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

Satellite observations from 21-21:30Z Monday depicted lingering marine stratus along the central Oregon coast with ceilings ranging between 700-2200 feet, bringing continual flight impacts to KONP. Skies have finished clearing out across the rest of northwest OR and southwest WA, resulting in VFR flight conditions at all other terminals.

Similar to last night, expect another southerly marine surge to bring a return of low stratus to the north OR coast and southern Willamette Valley and possibly the central/northern Willamette Valley and Portland metro as well. There is a 60% chance for MVFR ceilings beginning around 09Z Tuesday at KEUG, increasing to a 90% chance by 12Z Tuesday. This stratus deck may also spread northward into KSLE between 12-15Z Tuesday (30-50% chance). Confidence is relatively lower for KUAO, KTTD, KPDX, and KHIO. Probabilities for ceilings below 3000 ft at these TAF sites now peak between 25-45%. If these TAF sites do observe another round of low stratus Tuesday morning, it would most likely hold off until 14-16Z, similar to what was observed Monday morning.

Southerly to southwesterly winds have weakened a bit as of 21Z Monday. A sea breeze front is still expected to push inland between 00-03Z Tuesday, bringing an abrupt shift to westerly winds inland, except northwesterly in the Portland metro.

KPDX AND APPROACHES...Skies should remain mostly clear through at least 06-10Z Tuesday. There is now a 35-45% chance for low stratus with MVFR ceilings below 3000 ft between 10-18Z Tuesday. Light and variable winds under 5 kt are expected to become west to northwest after 01-02Z Tuesday with an incoming sea breeze front. Winds are expected to become light again around 06Z Tuesday. -23

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.