textproduct: Portland

SYNOPSIS

A slow-moving frontal boundary will bring periods of light rain to southwest Washington and along the far north Oregon coast now through Monday morning, while the rest of Oregon stays dry with light winds and high clouds. A very strong high pressure system will strengthen and remain anchored over the Pacific Northwest Tuesday through next weekend. This will result in a prolonged stretch of dry weather with abnormally mild temperatures and light winds. Expect at least 6 to 8 consecutive dry days in a row.

DISCUSSION...Now through Saturday night

Aside from periods of light rain over portions of southwest Washington and the far north Oregon coast today through Sunday night/Monday morning, the weather forecast over the next seven days is highlighted by a prolonged stretch of dry and calm conditions with above normal temperatures for this time of year. This is in response to an anomalously strong high pressure system that models and their ensembles continue to suggest will remain locked in place through next weekend, while also becoming stronger Monday through Wednesday. This appears to be due to the development of an omega blocking pattern on the synoptic scale, resulting in warmer and drier conditions across the western U.S.

500 mb heights look to peak near 590 dm over northern California and southern Oregon, and near 585 dm over northern Oregon. Note these values are around the 99th percentile compared to climatology, which means high pressure of this magnitude is quite rare this time of year, especially given the extended duration. It is not clear exactly when the omega blocking pattern will break down and precipitation will return to the area, however some model guidance is beginning to hint on a potential pattern change back to wetter conditions Jan. 21-23. Until then, expect more of the same each day with varying degrees of cloud cover, light winds, and mild temperatures with afternoon highs running anywhere from 5-15 degrees above normal for this time of year depending on location. The NBM suggests highs will range between 50-60 degrees each day this week across the lowlands, except low to mid 60s in the Oregon Cascade foothills Tuesday through Saturday. The coolest daytime temperatures will occur in portions of the central and southern Willamette Valley where chances for fog and low clouds each night/morning may limit daytime heating and keep highs closer to 50 degrees. The reason the Oregon Cascade foothills will likely be warmest is due to a combination of more hours of sunshine and the fact that these elevations are high enough to poke above a strong low-level temperature inversion that will remain in place through the week, thus tapping into relatively warmer air aloft. Locations such as Oakridge will feel more like spring rather than mid January.

Overall, expect ideal conditions for outdoor work and recreation through the week. The only exception is for potential degraded air quality within the Willamette Valley due to a prolonged multiday stretch of stagnant air and very low vertical mixing heights, which helps trap air pollutants near the surface. State air quality agencies highly recommend that no outdoor burning occur and that residential wood burning devices be limited as much as possible. Check with your local burn agency for any current restrictions that may be in effect for your area.

People with respiratory illness should follow their physician's advice for dealing with high levels of air pollution during periods of stagnant air, especially if an Air Quality Alert is in effect for your area. To see if an Air Quality Alert is in effect for your area, go to www.weather.gov/pqr and left-click your location on the homepage map display. Alternatively, you could also type your location into the search bar found on the top-left hand side of the homepage. From there, you will see an Air Quality Alert listed at the top if one is in effect for your location; you can click the alert to read more details if applicable. -23

AVIATION

Westerly flow aloft will continue over the next 24 hours as high pressure dominates northwest Oregon. Meanwhile, a frontal boundary remains in place across southwest WA and the far north Oregon coast. This front will maintain periods of light rain at KAST through Sunday night/Monday morning while the remainder of Oregon stays dry. Winds will remain light throughout the TAF period, generally 5-10 kt or less. The main exception is at KAST where southerly winds will increase slightly late this afternoon with gusts up to 19-22 kt.

Main flight impacts will be associated with potential fog and low stratus within portions of the Willamette Valley Sunday night into Monday morning, however confidence is low regarding exactly where and when fog will develop. Similar to the past two nights, broken high clouds will be in place Sunday night with little change to the weather pattern. This setup has generally resulted in patchy fog and fluctuating visibilities at KHIO, KSLE, and KUAO. KHIO has the highest change for fog of any TAF site, with probabilities reaching 50% for surface visibilities below 1 SM by 09-12z Monday. Probabilities for fog range between 20-30% at KUAO, KSLE and KEUG. Otherwise expect VFR flight conditions to continue, except at KAST where MVFR cigs below 3000 ft become increasingly likely by 16z Sunday.

KPDX AND APPROACHES...VFR flight conditions are expected to continue through 12z Monday as high clouds continue. Light southeast winds throughout the TAF period, sustained between 5-8 kt. -23

BEACH HAZARDS

There is a high threat of sneaker waves at the coast through Monday due to a continued long-period southwesterly to westerly swell. Sneaker waves can create potentially life- threatening conditions as waves may run farther up the beach than expected. These waves can easily catch people off guard and cause beachgoers to be knocked off their feet and pulled out into cold ocean waters. Never turn your back to the ocean. Caution should be used when in or near the water, and those with children should be especially watchful. Sneaker waves can lift or roll large, heavy logs or rocks which can lead to serious death or injury. Keep off rocks, logs, and jetties near the waterline on beaches. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory until 4 AM PST Friday for ORZ109>111- 114>118.

WA...Air Stagnation Advisory until 4 AM PST Friday for WAZ205-206.

PZ...Small Craft Advisory until 4 PM PST this afternoon for PZZ210.

Hazardous Seas Warning from 4 PM this afternoon to 4 PM PST Monday for PZZ210.

Small Craft Advisory until 10 AM PST this morning for PZZ251-252-273.

Hazardous Seas Warning from 10 AM this morning to 4 PM PST Monday for PZZ251-252.

Small Craft Advisory until 4 PM PST Monday for PZZ253.

Hazardous Seas Warning until 4 PM PST Monday for PZZ271-272.

Small Craft Advisory from 10 PM this evening to 4 PM PST Monday for PZZ273.

Hazardous Seas Warning from 10 AM this morning to 10 PM PST this evening for PZZ273.