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

Prevailing VFR conditions expected across NW OR and SW WA through the majority of the TAF period. Light offshore (north to northeast) winds overnight will limit chances for MVFR cigs to 20-30% along the coast and in the Willamette Valley. Winds will generally remain light less than 6 kts through Monday morning. East winds through the central Columbia River Gorge will locally increase to 12-15 kts with gusts up to 20-25 kts through the day Monday. An approaching weather system will slow shift winds back offshore (west to northwest), first along the coast around 18z Mon with northwest winds increasing to 10-14 kts through 03z Tue around and north of KAST. Winds then shift west to northwest inland after 20z Mon to 00z Tue. This onshore shift will also allow for the return of marine stratus to the coast Monday evening with a 60-80% chance of MVFR/IFR cigs returning south of KTMK between 02-06z Tue.

KPDX AND APPROACHES...VFR conditions expected throughout the period, with low chances (10%) of MVFR cigs after 09z Mon. Northwest winds less than 6 kts, turning west after 21-23z. -03

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.