Marine Weather and Tide Forecast for Rainier, OR

MORNING UPDATE
The first round of rain from this atmospheric river event as begun across the Pacific Northwest. Rainfall rates of 0.25-0.40" per hour have been observed this morning across the south Washington and north Oregon coast, Willapa Hills, and north Oregon Coast Range. There is high confidence that rainfall rates will hover between 0.25-0.50" per hour for much of today for these locations.
Rainfall rates this high will result in rivers and creeks draining off the Willapa Hills and Clatsop and Tillamook Counties to start rising sharply over the next 2 to 4 hours. -10

SHORT TERM
Today through Wednesday...The first of two major moisture surges is now underway this morning, with the main plume shifting into western Oregon and southwest Washington. IVT values today represent the strongest of the week, with ensemble clusters centering around 750 to 850 kg/ms near the coast and somewhat lower inland. This deep subtropical feed is producing widespread rain, and the spatial distribution continues to show a northward emphasis compared with several days ago. As a result, rainfall totals today will be highest north of Salem into southwest Washington, though most areas will see a substantial increase in runoff as rain falls on very saturated ground.

Expected rainfall today: 1.25 to 2.25 inches in the Cowlitz Valley, lower Columbia, Portland/Vancouver metro and northern Willamette Valley, 0.75 to 1.25 inches in the central Willamette Valley, and 0.25 to 0.75 inches in the southern Willamette Valley. Forecast rain amounts reach 3 to 7 inches in the Cascades, Cascade foothills, Coast Range and the coast, except 1 to 3 inches from Florence to Newport and in areas of higher terrain in Lane County. Snow levels remain well above 6000 ft, ensuring all precipitation is rain.

The second major moisture push arrives Tuesday night into Wednesday. This surge still carries impressive IVT (mean values around 650 to 750 kg/ms; high-end members approaching 800 kg/ms; low-end around 550 to 600 kg/ms), though slightly less vigorous than today’s event. Rainfall will remain heavy at times regardless, prolonging urban and river flooding concerns through midweek.

Wind concerns increase today and continue through Wednesday.
Monday is expected to be the windiest period, with widespread confidence in gusts reaching at least 30 mph inland and at least 40 mph along the coast. Given the soils are already saturated and heavy rain with gusty winds is expected, a Wind Advisory has been issued for potential impacts and will be in effect from 7 AM today through 4 AM Tuesday. The advisory covers the OR and WA Coast Range, Willamette Valley from Salem northward through the Portland/Vancouver Metro, I-5 corridor in WA, and the Cascade Foothills north of Salem. Soils are deeply saturated, increasing the likelihood that even moderate gusts could cause uprooting and damage. While confidence is high in potential impacts, confidence remains lower in pinpointing exact areas of greatest wind effects.

LONG TERM
Wednesday night through Saturday...The atmospheric river weakens late Wednesday night as the secondary plume shifts eastward and moisture transport diminishes. However, residual showers and pockets of moderate rain will persist through at least early Thursday, prolonging hydrologic sensitivity. By Thursday into early Friday, the pattern transitions toward a more typical post-frontal regime with cooler, showery conditions and decreasing winds. Light rain returns late Friday into Saturday. Snow levels will gradually lower into the weekend but remain high enough that little to no snow accumulation is expected for Cascades through the weekend.
Although overall impacts lessen late week, rivers and soils will continue responding to the cumulative rainfall load from this Monday through Wednesday multi-day event. ~12

HYDROLOGY
A series of frontal systems will keep conditions very wet through much of this week. The most notable period will be today through late Wednesday, when a prolonged atmospheric river will bring significant rainfall and the potential for widespread river flooding across southwest Washington and northwest Oregon. There is a 10% chance for 72 hour total rain amounts up to 6 to 8.5 inches in the Cowlitz Valley, lower Columbia, Portland/Vancouver metro and northern Willamette Valley, 4 to 6 inches in the central Willamette Valley, 3 to 4 inches in the southern Willamette Valley, 7 to 11 inches in the Cascades, Cascade foothills, Coast Range and the coast, except 3.5 to 7 inches from Florence to Newport and in areas of higher terrain in Lane County. While rain amounts this high are unlikely to occur, they represent a reasonable worst case scenario. This outcome would result in widespread major flooding.

Although rain will likely become lighter on Thursday, the threat of flooding will linger along slow responding rivers.
Rivers draining the Coast Range and Willapa Hills have a 40-70% chance of reaching moderate flood stage and a 20-50% chance of reaching major flood stage. Additionally, many Willamette River tributaries that drain from the Coast Range and Cascades have anywhere from a 40-60% chance of reaching minor flood stage and a 20-40% chance of reaching moderate flood stage. Flooding of the Willamette mainstem rivers have a very low chance to occur (5-15%). Probabilities for specific river points can be found at the National Water Prediction Service website.

There is also increasing confidence in the potential for flooding along small creeks and streams as well as urban flooding, including roadway flooding. Periods of heavy rain will also increase the risk for landslides in areas of steep terrain and debris flows over recently burned areas. People, structures, and roads located below steep slopes, in canyons, and near the mouths of canyons may be at serious risk from rapidly moving landslides. Therefore, a Flood Watch remains in effect across all of southwest Washington and northwest Oregon from now until 4 AM Friday.

Considering increased confidence and probabilities for flooding of rivers and urban areas as the forecasted event approaches, Flood Warnings have been issued for the Grays River at Covered Bridge in Wahkiakum County, the Wilson River near Tillamook in Tillamook County, and Johnson Creek at Sycamore in Clackamas and Multnomah Counties.

