textproduct: Portland

SYNOPSIS

High pressure will result in dry and warm conditions across the area today and Monday. A significant pattern change begins on Tuesday with a return of cooler temperatures, rain, and breezy southerly winds through the end of the week. Wednesday and Thursday are expected to be the wettest days with also a 10-20% chance for thunderstorms. Conditions trend slightly drier over the weekend, but there remains chances for lingering showers.

LONG TERM...Wednesday through Saturday

Wednesday into Thursday will be the more significant soaker days as the majority of ensemble members are showing a second, much deeper upper-level trough dropping down into the Pacific Northwest. The associated surface front swings through on Wednesday, bringing widespread rain, cooler temperatures, and breezy winds from the south. In addition, there will be a 10-20% chance for thunderstorms. Chances for exceeding 1 inch of rain in 48 hours between 5 AM Wednesday to 5 AM Friday are high (70-90%) across northwest Oregon and southwest Washington, with the highest chances along the coast, Coast Range, and Cascades. Chances for exceeding 2 inches during this same timeframe are around 30-50% for these higher terrain features, and 5-15% along the I-5 corridor. Orographic enhancement will play a big role with providing higher rainfall amounts to the mountains.

Thursday afternoon to Saturday, the upper-level trough remains over the Pacific Northwest and we transition into a post-frontal environment with lingering showers. Given that there will be cooler air aloft, this will favor increasing atmospheric instability and thus chances for thunderstorms. There will be another 10-20% chance for thunderstorms on Thursday following the initial frontal passage. Any passing thunderstorms may produce lightning, heavy rain, erratic winds, and small hail. Overall, while the upcoming rain will not quite yet be a "fire season ender," it will definitely slow down fire season and help put a damper on ongoing wildfires. -10

AVIATION...Through 00z Tuesday

VFR conditions favored across the airspace throughout the period. Sct-bkn low clouds linger across far northwestern OR and southwestern WA per satellite imagery as of 21z Sun, with largely clear skies elsewhere. North to northwest winds of 5-10 kt inland and 10-15 kt with gusts as high as 20-25 kt along the coast and in the southern Willamette Valley this afternoon will ease to 5 kt or less after 03-06z Mon. Light offshore (north to northeast) flow overnight will limit chances for MVFR cigs beneath low clouds to 20-30% along the coast and in the Willamette Valley.

KPDX AND APPROACHES...VFR conditions expected throughout the period. Coverage of lingering low clouds will not restrict cigs this afternoon. Northwest winds of 5-10 kt will ease below 5 kt tonight, with low chances, only 10% after 09z Mon, for MVFR cigs if low cloud coverage is higher than expected overnight. -36

MARINE

Transient ridging over the Northeast Pacific will see northerly to northwesterly winds continue into Tuesday morning. Thermal troughing along the coast will yield strengthening near- shore winds Monday afternoon, reaching 15-20 kt with gusts to 25 kt within 10-20 NM north of Cape Falcon and including the Columbia River Bar, where a Small Craft Advisory has been hoisted from 2 PM to 8 PM PDT Monday afternoon and evening. Largely wind-driven seas will persist at 4-6 ft during this period.

On Tuesday, winds back out of the south-southwest as a broad pattern shift sees troughing develop over the Northeast Pacific while ridging moves inland. By Wednesday, a robust frontal system will traverse the coastal waters of OR/WA. Southerly winds ahead of the frontal passage are likely (50-75% chance) to yield at least intermittent gale-force gusts. Sustained winds are less likely (30-60% chance) to reach gale- force, with higher chances generally to the north and closer to shore. Gale Watches may be needed if confidence persists in the duration of potential gusty winds across enough of the coastal waters. These strong winds will also see seas build to 8-12 ft, with chances for significant wave heights to reach 15 ft remaining less than 10%. Behind this system, winds and seas should ease from late in the week into next weekend. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 2 PM to 8 PM PDT Monday for PZZ210- 251.