West Linn, OR Weather

Synopsis

A wetter and more active pattern is expected as a broad low moves into the region for the start of the week. A brief reprieve is expected on Tuesday, but by the middle of the week an active pattern is expected to return as multiple systems bring repeated rain chances with continued near-normal temperatures.

Discussion

Today through Saturday...A broad area of low pressure will slowly push eastward across the Pac NW for the start of the week. Rain and cooler temperatures are expected as a cold frontal boundary will spread southward along the coast early this morning, then push inland into the Willamette Valley by late this morning. Behind the initial rain band, scattered to numerous post-frontal showers this evening will linger into early Tuesday morning before trending drier. The break from rain showers may be brief as another shortwave tracks overhead late Tuesday, followed by yet another upper low from Wednesday through the remainder of the workweek. While rain is unlikely to persist through this entire period, these systems will bring repeated chances for rain at the end of what has been an unusually dry October in the Pacific Northwest. Ensemble mean 48-hour rainfall totals from 5 AM today through 5 AM Tuesday are 0.50-1.10 inches, with the reasonable high-end amounts of 1.50-2.25 inches also likely insufficient to support any flooding concerns.

Temperatures through the period will remain near seasonal norms, namely afternoon highs in the low 50s to low 60s and overnight lows in the mid 30s to mid 40s. Increased cloud cover will help limit the threat of freeze or frost conditions until late next week when there is a chance of clearer overnight skies allowing for colder temperatures.

Now, what people might want to know about is: Will this system bring any chance of snow to the Cascades? Well, snow levels are expected to fall towards 5000 ft as 850mb temperatures look to drop towards 1C to -1C through the start of this week. This will allow for light accumulations in the Cascades above pass level through Wednesday, with accumulations to lower elevations possible later in the week as 850 mb temperatures look to reach 0C to -2C by Friday. So, don't be surprised if to look towards the peaks of Mount Hood, Mount Saint Helens and The Three Sisters and see some snow. With that in mind, now is the perfect time to check on any winter weather equipment and emergency supplies for your household and vehicles. /42-36

Aviation

Through 12Z Monday...Generally VFR conditions with high clouds throughout the airspace. However, these conditions are expected to only last through around 13Z-15Z Sunday as radar and ground observations show a cold front slowly pushing inland this morning. This frontal system has already brought MVFR conditions along with rain to KAST and these conditions are expected to slowly develop for all other TAF locations. KONP should see these conditions by 11Z-13Z Sun, with inland terminals seeing them by 14Z-16Z Sun (from north to south). Through the TAF period, probabilistic guidance is suggesting a mixture of high-end VFR/low-end MVFR with a 10-20% chance of IFR conditions at any given time through the TAF period across the airspace.

Expect southerly winds to develop before the frontal passage and persist through the TAF period. Gusts up to 25 kt are expected along the coast with gusts up to 20 kt for inland locations through 00Z Monday. Could see some LLWS near KPDX from 17Z-19Z Sunday as the frontal passage is expected around that time.

Chances of MVFR conditions decrease toward the end of the TAF period for inland locations with predominately VFR conditions expected after 03Z Monday. Coastal locations will likely maintain predominately MVFR conditions after 03Z Monday and through the remainder of the TAF period.

KPDX AND APPROACHES...Expect VFR conditions with high clouds until around 15Z Sunday as a frontal system is expected to start to impact the terminal around that time. As the frontal system arrives, expect rain and a 30-60% chance of intermittent MVFR conditions and 10-15% chance of IFR conditions at any given hour from 15Z Sunday through 03Z Monday. South/southeast winds will persist through the TAF period around 5-10 kt. Chances of MVFR conditions decrease toward the end of the TAF period with predominately VFR conditions expected after 03Z Monday.

Could see some LLWS near KPDX from 17Z-19Z Sunday as the frontal passage is expected around that time. /42

Marine

A slow-moving and steadily weakening area of low pressure will traverse waters through today. Expect southerly winds across all waters with gusts approaching 30 kt and seas building towards 9-12 ft. Current buoy observations at 46089 as of 0100 AM show seas around 10 ft with southerly gusts around 20-25 kt. Am expecting similar conditions to slowly spread across all waters, to include the Columbia River Bar through early this morning. Therefore am maintaining the current suite of Small Craft Advisories, with staggered onset times as hazardous conditions spread from northwest to southeast.

Small Craft conditions are expected to persist across all waters through at least very early Monday morning, with winds and seas most likely starting to subside by Monday morning for our northern water zones. These sub Small Craft conditions are expected to spread from the northwest to southeast as well. Current guidance is showing a brief period of relatively calmer conditions through Tuesday. However, there is a 30% chance that another system approaching the waters mid-week that could yield in another round of Small Craft Advisory conditions. /42-36