textproduct: Portland

SYNOPSIS

Warm and dry conditions expected through much of the week with morning clouds and afternoon clearing. Daytime highs are expected to be in the 80s through the week. Winds generally out of the west to northwest, strongest in the afternoon and along the Central Columbia River Gorge and Upper Hood River Valley. Spotty chances for light showers arrive Friday night into Saturday, but conditions most likely remain dry. Seasonable weather continues late this weekend into early next week.

DISCUSSION...Today through Monday

Little change to the forecast as predominately dry and warm conditions continue through the week with minimal impacts. The large-scale pattern remains stagnant through the period, with broad and relatively flat upper-level ridging over the Rockies and Great Basin, and broad upper-level troughing over the northeast Pacific. This pattern will support continued onshore flow, maintaining near- normal daily high temperatures in the 80s within inland valleys and 60s along the coast, and overnight lows in the 50s across the region. With moist air flowing into the region, each night will be characterized by marine stratus along the coast with some stratus filtering into the I-5 corridor. These clouds should clear out each afternoon as daytime heating progresses. Expect light winds from the west/northwest for most places, peaking each afternoon. An exception would be the Central Columbia River Gorge and Hood River Valley, where west winds will be strongest with gusts to 25-35 mph this afternoon. Chances for wind gusts exceeding 35 mph today along the Central Gorge are around 30-50%.

The majority of ensemble members are in agreement that upper- level ridging over the Rockies and Great Basin will build late in the workweek, which would favor a brief warm-up on Thursday. However, that warm-up will likely be short-lived as ensemble guidance continues to show the upper-level trough over the northeast Pacific shifting onshore Friday into the weekend, resulting in slightly cooler temperatures and winds coming from the south/southwest. There remains spotty chances (10-25%) for showers across portions of the Coast Range and Cascades, but the overall airmass will remain too dry to support accumulating rainfall from a weak front. Late this weekend into early next week, the trough weakens and most ensemble members suggest a return of zonal flow before another upper-level trough drops down from the Gulf of Alaska and approaches British Columbia. At this point, there still remains uncertainty with the exact magnitude and placement of the trough. However, this would suggest that onshore flow continues across the region with seasonable temperatures for late August. -10

AVIATION...Through 12z Wednesday

Satellite imagery and terminal observations as of early Tuesday morning depicts marine stratus along the coast bringing LIFR/IFR conditions to KAST and KONP. This stratus is pushing through gaps in the Coast Range and up the Lower Columbia River, and is expected to reach the Portland Metro Area by 12-14z Tue. Observations along the coast and the Cowlitz Valley (KKLS) show the base of the stratus deck around 400-800 ft, so expect IFR conditions at KPDX/KTTD once the stratus arrives. Low confidence for stratus making it into the central/southern Willamette Valley, as guidance suggests a 15-25% chance for IFR/MVFR CIGs at any given hour between 12-17z Tue.

High confidence for stratus dissipating from the Willamette Valley after 17-18z Tue, returning VFR conditions through the rest of the TAF period. Along the coast, there is a 30-50% chance for brief improvement to VFR at any given hour between 21z Tue-00z Wed before IFR/MVFR stratus returns in the evening. Westerly to northwesterly winds across all terminals around 4-8 kt, peaking this afternoon with gusts up to 18 kt along the coast.

KPDX AND APPROACHES...IFR stratus arriving around 12-13z Tue and lasting through 17-18z Tue. After 18z Tue, daytime heating will dissipate stratus and return VFR conditions through the rest of the TAF period. Northwesterly winds 4-7 kt. -10

MARINE

A largely stagnant pattern continues through much of the week with high pressure offshore supporting northerly to northwesterly winds of 8-15 kt and afternoon gusts up to 20 kt. Weak low pressure moving over the northeast Pacific Friday into the weekend will shift winds out of the south to southwest across the waters, but chances for gusts exceeding 21 kt remain low, only 5% or less. High pressure and northerly winds return by Sunday. Seas of 3-6 ft persist through the period. Increasing periods of 12-14 sec today and Wednesday may result in a moderate risk for sneaker waves along the coast. Caution should be used when in or near the water. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.