textproduct: Portland

SYNOPSIS

An active and progressive weather pattern continues this weekend into next week as the next quick hitting weather system moves through the region overnight into Saturday. Breezier southerly winds return Saturday evening into early Sunday as well. From there we switch to more of a NW-WNW flow pattern next week with lowering snow levels and growing potential for impactful snowfall across the Cascades, including the passes, mid-week.

LONG TERM...Monday through Thursday

Overall, ensemble guidance is pointing towards a fairly typical cooler winter- time weather pattern for the Pacific Northwest with snow levels remaining at or below pass-level by the middle of the week. This is certainly a positive development for those who enjoy snow related recreation. As Monday progresses weak ridging moves overhead in between weather systems leaded to a lull by Monday night into Tuesday morning although clearer skies, ample surface moisture, and lighter winds will be a recipe for widespread fog and visibility should the timing of the ridge pan out. Then the second half of Tuesday to Wednesday, guidance suggests another system will move in from the northwest, bringing another round of lowland rain and Cascade snow. This time, it looks like the Cascades may get warning- level snow (12in+). Chances for 1 foot of snow or more in a 48 hour period from 4 AM Tuesday to 4 AM Thursday are around 50-70% for all our Cascade passes including Hwy 26 at Government Camp, Santiam Pass, and Willamette Pass. The current forecast has roughly 10-20 inches of snowfall across the Cascades through this same period. Should this hold, a winter storm watch/warning may be needed - likely our first issuance this product type for the Cascades so far this winter. By the end of the week, almost all ensemble modeling systems show a ridge of high pressure moving over the Pacific northwest, however, there is a 24-36hr difference between ensemble clusters resolving exactly when the axis of this feature moves overhead. Around 55% have the ridge moving overhead on Friday while the other 45% of ensemble members hold it off until the weekend. In either case a temporary dry break is on the horizon. -99/10

AVIATION

A low pressure system off the northern California coast will maintain moist southerly flow and periods of rain showers across the area through Saturday. A bit of a lull in shower activity expected through this afternoon. VFR conditions have generally returned to the coast, while IFR to LIFR CIGs are likely to persist inland through this afternoon. Conditions should improve this evening, trending toward a mix of MVFR and lower end VFR after 00z Friday.

After 06z Sat, another frontal band moves through the area from the south, returning showers and lower CIGs. By 08-10z Sat, there is a 40-50% chance for MVFR conditions, with the highest chances across the Willamette Valley. Offshore flow continues along the coast and eastern Portland Metro terminals, with gusts to 25 kt at KTTD. Elsewhere, winds remain light and variable, turning more southerly early Saturday morning with the next front.

KPDX AND APPROACHES...IFR CIGs continue to persist this afternoon. By 03z, chances increase for conditions improving to MVFR or lower-end VFR. Rain showers increase again after 08z with conditions gradually trending back toward MVFR. ESE winds around 5-10 kt expected through the period. /DH

MARINE

Offshore east to southeast winds expected through this evening across the coastal waters as a broad area of low pressure spins off the southern Oregon and northern California coasts. There is still uncertainty between the models whether a double barreled low continues or a single compact surface low develops over the next 24-36 hours. This area of low pressure is expected to gradually move northeastward on Saturday, eventually lifting toward Vancouver Island by Saturday night. At this time, expect winds to become more southerly by early Saturday and increase through the day. The strongest winds are likely across the outer coastal waters, so have issued a Gale Warning for those zones south of Cape Falcon for wind gusts up to 40 kt, likely peaking Saturday afternoon and early evening.

Seas will also build tonight into Saturday, becoming very steep and hazardous. Seas will initially be driven by increasing wind waves, followed by a fresh southerly swell moving through the waters. Highest seas are expected Saturday evening, likely peaking at around 16 to 18 ft with a period of 11-12 seconds.

Because of the uncertainty that remains in the track of the low Saturday night, have maintained a Gale Watch across much of the coastal waters into early Sunday morning. There remains around a 30% chance for Gale force wind gusts across the northern waters, as well as within the inner coastal waters during this timeframe. Winds turn more onshore late Saturday night into Sunday as the low lifts north, with southwest winds gradually decreasing across the area through Sunday night as a weak front pushes inland. High pressure briefly returns early next week, while seas are expected to fall below 10 ft late Sunday night into Monday. More active weather returns by Tuesday as a potential gale force front moves across the waters. /DH

BEACH HAZARDS

Perigean Spring (King) tides are back this first week of January, which will result in the highest tides of the season. A Coastal Flood Advisory for minor tidal overflow has been issued from 10 AM to 2 PM Saturday along the Clatsop and Tillamook Coast, and South Washington Coast. Minor flooding up to one foot above ground level during high tides is expected in the low lying areas near bays, sloughs, and the lower reaches of the coastal rivers. The tidal gauges at Toke Point and Astoria have forecast tides of up to 11.8 feet, while the tidal gauge at Garibaldi has a forecast tide up to 10.8 feet. Minor tidal overflow is expected to continue through the weekend during high tide.

PQR WATCHES/WARNINGS/ADVISORIES

OR...Coastal Flood Advisory from 10 AM to 2 PM PST Saturday for ORZ101-102.

WA...Coastal Flood Advisory from 10 AM to 2 PM PST Saturday for WAZ201.

PZ...Small Craft Advisory until 6 PM PST this evening for PZZ210.

Small Craft Advisory from 1 AM to 7 PM PST Saturday for PZZ210- 251>253.

Gale Watch from Saturday evening through Sunday morning for PZZ251>253-271.

Small Craft Advisory until 7 PM PST Saturday for PZZ271.

Small Craft Advisory until 10 AM PST Saturday for PZZ272-273.

Gale Warning from 10 AM to 10 PM PST Saturday for PZZ272-273.