textproduct: Portland

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 18z Monday

A cold frontal rain band is bisecting the airspace as of 17z Sun, extending from K6S2/Florence to the NNE across Portland-area terminals and into the south WA Cascades. This feature will progress eastward, passing east of the Willamette Valley by 00z Mon, and east of the Cascade crest by 06z Mon. While the front is overhead, MVFR cigs/vis are favored at area terminals, with persistent 15-25% chances for brief IFR cigs/vis if heavier rain elements pass overhead. Behind the boundary, a slight improvement of flying conditions is expected, as currently observed as KAST, although restricted vis/cigs may linger a few hours after precipitation eases. Post-frontal rain showers are also likely to persist through the remainder of the period, yielding brief periods of MVFR conditions if they pass over a terminal. More widespread MVFR cigs are again favored after 12z Mon within the nocturnal boundary layer.

South to southeast winds around 5-10 kt expected at inland terminals, veering out of the south behind the boundary along the Willamette Valley. Low pressure offshore will maintain enough of a pressure gradient to see gusty east winds continue near the western Columbia Gorge at KTTD. At the coast, south winds of 10-15 kt gusting to 20-25 kt will continue into this evening.

KPDX AND APPROACHES...MVFR cigs/vis with steady light rain favored as the frontal boundary progresses eastward through 00z Mon, with persistent 15-25% chances for period of IFR cigs/vis if heavier rain elements pass over the terminal. Post-frontal rain showers should accompany a slight improvement to low-end VFR after 00z Mon, with increasing chances for further MVFR cigs after 12z Mon. Southeast winds 5-10 kt persist through the period. -36

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. The current Small Craft Advisories are therefore maintained, 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

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory until 5 AM PDT Monday for PZZ210-251-271.

Small Craft Advisory until 11 AM PDT Monday for PZZ252-272.

Small Craft Advisory until 5 PM PDT Monday for PZZ253-273.