textproduct: Portland

SYNOPSIS

A wetter and more active pattern returns from Sunday through much of the next week as multiple systems bring repeated rain chances with continued near-normal temperatures.

DISCUSSION...Now through Saturday

Dry weather today will give way to wetter conditions Sunday as a closed upper low and its associated surface low slowly track onshore and fill over the north Oregon coast through the first half of the workweek. There is strong consensus that rain along the cold frontal boundary will spread southward along the coast overnight, then push inland to the Willamette Valley through Sunday morning. Behind the initial rain band, scattered to numerous post-frontal showers Sunday evening will linger into early Tuesday 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 Sunday through 5 AM Tuesday are 0.75-1.50 inches, with the reasonable high-end amounts of 1.5-2.5 inches also likely insufficient to support any flooding concerns. Snow levels falling to around 5000 ft will allow for light accumulations in the Cascades above pass level through Wednesday, with accumulations to lower elevations possible later in the week.

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. -36

AVIATION...Through 06Z Monday

Currently VFR conditions and high clouds throughout the airspace. While VFR conditions and high clouds will likely persist through the TAF period, coastal terminals will begin to see deteriorated MVFR conditions around 08-12Z Sun as a frontal system arrives. Specifically, expect rain to arrive at KAST by 07-09Z Sun and KONP by 11-13Z Sun, and at inland terminals by 13-18Z Sun (from north to south). During this system, probabilistic guidance suggests a 30-60% chance of MVFR conditions and a 10-20% chance of IFR conditions at most terminals. Otherwise, expect light and variable winds tonight to become south to southeasterly and increase to around 5-10 kt inland by 12-18Z Sun and 10-15 kt with gusts up around 20-25 kt along the coast by 09-12Z Sun. Chances of MVFR conditions decrease toward the end of the TAF period but deterministic guidance still shows the possibility of MVFR conditions lingering beyond 03Z Mon at a few terminals. Based off how the models are trending, there is improving confidence that conditions will improve back to VFR by 03Z Mon, but not enough confidence to include at every terminal in the TAFs.

KPDX AND APPROACHES...Expect VFR conditions high clouds, and light and variable winds until around 15Z Sun as a frontal system arrives. As the frontal system arrives, expect rain and a 30-60% chance of MVFR and 10-20% chance of IFR conditions. Southeasterly winds around 5-10 kt develop around 12Z Sun ahead of the incoming front. Chances of MVFR conditions decrease toward the end of the TAF period but deterministic guidance still shows the possibility of MVFR conditions lingering beyond 06Z Mon. ~12

MARINE

A slow-moving and steadily weakening area of low pressure will traverse waters late tonight into Sunday, causing winds to back out of the south with gusts approaching 25 kt and seas building towards 8-10 ft. Small Craft Advisories therefore remain in effect, with staggered onset times through this evening and tonight as hazardous conditions spread from northwest to southeast. While winds and seas are most likely to subside by Monday afternoon, there is a 30% chance that another system approaching the waters midweek will yield conditions hazardous to small craft. -36/42

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT Sunday for PZZ210.

Small Craft Advisory until 11 AM PDT Monday for PZZ251.

Small Craft Advisory from 2 AM Sunday to 11 AM PDT Monday for PZZ252-272.

Small Craft Advisory from 8 AM Sunday to 11 AM PDT Monday for PZZ253-273.

Small Craft Advisory until 11 AM PDT Monday for PZZ271.