textproduct: Portland

SYNOPSIS

Light to moderate rain persists across southwest Washington and the north Oregon Coast Range early this morning, keeping several rivers elevated as runoff continues to work through the system. A gradual improvement in conditions is expected later today into Friday as an upper ridge begins to build. A quieter stretch of weather follows Friday and Saturday before the next organized frontal system approaches late Saturday night into Sunday. A stronger and wetter system is then anticipated early next week.

DISCUSSION...Now through Tuesday

Lingering moisture on the southern flank of the weakening atmospheric river continues to support areas of light to moderate rainfall across southwest Washington and portions of the north Oregon Coast Range. Expected precipitation rates generally remain at or below one tenth of an inch per hour, though there is still a modest chance for brief increased rates over higher terrain. While these rates are not expected to produce new flooding concerns, they will delay recession on rivers that remain high from earlier rainfall. Farther south, conditions across northwest Oregon are mostly quiet aside from patchy showers and persistent cloud cover. Snow levels remain high, around 7500 to 8500 feet, keeping the Cascades predominantly in rain except at the highest volcanic summits. Winds are gradually diminishing early this morning following a breezy period, with gusts now mostly below advisory levels for all but the Columbia River Gorge and a few exposed ridgetops.

A more notable improvement in weather is expected later today into Friday as an upper ridge strengthens over the region. Shower coverage will steadily decline, and many locations will see extended breaks from precipitation beginning Friday. Partial clearing is possible by Friday morning, which may support areas of fog or low stratus through the day and into Saturday morning. Better clearing is anticipated Saturday afternoon as the ridge shifts overhead.

The next frontal system approaches the region Saturday night into Sunday, bringing increasing cloud cover and renewed chances for rain. Current ensemble guidance suggests modest precipitation amounts with this initial front, with the higher totals most likely along the coast, Coast Range, and southwest Washington (24 hour rain totals from 10 PM Sat to 10 PM Sun: 0.3-0.5 inch around the coast, Coast Range, and southwest Washington and under 0.2 inch elsewhere). Snow levels briefly dip to around 6000 to 7000 feet, keeping pass-level precipitation as rain.

A more robust and wetter system follows early next week, around Monday. Confidence is increasing that this system will produce heavier rainfall across southwest Washington, the Coast Range, Willapa Hills, and the Cascades, with lower amounts extending into the interior lowlands. Given how saturated the soils are at the moment, even moderate additional rainfall may lead to renewed sensitivity of rivers and streams. Breezy winds are also likely with this system, particularly along the coast. Current guidance suggests wind gusts around 30 to 35 mph inland and 45 to 50 mph at the coast on Friday. Worst case scenario (10% chance of occurring), winds could gust up to 40 to 45 mph inland and 55 to 60 mph along the coast. Given the spread, details regarding magnitude and timing of winds remains uncertain and warrants monitoring as early next week nears. ~12

HYDROLOGY

Rivers across southwest Washington and the north Oregon Coast Range remain elevated early this morning due to ongoing light rainfall and continued runoff from earlier precipitation. Flood Warnings remain in effect for the Grays River near Rosburg, the Cowlitz River at Kelso, and the Luckiamute River near Suver. While the Pudding River near Aurora is not forecasted to reach minor flood stage, it remains in action stage early this morning, very close to minor flooding. As a result, we will continue to closely monitor the Pudding River, especially as as runoff continues to drain into this river. Each river is responding at a different rate, with some having crested and others still rising or leveling off, but all are expected to remain elevated into the latter half of the week.

AVIATION

A stalled frontal boundary remains oriented west to east over southern Washington. Flow remains westerly with most of the moisture remaining north of the boundary. However, there is still some moisture in the area, supporting light scattered showers through into the afternoon. Conditions are mainly MVFR with CIGs between 1500-3000 feet inland and IFR along the coast. Showers are expected to taper off this afternoon as the front shifts slowly to the north. This will lead to cloud cover breaking up a bit this afternoon, this is already evident over the southern Willamette Valley where KEUG is reporting VFR conditions.

High pressure develops Thursday evening/night, bringing calm winds and some clearing Thursday night. This will set the stage for widespread fog and low stratus develop across inland valleys, including all inland TAF sites. Probabilities for surface visibilities below 1 SM peak between 50-70% by 12z Friday, with cigs likely falling below 500-1000 ft.

KPDX AND APPROACHES...Mainly MVFR conditions with scattered showers continuing through the afternoon. Fog and/or low clouds will attempt developing over or near the terminal by 11-12z Friday. This is when there is a 50% chance for surface visibilities at or below 1/2 SM with cigs falling below 1000 ft. -19/23

MARINE

Small craft advisories remain in effect through 1 PM Thursday across the coastal waters, including the Columbia River Bar. Although winds have fallen below 10-20 kt, seas remain around 10-11 ft at 13 to 15 seconds and will be hazardous to small craft. Seas are expected to fall below 10 ft by mid to late Thursday afternoon and should then stay below 10 ft through Sunday, marking a prolonged stretch of relatively benign conditions. One exception is Saturday evening through Sunday morning when marginal small craft advisory level wind gusts up to 25 kt have a 90% chance of occurring with a frontal passage.

This front will mark the beginning of a more active weather pattern for the upcoming week. Main concerns begin early Monday when a stronger front traverses the coastal waters, bringing hazardous seas and increasing winds. There is high confidence for southerly gale force wind gusts by Monday afternoon with this front, as probabilities are near 90% for max wind gusts over 34 kt between 10 Sunday and 10 PM Monday. Hourly probabilities are also high, especially over the inner waters. Storm force wind gusts over 48 kt cannot be ruled out either, as probabilities range from around 20% over the outer waters and near 40% chance over the inner waters. Probabilities are highest over the inner waters due to the development of a potential coastal jet. Guidance suggests seas will most likely peak somewhere between 15-20 ft Monday afternoon and evening, however the outcome will be highly dependent on wind speeds and how high wind waves are able to build. While unlikely to occur, there is a 5% chance significant wave heights will peak anywhere between 21-25 ft, which represents the worst case scenario. Note seas and winds will remain elevated Tuesday into Wednesday as well, albeit not quite as high as Monday. -23

BEACH HAZARDS

There remains an elevated threat for sneaker waves through Thursday along the entire coast. The swell period increases to around 14-15 seconds with swell heights around 9-11 ft, with swell heights and swell periods decreasing late Thursday night into Friday. This will create energetic waves that will present a moderate to high risk for sneaker waves, which are waves that can run significantly farther up a beach than normal, including over rocks and jetties. Sneaker waves can suddenly knock beachgoers 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. Always keep an eye on the waves, and be especially watchful of children. -23/99

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 1 PM PST this afternoon for PZZ210- 251>253-271>273.