textproduct: Portland

SYNOPSIS

A fairly progressive upper-level weather pattern and a series of frontal systems with bring cooler than average temperatures and periodic rounds of showers to the area through Wednesday, June 10. There is also a 15-30% chance of short-lived thunderstorms Saturday afternoon and a 10-20% chance Tuesday afternoon. Upper level ridging will bring a warming and drying trend June 11-15, with potential heat concerns June 12-15.

LONG TERM...Tuesday through Thursday night

The long term forecast starts out with cooler than average temperatures and occasional showers, and ends with a warming and drying trend. Despite the model timing differences discussed above with the arrival of a frontal system late Sunday into Monday, ensemble guidance is in good agreement the area will be solidly within a post-frontal showery environment Tuesday through Wednesday under a broad upper level trough. This will maintain cooler than average temperatures and occasional rain, with high temperatures most likely in the 60s. It appears showers will be most frequent on Tuesday, which is also when the NBM suggests there is a 10-20% chance of thunderstorms during the afternoon. NBM 48-hr probabilities for rain amounts over 0.25" peaks between 5 AM Monday and 5 AM Wednesday, showing anywhere from a 45-75% chance for most locations in southwest WA and northwest OR, except an 80-90% chance in the Cascades.

Conditions begin trending warmer and drier from Thursday onward. Cluster analysis for June 11-15 for 500 mb heights generally suggest upper level ridging will gradually develop over the region. This will bring a prolonged stretch of dry weather, with temperatures likely warming each day. While confidence is high temperatures will warm significantly compared to early in the week, confidence is low regarding exactly how warm temperatures will get. The NBM 1D Viewer for high/low temperatures reflects this uncertainty well, showing large model spread June 11-15. For example, the NBM 10th-90th percentile for high temperatures June 13-15, which will likely be the warmest days, ranges from the upper 70s to near 100 degrees for inland valley and upper 60s to upper 80s for coastal locations. Probabilities for a moderate HeatRisk or higher reach 25-45% for inland valleys on June 12, 50-75% on June 13, and 65-85% on June 14. There is a 5-20% chance for a major HeatRisk or higher on June 13 and a 10-30% chance on June 14. Regardless of what materializes, those planning on swimming in rivers or lakes should exercise cold water safety and be mindful of the dangers that come with cold water. Those who are sensitive to heat and/or have outdoor plans should keep an eye on the forecast over the next week. -23

AVIATION

Predominately VFR conditions expected over NW Oregon and SW Washington through Saturday afternoon. At 23z Fri, isolated showers continue over the region, mainly limited to the coast and terrain north of KONP. Shower activity will increase after 08-12z Sat along the coast then spreading inland 10-12z Sat as a weather system moves east into the region. Some showers could be heavier, causing brief periods of MVFR cigs or vis. Additionally, there's a 20-30% chance of thunderstorms near and north of KSLE and KTMK and 10-20% chance elsewhere west of the Cascades between 16z Sat to 00z Sun. Best chances will be 18-22z Sat with shower and thunderstorm chances diminishing quickly after. Any stronger shower could produce heavy rain that could cause brief periods of MVFR/IFR conditions, small hail, gusty and erratic winds, and lightning.

Current winds are westerly across the region around 8-10 kts at most TAF sites. Winds will decrease around 04-06z Sat, becoming southerly inland and less than 6 kts. Winds increase to 8-11 kts after 14-16z Sat as the weather system approaches, shifting westerly again after 18-20z.

KPDX AND APPROACHES...VFR conditions through the TAF period. A few stray light showers possible before 10z Sat, then shower activity becomes more likely after 10-12z Sat with a 30% chance of thunderstorms 18-22z Sat. Any stronger shower or thunderstorm could produce heavy rain that could cause brief periods of MVFR conditions, small hail, gusty and erratic winds, and lightning. Westerly winds 10-12 kts shift southerly and decrease below 6 kts after 04-06z Sat, increasing and shifting westerly again after 18-20z Sat. -03

MARINE

Overall fairly benign conditions expected through the weekend and into next week. Expect a series of weak frontal systems which will bring increasing winds and building seas. The first of these frontal systems arriving today allow seas to build into the 5-8 ft range at 10-12 seconds with westerly winds gusting up to 20 kt. Then a more robust front arrives Saturday, bringing more northwesterly winds by the afternoon. Winds only increase marginally with only a 10-25% chance for Small Craft Advisory wind gusts - highest probabilities across the outer waters. Given the minimal confidence in Small Craft conditions, have decided to not issue any headlines at this time. After a lull during the day on Sunday as high pressure briefly returns, winds increase yet again on Monday as a comparatively stronger system moves over the waters, bringing south wind gusts up to 25 kt and seas approaching 5-8 ft. Conditions then gradually calm into the middle the of the week as a ridge of high pressure attempts to rebuild overhead and northwesterly winds return while seas hold around 5-7ft around 9-11 seconds. /42-99

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.