 10-15 mph. Onshore flow returns by late Friday night ahead of an incoming Pacific cold front. This front will bring chances for light rain to the area Friday night into Saturday, which is discussed below in the long term discussion. -10/23

LONG TERM...Saturday to Tuesday

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. Rain chances (30-50%) begin 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, 25-45% along the I-5 corridor from Salem northward, and 15-20% south of Salem. Rain amounts will be light and non-impactful. 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 early Tuesday morning. Rain could begin as early as Sunday evening along the north Oregon coast (10-20% chance), however the vast majority of ensemble guidance holds rain off until late Sunday night or Monday morning. This system has the potential to bring a more meaningful amount of rain considering how dry conditions have been thus far this October, and the NBM currently shows a 30-50% chance for at least 0.25 inches of rain between 5 AM PDT Monday and 5 AM PDT Wednesday. Chances have come down since yesterday as there are some ensemble members now showing a solution where the upper-level trough remains further offshore or progresses further south into California, limiting the amount of rain in our area. Fortunately, rain from this system won't be heavy or persistent enough cause flooding. Chances for impactful wind gusts over 40 mph are currently less than 10% with this system. -10/23

AVIATION...Through 12Z Thursday

Radar and satellite imagery as of early Wednesday morning depicts mid to high level clouds across the region along with light showers along the south Washington coast as a weak front moves through the Olympic Peninsula. Given that this system is tracking further north, conditions remain predominately dry and VFR for most terminals throughout the TAF period. An exception is KAST, where CIGs are jumping between low- end MVFR (1-2 kft) and VFR this morning with showers in the vicinity. After 17-19z Wed, conditions quickly dry out as high pressure builds. Clouds will gradually clear out this afternoon. Northerly to northwesterly winds around 5-10 kt today for most terminals. Strengthening offshore pressure gradients between KTTD and KDLS will result in increasing easterly winds tonight.

KPDX AND APPROACHES...VFR with mid to high level clouds through this morning. After 18-19z Wed, high clouds gradually clear out into mostly sunny skies. Northwesterly winds 4-6 kt. -10

MARINE

Benign marine conditions expected this week. Southerly winds continue today due to a weak front, then return northerly to northeasterly by 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 10-25% 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.