textproduct: Portland

SYNOPSIS

High pressure will result in dry and warm conditions across the area today. 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 in the afternoon. Conditions trend slightly drier over the weekend, but there remains chances for lingering showers.

LONG TERM...Wednesday through Sunday

Wednesday into Thursday continues to be far more impactful in terms of precipitation as the majority of ensemble members continue to show a second, much deeper upper-level trough dropping down out of the Gulf of Alaska and into the Pacific Northwest. The associated surface front with this more robust system swings through on Wednesday, bringing widespread rain, cooler temperatures, and breezier 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 35-50% for these higher terrain features, and 5-15% along the I-5 corridor. It should be noted that the primary cause for the uncertainty is the exact track of this low. While most ensembles show the center of the low coming on shore south of the Olympic Peninsula and then moving eastward, some solutions do have this low slowing down and hugging the OR/WA coast before pushing inland near the mouth of the Columbia River Bar. A more southerly track could result in precipitation totals being slightly less than currently forecasted.

Thursday afternoon to Saturday, the upper-level trough remains over the Pacific Northwest and we transition into a post-frontal environment with lingering showers over the CWA. 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. -42/10

AVIATION...Through 18z Tuesday

VFR conditions expected to remain in place across the airspace into this evening at coastal terminals, and into tonight inland. Largely clear skies will persist through today, with winds rising to 5-10 kt inland and to 8-12 kt along the coast. Weakening offshore flow early will see east winds through the Columbia Gorge and north winds along the Willamette Valley begin to shift out of the west to southwest as onshore flow is re-established by this afternoon.

This evening and tonight, an onshore push will see 70-80% chances of IFR cigs at coastal terminals after 02-04z Tue, and 60-80% chances of MVFR cigs at inland terminals after 10-12z Tue, increasing overnight from south to north. Winds shift out of the south to southwest this evening and overnight ahead of an approaching frontal system over the Northeast Pacific.

KPDX AND APPROACHES...VFR conditions expected into tonight. Northwest winds of 5-10 kt shift southerly this evening as a marine push brings 70-80% chance of MVFR cigs after 12z Tue. -36

MARINE

Weak ridging over the region will maintain north/northwest winds through tonight. Thermal troughing along the coast will result in strengthening near-shore winds this afternoon with gusts to 25 kt within 10-20 NM north of Cape Falcon and including the Columbia River Bar. Will maintain the current Small Craft Advisory from 2 PM to 8 PM PDT this afternoon and evening. Largely wind- driven seas will persist at 4-6 ft during this period.

On Tuesday, winds become southerly as the start of a widespread pattern change is expected. A series of robust troughs, diving out of the Gulf of Alaska and subsequently moving eastward over the Pac NW will bring about increasing winds and building seas across all waters. By Tuesday evening/Wednesday morning, a robust frontal system will move across all forecast zones. This frontal system will result in southerly wind gusts up to 40 kt as well as seas building towards 10-12 ft across all waters. Therefore, have issued a Gale Watch for all waters as well as the Columbia River Bar starting Tuesday evening through at least Wednesday evening. There is around a 20% chance for gusts up to 50 kt through the Gale Watch time frame, with highest probability within the near- shore waters. Also, there is a less than 10% chance at this time for significant wave heights to reach 15 ft. Behind this system, winds and seas are expected to ease below 15 kt and 8 ft for the remainder of the week and into the weekend. -42/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory from 2 PM this afternoon to 8 PM PDT this evening for PZZ210-251.

Gale Watch from Tuesday evening through Wednesday evening for PZZ210-251>253-271>273.