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 through Thursday, strongest in the afternoon and along the Central Columbia River Gorge and Upper Hood River Valley. Low chances for light showers arrive Thursday night through Saturday, but conditions most likely remain dry, along with 5-10% chance for evening thunderstorms along the Cascades. Seasonable weather continues late this weekend into early next week.

DISCUSSION...Tonight through Monday

The overall forecast remains stagnant with little change to the forecast as predominately dry and warm conditions continue through the week with minimal impacts. The synoptic pattern through the mid-week remains stagnant as a col will continue to dominate the Pac NW. This col continues to be defined by a high over the Great Basin and a low within the eastern Pacific. While there is a mirrored high over the Gulf of Alaska and mirrored low over the central provinces of Canada, these two systems are not as impactful as the ones closer to CONUS. Overall, this pattern will support continued onshore flow at the surface, which will maintain 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 approaching 30-35 mph through the evening.

The majority of ensemble members are in agreement that aforementioned upper-level ridging over the Rockies and Great Basin will start to dominate on Thursday and will result in a brief warm up across the CWA. However, that warm-up will likely be short-lived as ensemble guidance continues to show the eastern Pacific low moves northeast-ward Thursday through Saturday. This will bring a return of slightly cooler temperatures as well as a southerly wind shift. This southeasterly flow is a favorable pattern for precipitation as well as thunderstorms. However, the overall atmosphere continues to remain dry, thereby limiting the potential for any precipitation. But, models are starting to show some general, elevated instability from Thursday through Saturday. So, this will bear continue scrutiny through the remainder of the week. It should be noted, that there remains a lot of uncertainty as to the exact timing of the Pacific low, as some ensembles have the low moving into the region as early as Thursday evening, while others push it out around 24 hours (Friday evening). To summarize the summary, there is a 5-10% chance for elevated thunderstorms for the Cascades from Thursday through Saturday, starting in the late afternoon through the overnight hours each day.

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 a fair amount of uncertainty with the exact magnitude and placement of the late weekend/early next week trough. However, this would suggest that onshore flow continues across the region resulting in seasonable temperatures for late August. /42-10

AVIATION...Through 06z Thursday

VFR conditions inland with MVFR stratus covering the coastal areas. Conditions are expected to follow a similar pattern to the previous night with stratus moving up the Columbia river into the Portland metro after 12z. Stratus is a few hundred feet higher than last night sitting between 1000-1500 feet. Expecting mainly MVFR CIGs with this cloud layer but could see brief drops below 1000 feet. Expect improvement back to VFR for inland terminals between 16-18z and early afternoon along the coast. Light overnight winds becoming northwest 5-10 kt.

KPDX AND APPROACHES...VFR conditions with mostly clear skies. MVFR/IFR stratus expected to return after 12z Wed, improving to VFR once again by 17-19z Wed. Northwesterly winds 4-7 kt. -19/03

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 and evening gusts up to 15-20 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 with a 30-50% chance of northerly wind gusts exceeding 21 kts in the afternoon and evening hours south of Cape Falcon. 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. -03/10

PQR WATCHES/WARNINGS/ADVISORIES

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