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

Satellite imagery and terminal observations as of late Thursday morning depicts BKN/OVC MVFR CIGs across northwest Oregon. As daytime heating progresses, will see increased mixing which should break up stratus and improve conditions to predominately VFR for most terminals. There is some uncertainty with potential clearing at KONP. Onshore flow and moist conditions may keep KONP within MVFR CIGs throughout the day, however, there is a 50-70% chance for some very brief improvements to VFR between 21z Thu-00z Fri at KONP. By the evening after 00-03z Fri, there high confidence that IFR/MVFR marine stratus will return along the coast. For inland locations, VFR conditions prevail throughout the TAF period with high clouds. Will note that there is a 20-30% chance for MVFR stratus across the Willamette Valley at any given hour between 10- 18z Fri as the low level atmosphere moistens. Winds generally light and west-northwesterly, except for increasing southwesterly winds at KEUG this evening around 10 kt.

KPDX AND APPROACHES...MVFR CIGs through 19-20z Fri. Afterwards, increased mixing will support VFR conditions through the rest of the TAF period. Low-end VFR stratus after 10-12z Fri with a 15-25% chance for MVFR CIGs at any given hour between 12-18z Fri. -10

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.