textproduct: Portland

SYNOPSIS

Warm and dry conditions expected to continue through the week, with a brief cooldown likely on Wednesday as clouds and onshore flow increase. Precipitation chances remain low through the weekend, but there are indications of increasing chances for rain early next week (though chances remain low at this time).

DISCUSSION...Today through Monday

Onshore flow continues with another day of near average temperatures expected. A few morning clouds will give way to mostly sunny skies as highs warm back into the lower to mid-80s across the interior lowlands. Slightly cooler conditions are expected on Wednesday as the upper level pattern shifts from zonal flow to more troughing. Broad upper level troughing over British Columbia this evening becomes a bit more organized as it drops south into Washington and Oregon. This pattern typically corresponds with a deepening of the marine layer allowing for marine stratus to push inland by Wed morning. Would not be surprised for the coast to see some drizzle Wed morning as well. With the deeper cloud layer lingering into the afternoon, temperatures will be slower to warm resulting in highs reaching into the mid to upper 70s in southwest WA and Portland metro area, while temps in the southern Willamette Valley are more likely to warm into the lower 80s. Any rain or thunderstorm chances are likely to stay across portions of the northern half of WA.

Beginning to see a bit more agreement among the models and their ensembles for later in the week as the upper level pattern is trending toward broad upper level troughing. The potential range of afternoon high temperatures from the NBM for Thursday and Friday has generally consolidated into the lower to mid-80s, retuning the likelihood of near to slightly above average conditions for mid- August. More uncertainty into the weekend, but ensembles are suggesting weak upper level ridging may nudge back into the Pacific NW as low pressure deepens the upper trough offshore. This could result in a slight warming trend, though models suggest there is only around a 10% or less chance of exceeding 90 degrees. Shortwave troughs within the more southwesterly flow aloft along with some increasing monsoonal moisture will bring chances for convection along the Cascade crests for Saturday afternoon.

The question then turns to the possibility of rain early next week. But, the probability for measurable precipitation remains low (20% or less) across the area next Monday. Cluster analysis of 500 mb heights shows a wide range of the strength and depth to the upper level trough offshore, while around 10-15% of ensembles show the potential for any substantial rainfall across the area. /DH

AVIATION...Through 12Z Wed

Westerly flow aloft continues with predominately VFR conditions expected inland. Marine stratus continues to fill in along the coast early this morning returning low-end MVFR to IFR CIGs. Stratus is expected to persist at coastal terminals through 18-21z, lingering longest near KAST. Onshore flow may also push stratus up the lower Columbia River Valley, with lower chances (10-20%) of reaching the Portland Metro area today. VFR conditions with clear skies prevail for Willamette Valley terminals through at least 06-08z Wednesday. A stronger marine push will be possible for Wed morning as upper level troughing allows for deepening of the marine layer. North to northwest winds continue across the area, increasing to around 8-12 kt in the afternoon.

KPDX AND APPROACHES...Predominately VFR with clear skies through at least 06-08z Wed. There is a 10-20% chance for MVFR CIGs at any given hour between 12-17z Tue. Northwest winds increase to 8-10 kt after 18z Tue. /DH

MARINE

High pressure offshore will continue to support northerly winds and fairly benign conditions across the coastal waters through the week and into the weekend. Winds are expected to ease today, trending toward 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. /DH

PQR WATCHES/WARNINGS/ADVISORIES

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