textproduct: Portland

SYNOPSIS

Largely dry weather is expected through Thursday with nightly chances for fog and frost in interior valleys and gusty east winds through the Columbia River Gorge. There is moderate to high confidence in a return to cooler and wetter weather Thursday night through the weekend.

LONG TERM...Thursday Night through Monday

Late in the week, ensemble guidance remains confident that ridging will shift east of the Rockies and broad upper-level troughing will set up over the western CONUS. An initial frontal system will mark this pattern shift with rain returning as early as Thursday night to the coast and spreading inland through Friday. Chances for precipitation then linger through the weekend as the forecast area remains within the upper trough. There does remain some uncertainty in the details of the flow aloft, however, with a cluster of ensemble members favoring a scenario where the upper trough pinches off into a closed low over California. While this scenario would leave the Pacific Northwest drier through the weekend, those members still suggest increased chances for precipitation early next week.

Cooler temperatures within the upper trough will bring snow levels back down to 3000-4000 ft, allowing for accumulating snow at the Cascade passes. Given uncertainty in the pattern aloft though, confidence remains low in forecast snow amounts. There are 45-55% chances of six inches or more of snow from 4 AM Saturday through 4 AM Tuesday, and 10-25% chances of one foot or more snow over the same period. There is additionally a 10-25% chance that snow levels fall below 1000 ft during the overnight hours Saturday night into Sunday and Sunday night into Monday, which could bring light snow to the West Hills. While snow reaching down to the valley floor cannot be ruled out (less than a 10% chance), marginal temperatures would severely limit any accumulations and impacts are unlikely. -10/36

AVIATION

Areas of fog and low stratus early this morning have yielded IFR flying conditions at many area terminals which are likely to continue through at least an hour or two after sunrise, generally 16-18z Tue. The lowest confidence in persistent IFR vis is at terminals east of the Columbia Gorge in the Portland area and along the Willamette Valley where marginally higher winds and resultant surface mixing have improved surface vis as earlier fog lifts to IFR cigs and, in some cases, skies trend clearer.

After conditions improve through this morning, VFR conditions are favored through the remainder of the period beneath sct high clouds. Strengthening offshore flow will see east winds gusting up to 25 kt develop at KTTD, and north to northeast winds around 10 kt elsewhere. There is low confidence in the recurrence of fog tonight as colder temperatures may instead favor frost.

KPDX AND APPROACHES...IFR conditions with fog or low stratus are likely to continue through at least sunrise, then rapidly clear to VFR conditions beneath sct high clouds after 15-17z Tue. East to northeast winds around 10 kt this afternoon will ease to around 5 kt and shift out of the north tonight. -36

MARINE

Buoy observations early this morning depict seas continuing to ease below 10 ft; Small Craft Advisories in effect have therefore been allowed to expire. North winds have begun to develop in response to a thermal trough extending northward along the coast. As winds rise to 15-25 kt through today, conditions will again become hazardous to small craft, with further Small Craft Advisories in effect across the outer waters (beyond 10 NM) from Cape Falcon south to Florence from 10 AM PST today through 4 PM PST Wednesday, and from Cape Shoalwater south to Cape Falcon from 4 PM PST today through 10 AM PST Wednesday. At this time, winds and gusts across the inner waters (within 10 NM) look to remain at 15-20 kt or less, however any increase in forecast winds may result in Advisories being expanded eastward to the coast. As thermal troughing weakens on Wednesday, winds will ease below hazardous thresholds. Meanwhile, a west to west-northwest swell will continue to subside from 8-9 ft today to 6-7 ft on Thursday.

Long-range guidance continues to favor a return to more active and impactful weather late in the week and through the weekend. Multiple frontal systems may bring repeated chances of rain and elevated seas. While the threat for abnormally strong winds appears low (chances for gale force wind gusts only peak around 5-15% Friday through the weekend), confidence is high seas will be on the increase, peaking around 14-16 ft Friday morning with the arrival of a long period westerly swell. There is a 15-25% chance seas will instead peak above 16 ft. -36/23

BEACH HAZARDS

A high threat for sneaker waves is likely Friday through Sunday evening due to a long period westerly swell. Waves can run up significantly farther on a beach than normal, including over rocks and jetties. Sneaker waves can suddenly knock people off of their feet and quickly pull them into the frigid ocean which may lead to serious injury or drowning. Caution should be used when in or near the water, especially those who will be razor clamming. Keep children and pets away from the surf zone. Keep off of jetties, rocks and logs near the surf zone. If you see someone swept into the sea do not swim in after them. Call 911 and keep an eye on them until help arrives. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...Dense Fog Advisory until 9 AM PST this morning for ORZ108-109- 114>118.

WA...Dense Fog Advisory until 9 AM PST this morning for WAZ204-205.

PZ...Small Craft Advisory from 4 PM this afternoon to 10 AM PST Wednesday for PZZ271.

Small Craft Advisory from 10 AM this morning to 4 PM PST Wednesday for PZZ272-273.