textproduct: Portland

SYNOPSIS

Warm and dry weather continues through Sunday under high pressure, with relatively cooler coastal conditions where marine clouds linger. A notable pattern change arrives late Sunday night/early Monday morning, which will bring widespread rain, breezier winds, and a notable cool-down. Showers and a few thunderstorms remain possible into Tuesday, with a warming and drying trend expected through the end of next week.

DISCUSSION...Tonight through Friday

Marine clouds expected to return tonight as onshore flow will continue under an upper level high pressure system. Through Sunday, expect warm and dry conditions to continue as the overall synoptic setup remains rather static. Daytime highs look to be the warmest for the week on Sunday with inland valleys in the upper 70s to lower 80s, while coastal highs stay about 10-20 degrees cooler, mainly low 60s to low 70s. The Cascades and foothills should land between those two regimes, with daytime highs in the mid 60s to mid 70s. It should be noted that the expansive marine stratus this morning is not expected to be as widespread tonight. However, if the reach and persistence of marine stratus is similar or greater than today, then that could easily keep daytime highs 5-10 degrees cooler than the current forecast. Overall, precipitation remains unlikely through Sunday evening, but could see some "aggressive drizzle" along the coast at times.

Late Sunday night into Monday, a significant pattern change is expected for the Pac NW as a broad, Gulf of Alaska low dives southeastward into the region. This will bring widespread rain and cloud cover across the CWA for Memorial Day. 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 60-90%, while the chances of 0.50 inch or more drop to around 5-35% in the Willamette Valley but remain much higher around 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 widespread rain, Monday looks breezy. Current probabilities favor gusts over 25 mph across much of the forecast areas (90-99%), with gusts over 30 mph more likely along the coast (70-90%) than inland (40-60%). Gusts of 35 mph or greater remain a low for inland locations (5-20%) but are more probable along the coast (35-55%). While not currently forecasting wind advisory level, these speeds could still create issues for canopies, tents, and other unsecured gear.

Wind Advisory conditions for inland locations are as follows: Sustained Winds of 30-39 mph for durations of 1 hour or longer. OR Frequent Gusts of 45-57 mph for any duration.

We do not issue Wind Advisories for the coast.

By Tuesday, the low continues southeast with showers lingering along with a southerly flow pattern. This southerly flow pattern,is much more favorable for thunderstorm development and as such, there is a 15-20% chance for thunderstorms across the Willamette Valley and the Cascades starting late Tuesday morning/early Tuesday afternoon. For the middle of the week, the forecast trends towards warmer and drier weather as weak high pressure/zonal flow develops, though temperatures remain on the cool side compared to the weekend warm spell. /42~12

On a slightly personal note, with Monday being Memorial Day, it is time to remember those who served that are no longer with us. I want to remind everyone that if you are a fellow veteran or know a veteran that needs help, you can always call the VA Crisis Line by dialing 988 and pressing 1 or text 838255 24/7/365. We must take care of and look out those who stood besides us, who came before us and who will follow in our footsteps. Semper Fi. /42

AVIATION

At 2030z Sat, conditions have improved to VFR everywhere except for KAST. There's a 25-35% chance that the marine stratus never dissipates for the entire TAF period at KAST, but if it does, it should by 21-23z Sat. Light north to northwest winds less than 8 kts across inland areas will increase to 8-12 kts through the late afternoon and evening hours for locations north of KAST. Along the coast, winds are already increasing. Expect sustained winds around 8-12 kt with gusts up to 20-25 kts. Expecting winds to decrease around 04-08z Sun. As winds decrease, they are expected to shift slightly northeast south of KAST, which guidance indicates will limit the redevelopment of marine stratus. The exception is around and north of KAST where winds will remain more northwesterly, and if stratus does dissipate this afternoon, then redevelopment is likely by 09-12z Sun. Winds remain light and northerly on Sunday, shift back northwesterly along the coast.

KPDX AND APPROACHES...VFR conditions expected through the 00z TAF period. Northwesterly winds less than 8 kts increase to 8-12 kts with gusts up to 18 kts around 23z Sat - 01z Sun, decreasing by 06z Sun. Winds remain light and northerly Sunday. -03

MARINE

North winds continue across the waters this afternoon into Sunday, breezy with gusts up to 25 kts this afternoon and evening for locations south of Cape Falcon. A Small Craft Advisory remains in effect through 5 AM Sunday for these locations. Seas will be around 5 to 8 feet through Sunday night.

A frontal system will impact the waters Monday into Tuesday. Winds turn westerly and increase early Monday morning as the front approaches and moves through the waters. Latest guidance indicates widespread wind gusts up to 25-30 kts, strongest north of Cape Foulweather, with a 35-50% chance of gale force wind gusts, mainly isolated and right along the frontal passage from 1 AM to 11 AM Monday. Because of this, do not have confidence at this time to issue a Gale Watch. Waves are forecast to rise behind the frontal passage Monday afternoon into Tuesday morning. There's high confidence (90+% chance) of significant wave heights exceeding 13 feet. Additionally there's around a 25% chance significant wave heights could reach 18-19 feet for locations 20 nm and beyond west of the coast, and there's around a 10% chance they could rise to 20 feet for locations 30 nm and beyond west of the coast. Waves forecast to decrease through Tuesday afternoon to around 10-12 feet. -03