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 06Z Wed

Satellite imagery as of late Monday evening depicts marine stratus filling in along the coast, returning low-end MVFR CIGs (1-2 kft) to KAST. Expect MVFR CIGs to gradually make its way to KONP in the next hour or so. High confidence for IFR/MVFR CIGs tonight along the coast as stratus holds. Increasing onshore flow may also push stratus up the Lower Columbia River Valley and could reach the Portland Metro Area later this morning. The onshore push doesn't look as strong as yesterday, but there is still a 15-20% chance for MVFR CIGs at any given hour between 12-17z Tue for eastern Portland Metro terminals. Otherwise, VFR conditions with clear skies prevail for Willamette Valley terminals through the TAF period. Variable winds under 5 kt tonight, becoming north- northwesterly and increasing to 7-11 kt at any given terminal after 18-21z Tue.

KPDX AND APPROACHES...Predominately VFR with clear skies through the TAF period. There is a 15-20% chance for MVFR CIGs at any given hour between 12-17z Tue. Northwest winds 3-4 kt tonight increasing to 8- 10 kt after 18z Tue. -10

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.