textproduct: Portland

SYNOPSIS

High pressure will remain in place across the region through Friday, maintaining dry weather with mild temperatures, warmest in the Oregon Cascade foothills and along the central Oregon coast. Skies will remain mostly clear, aside from low stratus and areas of dense fog during the overnight/morning hours in the central and southern Willamette Valley. Meanwhile, strengthening easterly flow through the Columbia River Gorge will lead to windy conditions in the eastern Portland/Vancouver metro and adjacent higher terrain through Thursday. Widespread rain returns Saturday into Saturday night.

DISCUSSION...Now through Tuesday night

Expect the ongoing weather pattern to persist through Friday as high pressure remains in place over the region, maintaining dry conditions with warmer than normal temperatures. In fact, record high temperatures will be possible in some areas, especially in the Portland metro, northern Willamette Valley, central Oregon coast and Oregon Cascade foothills. Forecast highs in these areas are generally in the 60s today and tomorrow, except approaching 70 degrees from Tillamook to Florence and in the Oregon Cascade foothills from Lyons southward to Oakridge. The reason these locations will be so warm is due to a combination of abundant sunshine and downsloping easterly winds, resulting in both compressional heating and diurnal heating. The coolest locations will be south of Salem in the Willamette Valley where stubborn low stratus and areas of dense fog during the overnight/morning hours will limit daytime heating. Note air stagnation concerns will persist in these areas through Thursday evening/night, including the Cowlitz Valley. This means air quality may become degraded over time. Note the central Columbia River Gorge and Upper Hood River Valley will also be relatively cooler with highs in the 40s and lower 50s along with some low clouds, however these areas have relatively stronger transport winds and less air stagnation concerns.

Meanwhile, windy conditions will persist in the western Columbia River Gorge, Troutdale, and Washougal area. These locations should expect easterly winds sustained around 25 to 35 mph with gusts up to 40 to 45 mph through 1 PM PST Thursday, and even stronger than that in typical windy spots in the western Gorge such as Crown Point. It appears wind speeds will peak in strength after 3 AM PST Thursday when the surface pressure gradient from Troutdale to the Dalles reaches -6 to -8 mb. Wind Advisories remain in effect for the Troutdale and Washougal area to cover this threat, as some tree damage and power outages will be possible, albeit nothing overly significant for this time of year.

The weather pattern will begin to change on Saturday in response to an incoming Pacific frontal system. As this system approaches, cloud cover will increase from west to east across western WA/OR early Saturday morning. By late Saturday morning/early afternoon, rain is expected to begin at the coast (90% chance). Rain will then spread inland from west to east all the way to the Cascades during the afternoon and evening hours. Note snow levels will be high (likely above 6000-7000 feet) when precipitation begins due to a warm front lifting northward over the area, meaning rain will fall at pass level. Widespread rain then remains in the forecast through the weekend as a trailing cold front pushes through on Sunday. Post-frontal showers should persist Sunday night through Monday while snow levels fall rapidly fall to around 3000-3500 feet, bringing some snow to the Cascade passes. That being said, QPF lowers substantially at that point as precipitation will be light and showery. This will limit snow totals in the Cascades, most likely only amounting to 1 to 4 inches. Snow amounts of 6 inches or more cannot be completely ruled out, however probabilities for this to occur are low at 10-15%. It appears conditions will trend drier and colder Monday night through Tuesday night, however some light and non-impactful showers may linger (20-50% chance, highest at the coast). -23

AVIATION

Dry south to southwesterly flow aloft as an upper level ridge of high pressure persists over the region. This will maintain primarily VFR conditions except for areas of fog or low stratus that develops, mainly within parts of the southern and central Willamette Valley. With a strong surface inversion in place, expect a return of LIFR fog to parts of the southern and central Willamette Valley, with highest chances again near KEUG, increasing to around 50-60% by 08-10z Thursday. A strong offshore pressure gradient through the Columbia River Gorge will maintain breezy east winds into the east Portland metro. Expect gusts up to 35 kt at KTTD through Thursday.

KPDX AND APPROACHES...VFR conditions expected with scattered high clouds. Diurnally driven southeast winds around 5-10 kt expected at the terminal, while east approaches will see stronger east winds with gusts up to 35 kt near KTTD. /DH/03

MARINE

High pressure inland will maintain light offshore winds across the waters through Thursday. East winds with gusts up to 15-20 kt will be possible near gaps in the coastal terrain. Winds turn southerly by late Thursday and gradually increase Friday into the weekend as a front approaches the waters by Saturday. There is around a 40-60% chance for maximum wind gusts to exceed 34 kt on Saturday, but the chance for widespread gales remains low.

A persistent southwest to westerly swell at around 13-15 seconds will maintain seas around 9 to 12 ft through the end of the week. Will maintain the Small Craft Advisory across all coastal waters including the Columbia River Bar through Friday. Southerly winds waves are expected to build on Saturday maintaining elevated seas of around 10 to 12 ft. Relatively active weather continues into early next week. /DH

BEACH HAZARDS

A mid-period westerly swell brings an enhanced threat for sneaker waves through tonight. A Beach Hazards Statement is in effect until 1 AM PST Thursday for the coasts of northern/central Oregon and southern Washington. Waves will be able to run significantly farther up on a beach than normal, including over rocks and jetties. Sneaker waves can suddenly knock people off of their feet and quickly pull them into the frigid ocean which may lead to serious injury or drowning. Caution should be used when in or near the water, especially those who will be razor clamming this week.

PQR WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory until 10 PM PST Friday for ORZ108- 115>118-123>125.

Wind Advisory from 10 PM this evening to 1 PM PST Thursday for ORZ112.

WA...Air Stagnation Advisory until 10 PM PST Friday for WAZ204-205.

Wind Advisory from 10 PM this evening to 1 PM PST Thursday for WAZ207.

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