textproduct: Portland

SYNOPSIS

High pressure aloft remains firmly in place over the eastern Pacific and Pacific Northwest, supporting a warm (still above average) and mostly dry pattern through midweek. Night and morning marine clouds will continue to visit the coast and occasionally push inland through gaps, but daytime clearing should remain common. By Friday into Saturday, the ridge weakens as a disturbance brushes the region, bringing the next chance for rain, though exact timing and where rain is most likely are still not locked in. Drier weather is favored to return late in the weekend as ridging attempts to rebuild.

DISCUSSION...Now through Sunday

This afternoons weather is being driven more by a low level pattern than anything aloft: onshore flow (southwesterly) is feeding marine air and low stratus into the coast, while inland areas have cleared from low stratus and will remain warm under persistent ridging. While skies at Astoria have cleared, expect most coastal areas to lean cloudier overall with occasional mist or drizzle near the beaches. The interior should stay dry with filtered sun and mild to warm temperatures. Highs through the interior valleys will generally run in the 70s, while the coast and higher terrain remain cooler, mainly in the 60s. Marine stratus is most likely to expand inland again tonight into early Tuesday, then pull back toward the coast during the afternoon.

Tuesday through Thursday, not much changes as the ridge holds over the PNW. Temperatures wont be as hot as Sundays (yesterday) record-setting warmth, but will still run around 5 to 10 degrees above average for many inland locations. Even so, expect cooler mornings as coastal clouds move inland overnight and retreat by afternoon, but this does not appear to be a sustained "May Gray" setup. Most locations remain rain free during this stretch.

Confidence drops late in the week as ensembles suggest a shortwave riding over the top of the ridge and nudging it weaker. That feature is the best opportunity for a broader increase in rain chances, most likely sometime between Friday morning and Saturday afternoon. Current guidance favors the highest odds within the interior of southwest Washington, along the coast north of Newport OR, and over higher terrain (including the Coast Range and Cascades). Moisture looks limited at this time, so amounts, where rain occurs, still appear light (generally less than a tenth of an inch).

Looking beyond that system, most solutions rebuild upper level ridging, which would bring a return to dry and warmer than normal weather late in the weekend into early next week. Details are still uncertain on exactly where the ridge axis sets up, and that placement will matter for how quickly we dry out and how warm inland temperatures rebound. ~12

AVIATION

As of 05z Tue, marine stratus has reformed along the coast with an onshore marine surge pushing the marine stratus inland through Coast Range gaps in central OR as well as along the Columbia River. Satellite imagery show the marine moisture is also causing back building stratus to form along the western Cascade foothills, which will then slowly continue building west through the night. Current MVFR conditions along the coast will become IFR after 06-08z Tue with drops to IFR cigs possible through 14z Tue. Expecting cigs at most inland terminals to become MVFR, most likely sometime between 06-12z Tue. Inland terminals should improve to VFR conditions by 18-21z Tue. Coastal terminals likely to remain MVFR/IFR through most of the TAF period, though could see a few hours of improvement to VFR at some point between 19-23z Tue.

Winds generally southwesterly along the coast and southerly inland, though more variable around the Portland metro terminals. Winds shift more westerly along the coast and northerly inland after 18z Tue, generally less than 10 kts.

KPDX AND APPROACHES...Marine stratus is forming around Portland area terminals as of 05z Tue. Expect cigs to drop to MVFR less than 3000 ft sometime between 06-12z Tue. Cigs may initially fluctuate between low end VFR and MVFR before fully settling into MVFR by 12-14z Tue. Expect conditions to improve to VFR by 17-19z Tue. Northerly winds around 7 kts will become light and variable between 06-09z Tue then shifting northwesterly after 18z Tue. -03

MARINE

A southerly surge will bring persistent low stratus through Wednesday with chances for fog and/or drizzle during the overnight and morning hours each day. Southerly winds persist over the coastal waters Monday afternoon, but have weakened to around 10-15 kt. South winds will weaken slightly more late Monday night into Tuesday morning before becoming westerly Tuesday afternoon.

Winds look to turn northerly late Wednesday through Thursday evening. A weak system moving onshore Friday into Saturday will favor a return of southerly flow and increased chances for rain showers, before high pressure rebuilds later this weekend and northerly flow strengthens. Northerly winds may become hazardous to small craft late Saturday into Sunday with gusts up to 20-25 kt. The strongest northerly winds are expected Sunday afternoon and evening when there is a 60-80% chance for max wind gusts over 21 kt. The highest probabilities are south of Cape Falcon. Seas are not expected to change much now through the upcoming weekend, generally ranging between 4 and 7 ft with a persistent westerly to northwesterly swell. -23

PQR WATCHES/WARNINGS/ADVISORIES

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