textproduct: Portland

SYNOPSIS

High pressure will keep the region dry and warm through the weekend, though temperatures ease down a bit after today. Clouds will increase late Sunday ahead of a frontal system, with rain and cooler temperatures returning Sunday night into Monday. Breezy conditions are possible with the front, which could affect outdoor Memorial Day plans.

DISCUSSION...Today through Thursday

Early this Friday morning, the overall pattern remains quiet with broad ridging extending from the northeast Pacific into the Pacific Northwest. Compared with Thursday, the air mass is still warm but the peak heat has passed, and today should come in a few degrees lower for most inland areas. Expect another dry day, with the coast starting cooler under marine stratus while inland valleys warm efficiently.

The dry stretch holds through Saturday and much of Sunday as high pressure remains the primary influence. Temperatures trend slightly downward through the weekend, but remain above late- May averages, generally near 80 today for inland valleys, then settling into the mid to upper 70s Saturday and Sunday. Along the coast, marine stratus will continue to play a larger role in day to day temperatures, keeping highs mainly in the 60s with the potential for slower clearing at times.

Changes arrive late Sunday into early next week as the ridge flattens and flow becomes more progressive. Ensemble guidance continues to show strong agreement that a frontal system pushes into the Pacific Northwest late Sunday night into Monday. Rain chances increase first along the north Oregon and southwest Washington coast late Sunday night, then spread inland Monday morning. While this looks like a beneficial, non-impactful rain event overall, there is still uncertainty in exact onset timing and totals.

Current probabilities for at least 0.50 inches of rain (48 hour totals through early Wednesday morning) remain highest over terrain: roughly 70-90% for the coast and Coast Range and 80-90% for the Cascades. Probabilities drop across the lowlands, with about a 40-60% chance for the Portland/Vancouver metro and southwest Washington lowlands and around a 30-50% chance for the Willamette Valley.

In addition to the rain, Monday may turn breezy as the front moves through. Probabilities favor gusts exceeding 25 mph (around 50-70%), with a lower chance (roughly 20-40%) of gusts exceeding 30 mph. These speeds are not currently suggestive of advisory-level winds, but could be enough to create minor issues for unsecured tents or light outdoor gear.

Behind the front, temperatures cool sharply with highs dropping into the lower to mid 60s across interior lowlands Monday and Tuesday. Showers may linger into Tuesday before the pattern trends closer to seasonal midweek, though there remains uncertainty ties to lingering low-end precipitation chances. ~12

AVIATION

Currently mostly MVFR/IFR status along the coast and VFR conditions inland. Inland terminals will see clear skies and VFR conditions through the period, with increasing north to northwesterly diurnal winds with gusts up to 20 kt possible between 18Z Fri and 06Z Sat. Deteriorated conditions at coastal terminals may improve to MVFR by 18Z Fri (40-60% chance of MVFR). Any improvements will be brief, as CIGs are expected to fall back to IFR conditions by 01-03Z Sat. North to northwesterly winds will increase along the coast by 18Z Fri, bringing gusts of 20-25 kt until around 06Z Sat.

KPDX AND APPROACHES...VFR conditions continue through the period. There is a 10-20% chance of low marine stratus reaching up Columbia River, resulting in MVFR CIGs over the terminal. By 18Z Fri, any low clouds developed over the terminal will clear quickly. Diurnal northwest winds will rise to 5-10 kt by 18z Fri and possibly gust up to 20 kt until 06Z Sat. ~12

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 for northerly wind gusts up to 25-30 kt remain in effect for the waters south of Cape Falcon and for the outer waters north of Cape Falcon beyond 10 NM through 11 PM Friday. Seas 6 to 9 feet are expected across all waters through this weekend. The summer-like pattern is expected to break down Sunday night as a front approaches the waters. This system will return breezy southwesterly winds and a westerly swell that will likely (60-80% chance) build seas above 10 ft by Monday. ~12/10/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ252- 253-271>273.