Saint Helens, OR Weather

Synopsis

Dry weather is expected through Saturday with overnight and early morning frost/freeze conditions across much of the region. Rain chances increase early Sunday morning as a broad upper level low moves over the region. An semi-active pattern continues through the middle of next week, with a brief period of dry conditions expected Tuesday with another round of light precipitation expected Wednesday. Beyond Wednesday, uncertainty increases as models ensembles diverge significantly from each other.

Discussion

Today through Friday...Transient upper-level ridging continues through this evening bringing clearing skies and light, offshore flow to the region. However, by tonight a broad upper level trough from the Gulf of Alaska will bring precipitation back into the forecast through at least early Monday morning. Current, high resolution ensemble guidance has rain beginning at the coast early Sunday morning and reaching inland locations through the afternoon, with the bulk of the precipitation expected to cease by Monday morning across the region. At this point, the chances for 0.25 inches of rain or more from 5 AM Sunday through 5 AM Tuesday are 80-90% along the coast and Coast Range, 70-80% along the I-5 corridor, and 60-70% in the Cascades and foothills. Even with the influx of precipitation into the region, seasonable conditions with milder overnight temperatures are expected to persist through at least the middle of next week. As the middle of next week approaches, forecast confidence decreases as the early week low pushes eastward, although long-range guidance does continue to support additional chances for rain, with 30-40% of ensemble members bringing another weather system to the Northeast Pacific Wednesday/Thursday, this system is not expected to be as impactful as the Sunday/Monday one. Overall, seasonable temperatures are favored to continue into the final week of October. As for those wondering what is expected for the final Saturday in October, ensemble guidance is pointing towards a drier solution with overnight lows above freezing. /42-36

Aviation

Through 12Z Sunday...Current ground observations as of 11Z Saturday show generally VFR conditions across the airspace. However, satellite observations are showing IFR conditions pushing up the Columbia River. These IFR conditions are expected to impact KPDX within the next few hours and are expected to persist through around 15Z-18Z Saturday. Along the coast, IFR/LIFR conditions are being observed north of KTMK and are also expected to persist through around 15Z-18Z Saturday. There remains a 5-10% probability of MVFR/IFR conditions to develop within the Willamette Valley through 15Z Saturday. Any lowered flight conditions should improve to VFR after 18Z Saturday and are expected to persist through the remainder of the TAF period. Also, expect winds to remain light and variable at all terminals through the TAF period.

Around 06Z Sunday, an incoming system will start to bring light precipitation and a mixture of high-end VFR/low-end MVFR to KAST. These conditions are expected to slowly spread south and east through what remains of the 12Z TAF period, with most terminals likely being impacted after 12Z Sunday.

KPDX AND APPROACHES...The current VFR conditions are expected to degrade to IFR within the next hour or two. These conditions are expected to persist through around 15Z-18Z Saturday with improvement towards VFR afterwards, through the remainder of the TAF period. /42

Marine

A slow-moving low will approach the outer waters late tonight into Sunday, bringing a transition to southerly winds. This system will also result in building seas towards 8 to 10 ft with southerly wind gusts approaching 25 kt. These conditions are expected to start in zone PZZ271 before spreading south and eastward through tonight. As a result, have issued a series of Small Craft Advisories across all waters through at least late Sunday night. By the start of next week, conditions look to subside below Small Craft Advisory thresholds. However, another system is expected to impact the waters by mid- week and result in around a 20%-30% chance for Small Craft conditions to return. /42