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

A mixed bag of flight conditions is occurring this morning, with mainly VFR conditions at the coast and mainly IFR/MVFR conditions inland. There are also pockets of LIFR cigs occurring, mainly impacting KHIO. Expect conditions to trend towards MVFR to VFR this afternoon, before areas of fog and low clouds redevelop over the Willamette Valley this evening into tonight. Meanwhile, the coast should remain VFR due to the development of offshore flow. KTTD will likely remain VFR for the same reason. Fog/cigs will likely attempt lifting at least a bit towards 12-16z Tuesday as widespread rain begins pushing into the region from the west.

KPDX AND APPROACHES...Cigs will likely fluctuate between MVFR/VFR this morning through 21z Monday before trending towards mainly VFR thereafter. By 08z Tuesday, fog and low clouds will attempt developing at the terminal before lifting towards 12-13z Tuesday as rain begins to move in from the west. -23

MARINE

Seas have fallen to 7 to 9 ft as expected. Expect westerly winds to continue weakening through today, before becoming easterly for a brief period of time tonight. The next frontal passage arrives late Tuesday into Wednesday, bringing a shift to southerly winds with gusts up to at least 30 kt. There is a 15-30% chance for gale force wind gusts up to 35 kt, except around a 50% chance over the northern outer waters. 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. Therefore, have decided not to issue a Gale Watch or Warning for this frontal passage. Seas build to at least 10 to 13 ft with this frontal passage with seas expected to peak on Thursday. There is some uncertainty regarding how high seas will peak on Thursday. 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. -23/42

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.