textproduct: Portland

SYNOPSIS

Dry and warm weather is expected across the region through the weekend with high pressure over the Northeast Pacific spreading east over the Pacific NW. Rain and cooler temperatures return to the area late Sunday into early next week, which could impact any outdoor Memorial Day plans.

DISCUSSION...Wednesday afternoon through Tuesday

Visible satellite imagery early Wednesday afternoon shows mostly clear skies across NW OR with dissipating stratus across SW WA as high pressure over the eastern Pacific expands east over the West Coast. Temperatures today will be similar to yesterday with inland highs in the low 70s and mid 50s to low 60s along the coast. Dry weather continues through the weekend as the area generally remains under high pressure.

Winds turn weakly offshore by Thursday morning as the high pressure peaks over the area and a weak surface thermal trough builds along the N CA and S OR coast. Some locations in the Willamette Valley may see stratus again Thursday morning, but drier air from the offshore winds will limit widespread expansion. This pattern continues into Friday, allowing temperatures to warm to around 10-15 degrees above daily normals for Thursday and Friday. Expect daytime temperatures to peak in the low to mid 80s for inland valleys and 60s along the coast. There is a 35-45% chance for Moderate Heat Risk in the Portland metro area and Tualatin Valley and a 10-25% chance in the rest of the interior valleys on Thursday. These chances fall to 5-15% on Friday.

A weather system pushing through Canada over the weekend will break down the high pressure over the PacNW and lead to more zonal flow. Temperatures will fall a few degrees but still remain above normal, peaking in the mid to upper 70s both Saturday and Sunday for inland valleys. There is much higher agreement that Sunday will remain mainly dry and warm, though could begin to see increasing cloud cover ahead of an approaching weather system.

About 85-90% of ensemble members from the GFS, Euro, and Canadian ensembles indicate the weather system will push into the PacNW sometime late Sunday night into Monday bringing shower chances through Tuesday. Some uncertainty still remains in general timing of rain as well as rain totals, but latest consensus is that rain will hold off until at least late Sunday night along the far N OR and SW WA coast, then spread southeast Monday morning. Confidence is high that this will be non- impactful rain. The NBM 90th percentile (only 10% chance of occurring) for 48 hour rain totals through 5 AM Wednesday indicates 0.5-0.95 inch for the Willamette Valley, 0.8-1.6 inches along the coast and Coast Range, and 1-1.5 inches along the Cascades. When looking at the probability of reaching or exceeding 0.5 inch for the same time period, there's a 10-20% chance for the Willamette Valley, 20-40% for the Portland and Vancouver metro area and SW WA lowlands, 30-60% for the coast and Coast Range, and 45-60% for the Cascades. Temperatures will also drop substantially for Monday and Tuesday with high temperatures in the mid 60s for the interior lowlands. -03

AVIATION

Satellite imagery as of late Wednesday morning depicts MVFR stratus continuing to break out across the region. By 22-23z Wed, an upper level ridge offshore will support a return of northerly winds and VFR conditions with a FEW/SCT high clouds across the region, lasting through the end of the TAF period. North-northwesterly gusts up to 20-25 kt along the coast (strongest near KONP) through 03-04z Thu. For the Willamette Valley, north winds generally 10-15 kt except under 10 kt across the Portland/Vancouver Metro Area. Winds ease overnight. There remains a 15-30% chance for MVFR stratus returning along the coast at any given hour between 12-18z Thu. Otherwise, VFR conditions prevail.

KPDX AND APPROACHES...VFR conditions through the TAF period. Northwesterly winds 5-10 kt this afternoon, weakening below 5 kt tonight. -10

MARINE

High pressure offshore will maintain breezy northerly winds through the end of the week. The strongest winds are expected during the afternoon and evening periods as the surface thermal trough strengthens over the northern CA/southern OR coast. Small Craft Advisories remain in effect for the waters south of Cape Falcon through early Friday morning for northerly wind gusts up to 25 kt. Will note that there may be a brief lull in the winds between 5-11 AM Thursday for the inner waters zones (from the coast to 10 NM offshore) before increasing again tomorrow afternoon. For the outer waters north of Cape Falcon, Small Craft Advisories remain are in effect through tonight, and again Thursday evening. A Small Craft Advisory has also been issued for the Columbia River Bar between 7 AM-12 PM Thursday for a strong ebb current bringing seas up to 7 ft along the Main Channel. Seas 6 to 9 feet expected across all waters through this weekend. The summer-like pattern is likely to break down Sunday night as a front approaches the waters and returns southwesterly winds. -10/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 7 AM to noon PDT Thursday for PZZ210.

Small Craft Advisory until 5 AM PDT Friday for PZZ252-272.

Small Craft Advisory until 5 AM PDT Friday for PZZ253-273.

Small Craft Advisory until 5 AM PDT Thursday for PZZ271.

Small Craft Advisory from 5 PM Thursday to 5 AM PDT Friday for PZZ271.