textproduct: Portland

SYNOPSIS

A prolonged atmospheric river continues to influence the Pacific Northwest, sustaining periods of heavy rainfall, breezy winds, and widespread hydrologic concerns through late Wednesday, possibly as late as early Thursday. Widespread river flooding remains likely, along with urban and small stream flooding due to persistent heavy rain. Wind may lead to downed trees and power outages due to saturated soils.

HYDROLOGY

A strong atmospheric river remains in place across southwest Washington and northwest Oregon this morning, maintaining an elevated threat of urban, river, and small stream flooding through at least late Wednesday. Significant rainfall has already fallen across much of the region since early Monday, and river responses are now well underway. Additional rainfall today through Wednesday from the second moisture surge will prolong elevated flows, with many rivers already exceeding flood stage, or forecast to exceed flood stage within the next 24-36 hours.

Rainfall over the past 24 to 36 hours has already pushed several rivers into flood stage, including record flooding on the Grays River (the old record height was 33.15 ft, which was broken around 10 PM Monday when river levels peaked around 33.4 ft), major flooding on the Naselle River, moderate flooding on the Willapa River, and minor flooding for Nehalem River, Wilson River, Trask River, Beaver Creek, East Fork Lewis River, Miami River, and Washougal River. Elsewhere, many basins continue rising and are expected to respond sharply again as periods of heavy rain continue. While the Siletz River, Cowlitz River (Kelso and Castle Rock), and Johnson Creek are currently not in flood stage or action stage, these rivers are expected to reach minor flood stage late this morning. Expect the Pudding River to reach minor flood stage by late Wednesday.

The threat for flooding along small creeks and streams as well as urban flooding, including roadway flooding, will continue through Wednesday. Latest high-resolution guidance favors a band of heavier precipitation lingering over southwestern Washington and far northwestern Oregon this morning, with rates around 0.25 inch per hour or higher. These heavy rainfall rates could make for a hazardous morning commute along the I-5 corridor from Salem north through Portland/Vancouver to Kelso/Longview with abundant water atop area roadways. Ponding of water on roads will increase risk of hydroplaning and car accidents.

Periods of heavy rain will also increase the risk for landslides in areas of steep terrain and debris flows over recently burned areas. People, structures, and roads located below steep slopes, in canyons, and near the mouths of canyons may be at serious risk from rapidly moving landslides. A Flood Watch remains in effect across all of southwest Washington and northwest Oregon from now until 4 PM Thursday, except for most of Lane County which has been removed from the Flood Watch.

AVIATION

A mixed bag of LIFR/IFR/MVFR cigs and IFR/MVFR/VFR visibilities continues across northwest Oregon and southwest Washington, with cigs and visibilities being lowest from KONP to KSLE and points north where a large band of steady stratiform rain continues. Rain will be heavy at times through Tuesday afternoon, especially during the morning and early afternoon hours north of KEUG. Rain should finally begin to taper off from south to north between 06-12z Wednesday as the aforementioned band of stratiform rain lifts northward over western Washington.

Although winds have become less gusty, occasional wind gusts up to 20-25 kt are still being observed inland and up to 30 kt at KONP. Winds will increase along the coast through the day, especially at KONP where wind gusts will likely approach 35-40 kt. The remaining TAF sites will see wind gusts increasing late this afternoon into tonight.

KPDX AND APPROACHES...Expect steady stratiform rain to persist through at least 00z Wednesday, heavy at times this morning before rain attempts becoming relatively light this evening. This will result in development of MVFR cigs between 18-21Z, then persisting throughout the TAF period, with occasional dips to IFR possible (20-35% chance) through 00z Wednesday, and then to 60-70% by 01z. Although winds have weakened this morning, expect winds to increase again towards 02-06z Wednesday when southerly to southwesterly wind gusts up to 25-30 kt are likely.

MARINE

Buoy observations from early Tuesday morning showed seas hovering around 13 to 14 ft with weakening winds. Seas should fall to 12-13 ft by Tuesday afternoon and then remain steady through Wednesday night. Seas likely fall to 10 ft or lower by Thursday afternoon. Gale force wind gusts up to 35-40 kt are expected across the inner waters with the passage of a frontal system late Tuesday into Wednesday, with gusts up to 30 kt over the outer waters. That said, gale force wind gusts are likely already occurring across PZZ253. Gusts will likely peak near 35 kt over the Columbia River Bar beginning around sunset Tuesday.

Seas and winds will likely fall below small craft advisory criteria on Friday, with relatively quiet conditions expected over the coastal waters over the weekend. -23

BEACH HAZARDS

Buoy observations from early Tuesday morning showed seas hovering around 13 to 14 ft with weakening winds. Seas should fall to 12-13 ft by Tuesday afternoon and then remain steady through Wednesday night. Seas likely fall to 10 ft or lower by Thursday afternoon. Gale force wind gusts up to 35-40 kt are expected across the inner waters with the passage of a frontal system late Tuesday into Wednesday, with gusts up to 30 kt over the outer waters. That said, gale force wind gusts are likely already occurring across PZZ253. Gusts will likely peak near 35 kt over the Columbia River Bar beginning around sunset Tuesday.

Seas and winds will likely fall below small craft advisory criteria on Friday, with relatively quiet conditions expected over the coastal waters over the weekend. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...Coastal Flood Advisory until 5 PM PST this afternoon for ORZ101-102.

WA...Coastal Flood Advisory until 5 PM PST this afternoon for WAZ201.

PZ...Small Craft Advisory until 4 PM PST this afternoon for PZZ210- 251-252.

Gale Warning from 4 PM this afternoon to 10 PM PST Wednesday for PZZ210-251-252.

Gale Warning until 4 AM PST Wednesday for PZZ253.

Small Craft Advisory from 4 AM to 10 PM PST Wednesday for PZZ253.

Small Craft Advisory until 10 PM PST Wednesday for PZZ271>273.