textproduct: Portland

SYNOPSIS

Shower activity continues to decrease today, but cannot rule out some isolated, lingering showers through the afternoon. A shortwave ridge builds over the area through Tuesday afternoon. Then, the first in a series of systems arrives by Tuesday, bringing widespread rain. Wet and cool weather continues through the middle of the week and into weekend. There is the potential for much colder temperatures for the latter part of this week and through the weekend.

LONG TERM...Thursday through Sunday

Wet weather is expected to continue through the latter part of the week and into the weekend as a system move into the region. While the current deterministic track of this system has it taking aim at Vancouver Island, before stalling briefly, then diving southward on Saturday. There is a lot of uncertainty with the exact track and magnitude of the system, which means that precipitation totals as well as temperatures for the holiday are resulting in a challenging forecast. However, 48 hour liquid precipitation exceeding 0.50" from 4 AM Thu to 4 AM Sat are around 40-60% along the the coast, Coast Range, Willapa Hills, and Cascades and 20-50% across interior, lowland valleys.

Given the high uncertainty with the aforementioned system, the majority (50-70%) of ensembles are showing cooler air coming into the region Saturday into Sunday. The 00Z run of the GFS has 850 mb temperatures of -2 to -7 C, while the same run of the ECWMF has 850 mb temperatures of 1 to 5 C. So, with this vast of a temperature spread, you may notice towards the end of the forecast period (Saturday night into Sunday) that there is a mention of a rain/snow mix all the way down to the Willamette Valley floor and southwest WA lowlands. While a rain/snow mix is possible, the probabilities for this outcome to occur are currently very low (1-5%). To summarize, overall model spread is very large for both temperatures and precipitation amounts. This means forecast confidence is very low. However, we will remain vigilant over the next few days and will update the forecast as needed. /42

AVIATION

What remains of a weak frontal passage will continue to push eastward out of the local air space. This is resulting in northwesterly flow aloft and with flight conditions generally improving towards predominately VFR with isolated pockets of MVFR. Another weak front may bring some very light showers to northern portions of the area through around 00Z Tuesday, with little to no impact to overall flight conditions expected. A shortwave ridge will build over the region after 00Z Tuesday and will bring about a 15-30% chance for IFR/LIFR conditions developing along the I-5 corridor starting around 06Z Tuesday and persist through at least the remainder of the TAF period.

KPDX AND APPROACHES...Predominately VFR conditions expected through the majority of the TAF period. A weak front may bring some very light showers to northern portions of the area through around 00Z Tuesday. Around 06Z Tuesday, there is a 15-30% chance for IFR/LIFR conditions developing at or near the terminal through at least the end of the TAF period. /42

MARINE

Seas will remain around 9 to 12 ft before falling to 7 to 9 ft by Monday afternoon and then 6 to 8 ft on Tuesday. The next frontal passage arrives Tuesday night into Wednesday, bringing wind gusts up to 30 kt with a 15-30% chance for gale force wind gusts up to 35 kt. Confidence remains low, so will refrain from issuing a Gale Watch at this time. Even if gale force wind gusts to 35 kt do occur, it appears the coverage and duration for wind gusts of this magnitude will be limited. Seas build towards 10 to 13 ft with this frontal passage with seas expected to peak on Thursday. There is some uncertainty as to the exact path of this system. As such, there is currently a 10% chance seas will peak around 16-19 ft, with a 1-5% chance for seas will reach 20 ft or higher Thursday into Friday. /42

BEACH HAZARDS

An energetic westerly swell is expected along the northwestern Oregon and southwestern Washington coasts through Monday. A westerly swell with wave heights around 10-14 ft and a predominant wave period between 14-16 seconds will result in a high sneaker wave threat. These energetic waves can run significantly farther up a beach than normal, including over rocks and jetties, creating potentially life-threatening conditions in the surf zone when beachgoers can be unexpectedly knocked off their feet and pulled out into cold ocean waters.

A Beach Hazards Statement remains in effect through 10 AM Monday to cover the high sneaker wave threat. Caution should be used when in or near the water, and beachgoers with children should be especially watchful. Never turn your back on the ocean, and be sure to keep an eye on the waves. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 10 AM PST this morning for PZZ210- 251>253-271>273.