textproduct: Portland

SYNOPSIS

Warm, dry weather continues today and Sunday under high pressure, with cooler coastal conditions where marine clouds linger. A strong pattern change arrives late Sunday night into Memorial Day with widespread rain, breezier winds, and a notable cool-down. Showers and a few thunderstorms remain possible into Tuesday before the week drier.

DISCUSSION...Today through Friday

Early this Saturday morning, upper-level high pressure remains the main influence across the Pacific Northwest, keeping the storm track displaced north and supporting another dry day. The biggest near-term detail is the onshore component at low levels: that will keep the coast and immediate coastal valleys slower to warm, while inland areas respond more readily to sunshine and downslope warming into the afternoon.

Through Sunday, Expect a continuation of the warm and dry setup with only modest day to day changes. Inland valleys should generally top out in the upper 70s to lower 80s both days, while coastal highs stay about 15-20 degrees cooler (mainly low 60s to low 70s) depending on the reach and persistence of marine stratus and ocean upwelling influences. The Cascades and foothills should land between those two regimes, most often mid 60s to mid 70s. Overall, precipitation remains unlikely through Sunday evening.

Late Sunday night into Monday, confidence is high that the pattern turns much more active as a broad Gulf of Alaska low presses southeastward into the region. Rain becomes widespread on Memorial Day, with a cool, damp feel compared to the weekend. Guidance continues to support 24-hour rainfall totals (roughly 5 AM Monday to 5 AM Tuesday) generally in the 0.25 to 1.00 inch range, with the highest totals favored along the coast, Coast Range, and Cascades. Probabilities for at least 0.25 inch are 70% or higher in many areas, while the odds of 0.50 inch or more drop to around 15-45% in the Willamette Valley but remain much higher (70-90%) for the coast/Coast Range/Cascades. There is also a corridor from Newport north toward Seaside where probabilities for 1.00 inch or more reach roughly 30-50%.

In addition to the rain, Monday looks breezy. Current probabilities favor gusts over 25 mph across much of the forecast areas (around 90%), with gusts over 30 mph more likely along the coast (about 70-90%) than inland (roughly 50-70%). Higher-end gusts around 35 mph remain a lower-probability outcome inland (about 10-30%) but are more plausible at the coast (40-60%). While not currently pointing to advisory-level winds, these speeds could still create issues for canopies, tents, and other unsecured gear. These expected breezy winds will continue to be monitored as confidence for 35 mph gusts have increased compared to the previous forecast.

Thunderstorm potential also bears watching Monday. While instability is not impressive, guidance suggests modest CAPE could be sufficient for a few thunderstorms, and a low-end (15-20%) thunder mention is warranted at this time. Temperatures fall sharply with highs Monday mainly in the mid 50s to mid 60s.

By Tuesday, the low continues southeast with showers lingering and another low-end thunderstorm potential in the afternoon. Some solutions slow the system down, which would shift a portion of the precipitation into Tuesday rather than keeping it concentrated on Monday. Mid to late week trends toward drier weather as a weak high pressure and more zonal flow develop, though temperatures remain on the cool side compared to the weekend warm spell. ~12

With Memorial Day approaching, we remember those who served and are no longer with us. Veterans in crisis or in need of support can contact the Veterans Crisis Line 24/7 by calling 988 and pressing 1 or texting 838255.

AVIATION

Mostly VFR conditions inland and MVFR/IFR conditions along the coast as 11Z Sat. Expect high pressure to continue over the airspace through the TAF period. Coastal terminals will continue under IFR/MVFR conditions through at least 19-21Z Sat, possibly improve to high-end MVFR or VFR through 01-05Z Sun (70-80% chance of VFR), then potentially drop back down to MVFR/IFR CIGs (40-60% chance of MVFR; 20-40% chance of IFR).

For inland terminals, there is a 30-40% chance of MVFR CIGs between 12-17Z Sat, but that will greatly depend on the amount of radiational cooling. Given MVFR CIGs at KKLS and scattered clouds around 3 kft over KPDX, there is moderate to high confidence for some MVFR conditions between the aforementioned time within the Willamette Valley.

North to northwesterly winds will continue through the TAF period. While there has been a brief lull of gusty winds early this morning, expect a return of gustier winds between 16Z Sat and 06Z Sun for the coast and 21Z Sat to 06Z Sun for inland terminals. While most terminals have a chance to see gusts up to 20 kt, coastal terminals could see gusts up to 25 kt.

KPDX AND APPROACHES...VFR through the TAF period, with a 30-40% chance of MVFR CIGs between 12-17Z Sat. Northwesterly winds, with gusts up to 20 kt possible between 21Z Sat and 06Z Sun. ~12

MARINE

High pressure offshore will maintain breezy northerly winds through today. The strongest winds are expected during the afternoon and evening as the surface thermal trough strengthens over the northern CA/southern OR coast. Small Craft Advisories for northerly wind gusts up to 25 kt remain in effect for the waters south of Cape Falcon through 5 AM Sunday. Seas 6 to 8 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 by early Monday morning and a westerly swell that will likely (>80% chance) build seas above 10 ft by Monday afternoon. Additionally, there is a 40-60% chance of wind gusts at or above 34 kt on Monday for the waters north of Cape Foulweather OR. ~12/10

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 5 AM PDT Sunday for PZZ252-253-272- 273.