Marine Weather and Tide Forecast for Portland, OR

DISCUSSION
Tonight through Friday night...Satellite imagery and surface observations as of early Saturday morning depicts low stratus and fog developing across the Willamette Valley and southwest Washington lowlands. Dense fog has been patchy so far across these areas, with visibilities bouncing between 0.25 mile and 1.5 mile. Since fog with visibility of 0.25 mile or less has not been very widespread or long-lasting, have decided not to issue a Dense Fog Advisory for now. Will continue to monitor over the next few hours to see if that changes. If you will be commuting this morning, make sure to slow down, leave plenty of space between you and other vehicles, and use your low beam headlights.

An upper level ridge will continue to build over the Pacific Northwest this weekend bringing a return to drier conditions.
Should see increasing sunny skies by the afternoon with afternoon high temperatures likely warming into the lower 60s.
An offshore pressure gradient will also gradually increase easterly winds today, especially through the Columbia River Gorge and eastern Portland/Vancouver Metro Area. Latest guidance suggests the gradient from KTTD to KDLS peaks around -6 to -7 mb Saturday night into early Sunday morning, suggesting wind gusts up to 30-40 mph for the far eastern Portland/Vancouver Metro (Troutdale/Camas), and up to 60 mph for exposed ridgetops (e.g. Crown Point and Three Corner Rock). Offshore flow could make temperatures at the coast a degree or two warmer than the Willamette Valley this weekend. Slightly warmer conditions expected on Sunday as the ridge of high pressure amplifies into western Canada and persists over the region, shifting slightly eastward over the Great Basin.

Sunday night into Monday, the upper ridge begins to flatten as a shortwave trough pushes into British Columbia and NW Washington.
Since most ensemble guidance suggest that this system will track further north of our area, precipitation amounts are not looking significant or impactful. The highest chances for rain are along the coast and southwest Washington (60-80%), while chances for rain are lower (20-40%) across interior northwest Oregon. While the majority of ensemble guidance (75%) suggests rain arrives sometime late Sunday night into Monday, 25% of members do suggest rain arrives as early as Sunday afternoon along the coast. Chances for 0.25" of rain or more in a 24 hr period from 10 PM Sun to 10 PM Mon are only 20-40% along the coast (highest chances Tillamook northward) and 5-15% across the Willamette Valley and southwest Washington lowlands.

Another upper level ridge builds over the Pacific Northwest on Tuesday, bringing a brief return of dry weather. By Wednesday, this ridge quickly gets pushed eastward as another low pressure system over the NE Pacific progresses toward the Pacific Northwest. The majority of ensemble members (>80%) are in general agreement of light rain returning by Wednesday night as the cold front associated with the low swings through. Rain continues into Thursday, though there still remains some uncertainty with exact precipitation amounts and timing. For now, chances for 48 hour rain totals from 4 AM Wednesday to 4 AM Friday are around 60-80% along the coast, Coast Range, and Cascades, while chances are around 15-25% across interior lowland valleys. -10

AVIATION
Satellite imagery and terminal observations as of early Saturday morning depicts areas of LIFR/IFR VIS and CIGs across the Willamette Valley as patchy dense fog and low stratus begins to develop. Expect this mix of fog and low stratus to continue through 18z Sat with LIFR/IFR thresholds across most Valley terminals. An exception would be the far eastern Portland Metro including KTTD where easterly winds through the Columbia River Gorge would keep conditions more clear (less than 5% chance for fog). If easterly winds end up stronger, then KPDX could end up clearing as well. For now, not expecting easterly winds to be strong enough to clear out KPDX. An offshore pressure gradient will also bring easterly winds to the coast, keeping KAST and KONP predominately VFR through the TAF period.

Any fog or low stratus that develops this morning should begin to lift by 17-19z Sat as daytime heating progresses. VFR conditions return to the Willamette Valley by the afternoon with FEW/SCT high clouds as high pressure builds over the region.
Winds generally easterly to northeasterly, breeziest in the east Portland Metro with gusts up to 25-30 kt this afternoon.

KPDX AND APPROACHES...LIFR VIS/CIGs continue through 17-18z Sat as clear skies and light winds support patchy dense fog and low stratus development. Winds remain light and northerly early this morning, turning more easterly around 17-18z Sat. These winds will help clear out KPDX. Easterly winds gradually increase into the afternoon around 10-15 kt with gusts up to 20 kt. VFR conditions continue through the rest of the TAF period. -10

MARINE
A Small Craft Advisory continues across the waters through 10 AM Saturday morning as buoy observations as of early Saturday morning show seas around 12-13 ft at 11 sec. After 10 AM today, the westerly swell should ease below 10 ft. Another Small Craft Advisory has been issued for the Columbia River Bar today from 4-9 PM due to a very strong ebb resulting in seas of 7-9 ft at 12 sec.

High pressure building inland will drive offshore (easterly)
winds around 10 kt today before turning more southerly on Sunday as a weak front approaches the coast. Winds should remain minimally impactful through the weekend, with the chances for maximum gusts reaching 20 kt remaining below 5% south of Yaquina Head, increasing to 25% at Cape Lookout, to 50% at the mouth of the Columbia River, and further to 65% at the mouth of Willapa Bay. Meanwhile, seas ease to 4-7 ft by Sunday morning.

Winds vary through the first half of next week, but look to remain at 5-10 kt through Wednesday morning, and there is also high confidence (greater than 95% chance) that seas remain below 10 ft through midweek as well. An area of low pressure strengthening well offshore will see increasing southerly winds and a building southerly swell, increasing the chances for another period of conditions hazardous to small craft late Wednesday into Thursday. At this point, gale-force winds are not favored during this period, with 30-50% chances of occurrence beyond 20-30NM. -10/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.
WA...None.
PZ...Small Craft Advisory until 10 AM PST this morning for PZZ210- 251>253-271>273.

Small Craft Advisory from 4 PM this afternoon to 9 PM PST this evening for PZZ210.