textproduct: Portland

SYNOPSIS

Warm and dry conditions continue through the upcoming week as temperatures moderate towards August normals. Onshore flow will keep smoke east of the Cascades, while precipitation chances remain very low through the end of the week. Temperatures may trend warmer late this week as a ridge of high pressure develops offshore. Increasing potential for afternoon convection over the central OR Cascades Friday into the weekend.

DISCUSSION...Today through Sunday

Fairly typical summer weather will continue early this week as near average temperatures are expected today and Tuesday. This is in part due to zonal flow aloft and onshore flow in the lower levels. Relatively shallow marine stratus at the coast will retreat, giving way to mostly sunny skies this afternoon, while a brief period of clouds will be possible this morning up the lower Columbia River Valley into the Portland metro area. Otherwise, mostly sunny skies will allow afternoon temperatures to warm into the lower to mid-80s for interior lowlands, and into the mid-60s to low 70s at the coast. Expect similar conditions on Tuesday.

By Wednesday, there is increasing confidence for upper level troughing dropping out of British Columbia into Washington and Oregon. Model forecast soundings are showing a deepening of the marine layer which would allow for deeper stratus to push into SW Washington and the northern Willamette Valley, as well as the potential for squeezing out some drizzle at the coast. This would also allow for afternoon temperatures to drop a few degrees, depending on how long morning clouds linger. Still some uncertainty late in the week in daytime high temperatures as model spread remains relatively large Thursday and Friday. If troughing were to linger around, cooler (or near average) temperatures would be more likely, but a warming trend is also possible with highs returning into the mid to upper 80s, with at least a 25% chance of reaching 90 degrees on Friday. Cluster analysis of the ensembles indicates the potential for upper level ridging to build offshore with varying degrees of troughing or upper level low pressure developing near central California. This feature is also bringing the potential for more convective weather developing near the central OR Cascade crest both Friday and Saturday afternoons with the northward push of some monsoonal moisture. Temperatures are likely to persist near to slightly above normal into next weekend, with warm and dry conditions likely. /DH

AVIATION...Through 12Z Tue

Dry, westerly flow aloft continues with marine stratus filling in along the coast and up the lower Columbia River Valley. High confidence for low-end MVFR CIGs through 20z Monday, with chances for IFR CIGs at around 40-50% between 12-18z this morning. Confidence for stratus developing at KONP increases after 10z early this morning with IFR CIGs likely between 12-16z, followed by improvement back to VFR as clouds scatter out by 18z.

Given that stratus as already reached the KKLS area early this morning, Portland Metro terminals, including KPDX and KTTD, could see MVFR CIGs between 13-16z Mon. As daytime heating progresses, stratus will gradually dissipate, returning VFR conditions to the Portland Metro after 16z Mon and after 19-21z Mon along the coast. For the rest of the terminals in the Willamette Valley, VFR conditions with clear skies prevail through the TAF period. North to northwesterly winds increase to 10-15 kt in the afternoon and evening with gusts up to 25 kt along the coast and up to 20 kt inland.

KPDX AND APPROACHES...Predominately VFR conditions with clear skies expected through the TAF period, except for a period of brief stratus between 13-16z this morning. During this time, there is a 40-60% chance for MVFR CIGs across the eastern Portland Metro. Northwest winds 4-6 kt increase to around 10-12 kt with gusts up to 20 kt by 00z Tue. /DH

MARINE

High pressure offshore will maintain northerly winds through much of next week. Surface pressure gradients tighten again this afternoon with gusts up to 25 kt possible south of Cape Foulweather through this evening. Will maintain the Small Craft Advisory in effect today. Winds look to ease slightly on Tuesday with much lower chances (30%) of wind gusts exceeding 21 kt. Similar conditions persist through late in the week. Wind driven seas are expected to remain around 3 to 6 ft through the week. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from noon today to 11 PM PDT this evening for PZZ253.

Small Craft Advisory from 3 PM this afternoon to 11 PM PDT this evening for PZZ273.