textproduct: Portland

SYNOPSIS

A Pacific frontal system will bring light rain back into the area early Sunday morning with mild temperatures continuing. Trending mainly dry Sunday night. Light rain likely returns to southwest WA and far northwest OR on Monday. High confidence for a prolonged period of dry weather and above normal temperatures Tuesday through at least Friday as a strong upper level ridge develops over the region. Some uncertainty remains regarding how long this ridge will persist and when precipitation will return.

LONG TERM...Tuesday through Friday night

The long term forecast is highlighted by dry weather, warmer than normal temperatures, and breezy easterly winds in the western Columbia River Gorge and far eastern Portland/Vancouver metro. This is in response to a strong upper level ridge that will remain locked in place from Tuesday through at least Friday. In fact, the LREF ensemble mean suggests 500 mb heights will reach the 97-99th percentile compared to climatology, meaning this ridge is abnormally strong for this time of year. As such, confidence is high Tuesday through Friday will be dry. In addition, widespread high temperatures in the 50s and 60s are forecast each day with the coolest temperatures in valleys and warmest temperatures in the Cascades/foothills due to a persistent temperature inversion. The coast will also trend quite warm for this time of year given the offshore flow in place, with forecast high temperatures well into the 60s along the central Oregon coast and around 60 degrees along the north Oregon and south Washington coast.

Although confidence is high it will be dry with much warmer than normal temperatures for the coast, Coast Range and Cascades/foothills, confidence is lower regarding how expansive/persistent low stratus will be within the Willamette Valley and the impact that will have on temperatures, especially the central/southern valley. Meteorological set-ups like this one tend to favor stubborn low stratus in the Willamette Valley, which keeps temperatures much cooler compared to higher elevations that are poking above the stratus layer and into warmer air aloft. Model guidance tends to handle low stratus poorly with this type of set-up, especially in the long term when hi-res model guidance is not available. For now, it appears Tuesday and Wednesday have higher chances for low stratus to persist over portions of the Willamette Valley during much of the the day when compared to Thursday and Friday which are trending sunnier for all locations. The sky cover and temperature forecast for next week will likely need some refinement over the coming days as these details become clearer, at least within the Willamette Valley where uncertainty is highest. Regardless of the outcome, some locations will be in the running for record high temperatures at some point next week, especially where skies end up mostly sunny through the day.

It is also worth mentioning that air stagnation concerns will increase in the Willamette Valley next week, which may lead to degraded air quality over time, especially in the central and southern Willamette Valley. Meanwhile, portions of the northern Willamette Valley and Portland metro will have an offshore flow influence, with easterly winds becoming gusty at times in the eastern Portland/Vancouver metro and western Columbia River Gorge (but generally under 30-40 mph with minimal impacts). -23

AVIATION

Predominately VFR conditions under southwest flow aloft. Winds across the area are light and variable except for locally elevated east winds through the western mouth of the Columbia River Gorge with gusts up to 25 kts. These winds should decrease after 06z Sun. Ahead of an incoming front, there's a 25-50% chance of fog/low stratus developing again between 02-15z Sun in the Willamette Valley, especially terminals KHIO, KUAO, and KSLE.

A frontal system is forecast to begin pushing east into the region after 06z Sun. Widespread rain showers will push inland ahead of the front, beginning along the coast sometime between 06-10z Sun, spreading to inland terminals by 12-15z Sun. There's a 60-80% chance of MVFR/IFR ceilings at coastal terminals behind the front and a 30-50% at inland terminals, best chances in the central and southern Willamette Valley. Terminals that develop fog earlier on Sunday could see continued lower visibilities before the rain mixes out the fog, with conditions lifting to MVFR/IFR. Winds will turn southerly and increase behind the front. Expect south winds around 10-15 kts with gusts up to 20 kts along the coast after 12z Sun and south winds around 10 kts after 13-15z Sun for inland terminals.

KPDX AND APPROACHES...VFR conditions with light and variable winds into Saturday night. A frontal system approaches early Sunday morning with rain showers beginning between 13-15z Sun. Winds become southerly at this time, increasing to around 10 kts. There's a 30-50% chance of MVFR/IFR ceilings after 15z Sun. -03

MARINE

South winds will increase ahead of and along a surface front as it slowly approaches and moves through the waters Saturday night into Sunday morning. This is not expected to be a particularly strong front with sound winds 15-20 kts with gusts up to 20-25 kts, gusts decreasing below 20 kts late Sunday afternoon. Another weak front will graze the waters late Sunday into Monday, with another quick increase in south winds with gusts 20-25 kts, decreasing below 20 kts by late Monday afternoon. A decaying westerly swell is producing wave heights around 7-9 ft at 11 seconds Saturday afternoon. However, a fresh, persistent westerly swell associated with the two incoming surface fronts moves into the waters tonight, continuing through Monday. This is expected to increase wave heights to 10-13 feet at 11-13 seconds with the period increasing to 14-15 seconds late Sunday into Monday. Due to a combination of winds and seas, a Small Craft Advisory is in effect through 4 PM PST on Monday.

High pressure builds over the waters Tuesday with southerly winds less than 10-15 kts and seas less than 10 ft. By Wednesday, high pressure persists keeping winds calmer, but an increasing westerly swell is forecast to push into the waters, increasing seas to around 10-12 feet around 12-15 seconds through the end of the week. -03

BEACH HAZARDS

A long period westerly swell will result in a high threat for sneaker waves persisting through Monday afternoon. 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 this week. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 4 PM PST Monday for PZZ210-251>253- 271>273.