Aloha, OR Weather

Synopsis

Mainly dry conditions will continue through early Saturday. Low-level offshore flow and abundant sunshine will result in afternoon high temperatures that are around ten degrees above normal for inland valleys. Winds turn onshore later this afternoon. Trending cooler Thursday through Tuesday with widespread morning frost Friday and Saturday. Chances for rain are mainly focused on the Saturday evening through Sunday morning time frame when chances increase to 30-50%.

Discussion

Now through Tuesday...Dry conditions for most of the forecast area through early Saturday. Shortwave ridging remains in place today, supporting another day of well above average temperatures with interior lowlands peaking in the low to mid 70s and 60s along the coast. Offshore winds continue through the morning on the eastern slopes of the Cascades and through the Columbia River Gorge. Wind gusts in the western Columbia River Gorge could still reach 20-30 mph through around 11 am today. Winds will eventually turn onshore as a trough approaches from the northwest.

Cooler temperatures are expected through the rest of the forecast period as several troughs move over the region. Temperatures in the 60s are expected over the lowlands and 50s at the coast from Thursday onward. Ensembles continue to trend drier with the system passing through on Thursday with most of the forecast area expected to remain dry. The best chances for precipitation will be over the Cascades and Cascade Foothills, mainly in eastern Lane and Linn counties where PoPs peak between 20-40%. The main concern during this time period will be widespread morning frost Friday and Saturday, bringing impacts to those with agricultural interests. Saturday morning is shaping up to be the coldest morning, as this is when some locations could fall below- freezing; the NBM is showing a 25-50% chance for lows of 32 degrees or colder in the southern Willamette Valley, except higher chances greater than 80% from Creswell to Cottage Grove and near 15% in Eugene.

Details heading into the weekend remain murky as ensembles solutions continue to vary. There is a moderate chance (30-40%) that a robust shortwave develops over the Gulf of Alaska and drops southward, supporting a surface low as it approaches the PacNW. Ensemble members continue to trend drier with more solutions favoring the surface low remaining offshore or tracking farther north into Canada. This current trend signal lower potential for much needed rainfall across the area but also lower chances for impactful winds across the region. That being said, PoPs have decreased to 30-50% late Saturday through Sunday. Chances for 0.25 inches of rain remain around 20-40% for most locations, slightly higher near 40-50% along the coast. Lastly, chances for impactful winds have also decreased with the potential system this weekend, with less than a 5% chance for wind gusts of 40-45 mph or stronger. Therefore, impacts are unlikely to occur this weekend and there's a notable chance conditions will remain dry. Chances for rain decrease even more on Monday and Tuesday to 10-15%. -19/23

Aviation

Through 18Z Thursday...High pressure over the region will lead to predominantly light winds and VFR conditions through 18z Thursday. The main exception to this will be between 09-18z Thursday when clear skies, light winds and low level moisture will lead to pockets of fog and low clouds developing at several taf sites. The highest probabilities for IFR conditions developing are at KEUG and KHIO between 09-18z Thursday where there is a 30-40% chance for these conditions occurring at any given hour during that timeframe. There is around a 20% chance of IFR conditions developing at any given hour at our remaining taf sites during this time period. In addition, there is a signal that marine clouds along the coast may result in a period of IFR conditions along the central coast of Oregon this evening, primarily between 00-05z Thursday.

KPDX AND APPROACHES...High pressure over the region will lead to light winds and predominantly VFR conditions through 18z Thursday. The main exception to this will be in the 12-18z Thursday time period when there is a 20-30% chance for MVFR to IFR conditions developing at any given hour.

Marine

Northerly winds expected to remain below 20 through early tonight with seas 5-7 feet at 11-13 seconds. Winds and seas are set to increase again late tonight through Friday morning with the passage of a decaying front. Winds will be strongest over the northern waters north of Cape Falcon where wind gusts of 25-30 kt will be possible. Elsewhere, winds are expected to be slightly lower but still hazardous to small craft. Therefore, Small Craft Advisories have been issued for late tonight into Thursday evening. Later Thursday evening, a steep westerly swell may push wave heights to 10-12 feet at 9-11 seconds which would warrant a Hazardous Seas Advisory for the waters north of Cape Falcon. Decided to hold off on issuing Hazardous Seas headlines in case an extension of the Small Craft Advisories suffices.

There is the potential for a stronger low pressure system over the upcoming weekend, bringing a 10-30% chance for gale force wind gusts and seas over 10 feet. Overall confidence in the exact track and strength of this potential low pressure system remains low at this time. It is worth noting that chances have decreased for significant winds and seas with today's forecast update due to a less favorable low track. -19/23