Major flood stage at the Grays River is forecast, which will lead to flooding of lowland areas and roads in the vicinity of Highway 4 and Rosburg. there will be two peaks for this river. There is high confidence that the first peak will occur between 1 AM to 4 AM Tuesday. The river will briefly subside between 4 AM to 10 AM Tuesday, but a second round of heavy rain will result in another peak late Tuesday into Wednesday. For the Wilson River, Minor flood stage is forecast from late tonight to late Wednesday morning, and for Johnson Creek, Minor flood stage is forecast from Tuesday morning to Wednesday evening. Both the Wilson River and Johnson Creek have a 50% chance of reaching Major flood stage. If you know you live in a flood-prone area, make sure to monitor the latest weather and river forecasts, and make a plan for potential impacts.

AVIATION
A moisture-rich frontal system will bring increasing south to southwest winds across the area today along with a band of steady rain that will slowly sag southward from northwest Washington this morning into southwest Washington and most of northwest Oregon by late morning. Rain will likely take a bit longer to begin at KEUG. Rain will be heavy at times through the period, lighter around KEUG. This will result in persistent low-end MVFR cigs with brief periods of high- end IFR cigs for inland TAF sites, as well as surface visibility reductions down to 2-4 SM at times. Meanwhile, persistent LIFR to IFR flight conditions are favored to at the coast through 12z Tuesday, except through 09z Tuesday at KAST where cigs will begin lifting to MVFR or low- end VFR thereafter.

Surface wind gusts up to 35-40 kt are expected at the coast, and up to 25-35 kt within the Willamette Valley. In addition, low level wind shear will be on the increase at KPDX, KTTD and KAST Monday morning with 45-55 kt southwest winds at 2000 ft. Note the main concern is strong speed shear, as winds are nearly unidirectional from the surface up to 4000 ft, suggesting directional shear will be minimal.

KPDX AND APPROACHES...Expect mainly low-end MVFR cigs to continue through 12z Tuesday with a 20-30% chance for cigs to briefly fall below 1000 ft cigs Monday morning. Steady stratiform will persist through the period, becoming moderate to heavy at times through the afternoon. It appears rain will briefly become lighter again Monday evening before intensifying again Monday night. Expect surface visibilities down to 2 to 4 SM when rain rates are highest. Wind gusts up to around 30-35 kt are expected Monday afternoon through Monday night. Note there will also be a period of increased low- level wind shear Monday morning as winds at 2000 ft reach 45-55 kt out of the southwest. The main concern will be strong speed shear, as directional shear looks minimal. -19/23

MARINE
A stronger frontal system is set to arrive early Monday, bringing gale force wind gusts up to 35-45 kt, strongest over the inner waters and near the Columbia River Bar. A Gale Warning is in effect through 1 AM Tuesday as probabilities for gale force gusts are up to 90%. With the increasing winds, seas will become steep and hazardous Monday afternoon into Monday night.
Expect seas to peak somewhere between 14 to 17 ft.

Winds decrease from north to south late Monday night into Tuesday morning with gusts falling below 20 kts everywhere except for portions of zones PZZ273 and PZZ253 briefly on Tuesday morning.
Then another frontal system moves through the waters Tuesday afternoon into Wednesday, causing increasing southwesterly winds with gusts up to 25-30 kt likely. There's around a 20% chance of occasional gale force wind gusts over 34 kts across the waters Tuesday night, though widespread gale force gusts are not expected for a long enough period of time. One potential exception will be the inner waters, which have a 30-45% chance of marginal gale force wind gusts up to 35 kt. Seas also decrease slightly Tuesday into afternoon Wednesday but remain above 10 ft. Seas and winds subside late in the week. -23/03

BEACH HAZARDS
Tidal overflow flooding around high tide is likely on Monday, December 8 and possible on Tuesday, December 9.
Despite total tide forecasts decreasing over the coming days, river levels will be rapidly rising due to a prolonged period of heavy rain Monday through Wednesday. Confidence has increased that several rivers along the Oregon Coast north of Lincoln City and the SW Washington Coast will reach at least 80% of flood flow by high tide Monday afternoon, when total tide forecasts are expected to peak near or slightly above 9.5 ft. Therefore, a Coastal Flood Advisory for tidal overflow remains in effect from 2 PM to 6 PM PST Monday for these coastal zones. It appears the threat for tidal overflow flooding is low on Tuesday, as total tide forecasts decrease considerably and are well below the 9.5 foot threshold.
That said, minor tidal overflow flooding cannot be completely ruled out for a brief period of time around high tide on Tuesday given river levels will be running quite high at that time. Will continue to monitor the tidal and river forecasts for Tuesday.

Additionally, there is an elevated threat for sneaker waves late Wednesday through Thursday along the SW Washington coast south through the central Oregon 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. This will create energetic waves that will present a moderate to high risk for sneaker waves, waves which can run significantly farther up a beach than normal, including over rocks and jetties. Sneaker waves can suddenly knock beachgoers off if 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. -23/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...Coastal Flood Advisory from 2 PM this afternoon to 6 PM PST this evening for ORZ101-102.

Wind Advisory until 4 AM PST Tuesday for ORZ104>115-123.

WA...Coastal Flood Advisory from 2 PM this afternoon to 6 PM PST this evening for WAZ201.

Wind Advisory until 4 AM PST Tuesday for WAZ202>208.

PZ...Gale Warning until 1 AM PST Tuesday for PZZ210-251-271.

Small Craft Advisory from 1 AM to 7 PM PST Tuesday for PZZ210- 251-271.

Gale Warning until 7 AM PST Tuesday for PZZ252-253-272-273.

Small Craft Advisory from 7 AM to 7 PM PST Tuesday for PZZ252- 253-272-273.