Marine Weather and Tide Forecast for Clatskanie, OR

DISCUSSION
Wednesday afternoon through Tuesday...Widespread precipitation moved through NW Oregon and SW Washington this morning associated with the frontal system impacting the PacNW.
Conditions have become showery this afternoon as the front has moved into eastern OR and WA. Wind gusts up to 25-30 mph were observed over the area with localized gusts up to 40-45 mph over the terrain and coast as the front passed this morning. Expect winds to slowly decrease this afternoon everywhere except for the terrain where gusts continue into Thursday. The post-frontal environment is becoming convective as visible satellite imagery shows periods of clearing followed by cumulus cloud development.
Model soundings still suggest skinny CAPE soundings with CAPE values up to 100-200 J/kg through the early evening hours today, leading to a 10-25% chance of isolated thunderstorms.
With CAPE this low, not expecting widespread thunderstorms, but periodic stronger showers that could produce brief gusty winds, small hail, or heavy rain/mountain snow with one or two becoming strong enough to produce lightning. Snow continues over the Cascades above 3500-4000 ft into early Thursday morning.
Heaviest snow expected through this evening above 4000 ft. An additional 6-11 inches of snow is possible through 4 AM Thursday at Santiam and Willamette passes, though with the showery nature of precipitation amounts could fall above or below this range depending on where individual showers set up. Due to the convective nature, heavier showers could also produce snowfall rates up to 1 inch per hour at times through around 9 PM tonight.

High pressure builds over the eastern Pacific Thursday into the early weekend, though the PacNW remains on the eastern periphery of the flow. This will allow moisture to continue streaming into the area from the north. Scattered showers continue Thursday into Friday with fairly benign accumulations expected. Snow levels continue falling late tonight into Thursday to around 2500-3000 ft, though accumulation is expected to be very limited below 3500 ft. As the high pressure builds, so do the snow levels rise to above pass level on Friday. Expect daytime temperatures for the interior lowlands to peak in the upper 40s on Thursday, warming a few degrees to the low 50s by Friday.

Ensemble guidance suggests high pressure will spread inland on Saturday, allowing temperatures to warm even more into the mid to upper 50s. Dry weather is likely for the interior valley as well as the Coast Range and Cascades near and south of Highway 20. However, dry weather will be short lived as a shortwave moving east through British Columbia causes the flow to become zonal over the PacNW on Sunday, allowing the return of moisture and therefore scattered showers Sunday into Monday. Daytime temperatures on Sunday will be similar to Saturday, but latest guidance suggests a 5-10 degree drop on Monday as colder air from Canada begins pushing south into SW WA and NW OR.
Uncertainty remains on timing of this push and how far south the cold air will make it, but latest guidance indicates that at least 75% of the GEFS, EPS, and GEPS members bring 850mb temperatures below -5 deg C by late Monday night/early Tuesday morning to the Portland area. Latest NBM guidance has a 50-70% chance for low temperatures to fall to or below freezing for Tuesday morning's low temperature across the lowlands. With temperatures this low along with shower chances continuing into Tuesday, NBM is indicating a 30-45% chance of at least a rain/snow mix Tuesday morning down to the valley floor for the Portland/Vancouver metro area and north through the Cowlitz valley. Looking at probabilities for at least 1 inch of snow, this drops to around 5-15% for locations below 1000 ft elevation, with around 40-60% chance for elevations between 1000-2000 ft elevation. This is definitely a pattern we will be keeping our eye on as the forecast unfolds. -03

AVIATION
Showery precipitation continues behind the cold front with activity persisting into the overnight hours. Increased instability behind the front will lead to a 15-25% chance for thunderstorms across the area through 00z Thu, with the highest chances over the southern Willamette Valley (KEUG). Any passing thunderstorms may bring lightning, brief heavy downpours, erratic winds, and/or small hail. Southwesterly winds today with gusts up to 25 kt along the coast and 20 kt across the Willamette Valley.
Showers chances decrease through the night and sub-VFR CIG probabilities trend lower. There is still a 40-70% chance of MVFR CIGs along the coast through Thursday morning and a 10-40% chance throughout the Willamette Valley at any given hour for the same time period.

KPDX AND APPROACHES...VFR CIGs are expected through most of the TAF period with a 10-40% chance of MVFR CIGs any hour through Thursday morning. Shower activity continues overnight but will decrease through Thursday morning. 15-20% chance for thunderstorms through 00z Thu. Southwesterly winds 5-10 kt with gusts up to 20 kt possible. -19/10

MARINE
Breezy southwest winds will gradually turn more northwesterly through the evening with wind gusts up to 25 kt expected through 4 AM. Winds are expected to decrease Thursday morning. Seas around 7-9 feet at 7-9 seconds will increase to around 10-11 feet at 10-12 seconds overnight, leading to steep seas and continued hazardous conditions for Small Craft through Thursday. High confidence for calmer marine conditions behind this system at the end of the week and into the weekend, with seas falling below 10 feet and winds turning more westerly and remaining under 15 kt by Thursday afternoon. -19

PQR WATCHES/WARNINGS/ADVISORIES
OR...Winter Weather Advisory until 4 AM PST Thursday for ORZ127-128.
WA...None.
PZ...Small Craft Advisory until 4 PM PST Thursday for PZZ210- 251>253-271>273.