textproduct: Portland

SYNOPSIS

A few showers and isolated thunderstorms may linger early this morning, mainly over portions of northwest Oregon and southwest Washington, before activity gradually diminishes. Cooler and less humid conditions are expected today as onshore flow strengthens, though inland areas will still be warm this afternoon. Dry weather is favored Friday, followed by a cooler weekend with increased marine influence and a slight chance of light showers along the coast Saturday.

DISCUSSION...Now through Wednesday

The weather pattern is in transition this morning as the hot and more convectively active setup from Wednesday gives way to a cooler marine-influenced regime. An upper low offshore continues to influence the region early today, and while some residual showers or isolated thunderstorms may persist around daybreak, the overall trend will be toward weakening instability and decreasing coverage through the morning hours. Any remaining thunderstorm risk should diminish steadily through the morning, with most locations turning dry by afternoon

Today, increased onshore flow and a cooler air mass will support lower afternoon highs, while humidity levels gradually increase as well. Inland locations are still expected to warm into the mid to upper 80s this afternoon, so conditions will remain seasonably warm even as the recent heat event comes to an end. Coastal areas should hold in the 60s, with a more noticeable marine influence returning.

Friday appears relatively similar in terms of the overall upper level pattern, with dry weather continuing and temperatures not changing much from today. Looking farther ahead, a trough dropping south from the Gulf of Alaska will reinforce onshore flow heading into the weekend. That should bring a more noticeable cooling trend, more persistent night and morning cloud cover, and temperatures closer to seasonal normals by Saturday and Sunday. Inland highs this weekend should generally settle into the upper 70s to lower 80s, while overnight lows fall back into the 50s. Precipitation chances remain limited overall, but there is still a low-end signal for light showers along the coast on Saturday. Ensemble guidance generally supports this more seasonable pattern continuing into early next week, with no strong signal for a return to significant heat. ~12

AVIATION...Through 12Z Friday

Radar and satellite observations as of 10Z Thu shows dwindling rain showers over the central and northern Willamette Valley and Portland metro. While thunderstorms have come to an end as of 10Z Thu, thunderstorm development remains possible over southwest Washington until 15Z Thu, diminishing thereafter.

Inland, CIGs continue to gradually lower, liking bringing low- end VFR/high-end MVFR CIGs to terminals by 12-14Z Thu. Expect any deteriorated CIGs inland to scattering out and lifting to VFR by 18-19Z Thu. Along the coast, current IFR/MVFR CIGs are expected to persist through the morning, then likely lifting back to VFR by 20-22Z Thu. By 03-04Z Fri, CIGs will begin to deteriorate back to IFR/MVFR. Guidance suggests a 30-50% chance of MVFR CIGs and 10-20% chance of IFR CIGs around 03-04Z Fri to increase to 60-80% chance of MVFR CIGs and 20-40% chance of IFR CIGs by 09-10Z Fri. Otherwise, expect winds of 5-10 kt through the TAF period, southerly to westerly along the coast and southerly shifting to northwesterly by the afternoon for inland terminals.

KPDX AND APPROACHES...Thunderstorm chances of 15% will increase to below 10% by 15Z Thu. Current VFR CIGs will likely lower to high-end MVFR by 13-14Z Thu, then scatter out and lift to VFR by 18-19Z Thu. Light northwest winds increase to around 6-8 kt by Fri afternoon. ~12

MARINE

Buoy observations as of 3 AM Thursday show southerly winds occurring over the coastal waters around 10-15 kt with seas around 6 ft at 8 to 10 seconds. Expect these southerly winds to decrease further through today. Seas are expected to hold steady with minimal change.

Seas decrease to 4 to 5 ft on Friday with light southwest winds in place, resulting in benign conditions. Seas then increase to 6 to 7 ft on Saturday as southerly winds ramp up with the passage of a cold front. This front will bring wind gusts upwards of 20-25 kt and chances for rain showers. Given the increase in winds and seas, conditions are expected to become hazardous to small craft. Winds and seas then decrease on Sunday in the wake of the cold front. ~12/23

PQR WATCHES/WARNINGS/ADVISORIES

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