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 trend slightly warmer towards the end of the week as a ridge of high pressure develops offshore. Increasing potential for afternoon convection over the central OR Cascades Friday into the weekend.

DISCUSSION...Tonight through Sunday

Fairly typical summer weather continues this week as near average temperatures are expected through Tuesday. This is in part due to zonal flow aloft and onshore flow in the lower levels. Shallow marine stratus is expected to return overnight along the coast and push inland along the Columbia River towards the Portland/Vancouver Metro area. Clear and sunny skies are expected to return on Tuesday, with a near repeat of Monday's conditions.

For Wednesday, there is increasing confidence that an upper level pattern change will occur as a broad upper level trough will move southward 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 some aggressive drizzle along the coast. This would result in daytime highs for inland valleys to warm into the upper 70s to low 80s, with highs in the 60s along the coast and the 70s for the Cascades. Looking towards the latter part of this week, some uncertainty within the models and their ensembles remain. Daytime high temperature spread remains relatively large Thursday and Friday as guidance is split between the mid-week trough lingering or a return of zonal flow in the upper levels of the atmosphere. If troughing were to linger, cooler (or near average) temperatures would be more likely, but if the more zonal flow pattern develops, a warming trend would be more likely with highs returning into the mid to upper 80s, with at least a 25% chance of reaching 90 degrees on Friday and continuing through Sunday.

500 mb 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 (5-10% chance) 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. /42-DH

AVIATION...Through 00Z Wed

Westerly flow aloft continues as we remain in a zonal pattern through the TAF period. As of 21Z Mon, marine stratus has receded greatly, now well off the coastline from KTMK southward but still lingering in the mouth of the Columbia River. Expect continual burnoff of marine stratus, resulting in KAST likely improving back to VFR by 22-23Z Mon (60-80% chance of VFR by 22-23Z Mon).

Looking ahead, Willamette Valley terminals will stay VFR through the TAF period, with the exception of potential marine stratus bringing a 20-30% chance of MVFR CIGs between 12-18Z Tue for terminals around the Portland Metro. Additionally, there is a 35-50% chance of MVFR CIGs at KKLS beginning around 11Z Tue. As for coastal terminals, another marine stratus push will bring a mix of MVFR/IFR/LIFR conditions between 03-18Z Tue. Guidance suggests majority of this time range to consist of a 70-90% chance of MVFR, 40-60% chance of IFR, and 20-40% chance of LIFR conditions (highest to lowest chances from KAST to KONP). Otherwise, expect north to northwesterly winds of 10-15 kt with gusts up to 25 kt along the coast and up to 20 kt inland this afternoon to weaken into late this evening. Similar winds expected tomorrow by 18-21Z Tue.

KPDX AND APPROACHES...VFR conditions with clear skies through the TAF period. However, there is a 20-30% chance of MVFR CIGs between 12-18Z Tue. Northwest winds around 9-12 kt with gusts up to 20 kt this afternoon will weaken by 06-08Z Tue. Similar winds expected tomorrow by 18-21Z Tue. ~12

MARINE

High pressure offshore will continue to support northerly winds through much of the week. Surface pressure gradients this afternoon may result in wind gusts up to 21 kt south of Cape Foulweather through this evening. The Small Craft Advisory remains in effect until 11 PM Mon. Winds will ease on Tuesday with much lower chances (less than 10%) 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. ~12/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ253.

Small Craft Advisory until 11 PM PDT this evening for PZZ273.