Tualatin, OR Weather

Synopsis

Largely dry weather expected through midweek. Above average temperatures today and Wednesday. Chances for wetter and cooler weather return late in the week with potential for a more robust system over the weekend.

Discussion

Now through Monday...Dry conditions are expected through at least Thursday. The upper level low continues to pinch off from the main flow as it drops south toward California today. In its wake, shortwave ridging will build into the PacNW today. Cloud cover will dissipate through the day with light offshore winds developing on the eastern flanks of the Cascades and coast range and through the western Columbia River Gorge. These offshore winds are not expected to be impactful though they may be locally gusty up to 40 mph in the typical spots within the Gorge. Highs jump to around10 degrees above normal today and Wednesday, translating to afternoon highs in the 60s on the coast and in terrain, and in the low to mid 70s within inland valleys.

The latter half of the week again trends toward cooler temperatures and modest chances for rain. Cluster analysis shows good agreement in troughing developing over the Gulf of Alaska and dropping southeast toward the PacNW Thursday into Friday. This pattern would favor a return to near normal temperatures and chances for light precipitation. Currently, the best chances for precipitation are over the Cascade Foothills and areas east of I-5 but remain rather low at 20-40%. Rainfall associated with this system is not expected to be noteworthy if it occurs at all. Overnight lows Thursday and Friday night are expected to be much cooler than the start of the week. More widespread temperatures below 37 degrees are possible throughout the central and southern Willamette Valley, Cascade Foothill valleys, and parts of the coast range valleys. If trends continues, will likely need Frost Advisories for some or all of these locations.

Details heading into the weekend remain murky as ensembles solutions remain undecided in regards to the developing pattern. There is a low to moderate chance that a robust shortwave develops over the Gulf of Alaska and drops southward, supporting a surface low as it approaches the PacNW. Around 30-40% of ECMWF ensemble members depict both of these features heading into Saturday and Sunday. However, there is a noticeable trend in several of the members to keep the core of the surface low offshore and even has it retrograding back out to sea during the latter half of the weekend. This current trend signal lower potential for much needed rainfall across the area but also lower chances for impactful winds across the region. Given this potential system is still several days out, details remain unclear and will hopefully be fleshed out in the coming days. -19

Aviation

Through 12Z Wednesday...High level clouds continue to stream in from the south as an upper level low drifts south. This cloud cover is expected to inhibit most, if not all, fog development. Offshore flow is expected to increase after 15-18Z today, bringing increasing easterly winds to KTTD and Portland metro terminals and increasing northeast winds to KUAO. Winds will increase out of the north from KSLE to KEUG. Strongest winds will be at KTTD and east into the Gorge with gusts up to 25 kts at KTTD and up to 30-35 kts through the western Gorge. Winds along the coast turn northeasterly around 5 kt with KONP winds turning more northerly during the afternoon.

KPDX AND APPROACHES...VFR flights conditions will continue through the TAF period with high clouds dissipating through the day. Northwest winds around 5 kt increasing and turning easterly after 18z as an offshore pressure gradient strengthens. Expecting sustained winds around 8-11 kt with occasional gusts around 20kt. Winds begin decreasing after 00-02z Wed. -19/03

Marine

Northerly winds continue across the waters in the wake of a system that is dropping southward. Widespread wind gusts up to 25 kt will be possible over the outer waters beyond 10 nm offshore through the afternoon. A Small Craft Advisory remains in effect for the outer waters through 5 PM. Beyond 5 PM tomorrow, winds and seas will be on the decrease as high pressure returns.

Winds and seas are set to increase again Thursday into Friday morning with the passage of a weak cold front, especially over the northern waters to the north of Cape Falcon where conditions will likely be hazardous to small craft. There is the potential for a stronger low pressure system over the upcoming weekend, bringing a 20-40% 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 is low at this time, and the forecast is worth monitoring over the next several days. -19/23