Marine Weather and Tide Forecast for Stevenson, WA

SHORT TERM
Now through Friday Night...There has been minimal change to the short term forecast with today's update as the weather pattern in place remains persistent. The two significant synoptic scale features at play are a broad upper level ridge centered over the U.S. Desert Southwest and a broad trough over the Gulf of Alaska, maintaining persistent west to southwest flow aloft over the Pacific Northwest. Between these two features is a weakening atmospheric river embedded within the persistent southwesterly flow.
As of 2 PM PDT Wednesday, radar and satellite observations depicted a narrow band of light stratiform rain around 50-100 miles wide within the axis of greatest moisture transport. This band of rain was mainly impacting Pacific County, Wahkiakum County, and northern portions of Cowlitz and Skamania counties. Hi-res model guidance suggests this band of rain will occasionally shift to the south and north, impacting the far north Oregon coast at times through Thursday night.
As such, these areas will remain cloudy and cooler while the rest of northwest Oregon remains partly to mostly sunny with warmer high temperatures in the upper 60s to mid 70s, except mid 50s to mid 60s along the coast. The warmest temperatures are expected over the central and southern Willamette Valley and the Cascade foothills; note recent surface weather observations show relative humidities falling into the 20-40% range or lower in these areas during peak daytime heating. This means humidity levels are low and the airmass remains quite dry to the south of the aforementioned band of rain.
The NBMv5.0 was utilized to help lower the relative humidity forecast in these areas.

Come Friday, conditions should become more moist with relatively cooler temperatures as the band of rain focused over southwest Washington finally shifts southward as a cold front across northwest Oregon, albeit decaying at the same time. This will result in increasing clouds on Friday with high temperatures generally in the mid 50s to mid 60s, coolest north of Salem and warmest south of Salem. There is also a 50-80% chance of light rain showers on Friday as the cold front moves through, with the highest probabilities in the mountains late in the day. Rain amounts are expected to be light and insignificant with no notable impacts to discuss. In fact, some locations will likely only see trace amounts of rain, especially over the central and southern Willamette Valley. Showers should begin to decrease in coverage Friday night. -23

LONG TERM
Saturday through Wednesday...The long term forecast remains highlighted by a relatively cooler weather pattern with seasonable temperatures and mainly dry conditions, except Tuesday and Wednesday when wetter conditions arrive. For the Saturday through Monday time frame, models and their ensembles are in good agreement for nearly zonal flow aloft with surface high pressure in place over southwest Washington and western Oregon. This will result in mainly dry conditions during that time, however there may be isolated post-frontal rain showers lingering on Saturday, mainly over the mountains early in the day (30-60% chance).

Attention then turns to the Tuesday to Wednesday time frame. This is when ensemble guidance depicts the arrival of a stronger Pacific cold front, bringing wetter conditions with widespread rain. NBM probabilities for precipitation pick up on this well and peak between 80-90% by Tuesday evening/night. Although confidence is high precipitation will return, confidence is not as high regarding exact precipitation amounts as model spread for QPF is large. The NBM 10th percentile for 48-hour QPF amounts from 5am Tuesday to 5am Thursday ranges from around 0.10-0.50 inches, while the NBM 90th percentile ranges from 1.00-3.50 inches (highest amounts at the coast and across the western slopes of the Coast Range and Cascades). Regardless of the exact outcome, it appears flooding will not be a concern. Another aspect of the forecast on Tuesday and Wednesday that has high uncertainty is snow levels. The NBM 10-90th percentile for snow levels during that time ranges from 2000-9000 feet, respectively. The most likely outcome is around 5500-8000 feet, highest over the Lane and Linn County Cascades and lowest over the south Washington Cascades. As such, is not clear yet whether or not the Cascades will see rain, a rain/snow mix, or accumulating snow. It is also not clear yet if the Cascade passes will be impacted with accumulating snow.
Probabilities for 6 inches of snow or more in a 48-hour period ending at 5am Thursday are quite low as pass level (10-15%). This seems reasonable as only the coldest ensemble guidance suggests snow levels will fall low enough for impactful snow amounts at pass level. Also worth noting is breezy south to southwest winds with the frontal passage on Tuesday, albeit likely staying below 35 mph with minimal impacts. -23

AVIATION
An upper level ridge to the south and a broad upper level trough over the Gulf of Alaska continues to squeeze an atmospheric river, continuing light rain over the north Oregon and south Washington coast. Expect this light rain to become showery into tomorrow morning. For coastal terminals, expect a mix of MVFR/IFR conds through the TAF period, with an exception of possible LIFR conds at KONP before 18Z Thu, improving to VFR thereafter (20-40% chance of LIFR; 40-60% chance of IFR). As for inland terminals, expect VFR conds and high clouds through the TAF period.

Through the TAF period, winds will remain generally southerly and under 8 kt. One exception, terminals along the Columbia River will vary from southerly to southeasterly, while the rest of the Willamette Valley will see southerly to southwesterly winds. Could see gusts up to 20 kt at coastal terminals during the afternoon around 18-23Z Thu.

KPDX AND APPROACHES...VFR conditions and high clouds continue through the TAF period. Southerly to southeasterly winds under 10 kt.
~12

MARINE
Low pressure offshore will maintain breezy southerly winds through Thursday, mainly for the waters north of Cape Falcon including the Columbia River Bar. A Small Craft Advisory has been issued for these areas through 5 PM Thursday for southerly winds 15-20 kt with gusts up to 25 kt. Winds remain weaker south of Cape Falcon. Swells are forecast out of the southwest and northwest, with combined wave heights around 7-9 ft at 10-11 sec through Friday. High pressure builds this weekend, turning winds more northerly and remaining under 20 kt. Seas then gradually fall to 5-7 ft at 10-11 sec. Benign marine conditions continue through Monday before another system returns Tuesday- Wednesday. Guidance suggests a 50-60% chance for widespread, small craft wind gusts of 21 kt or greater on Tuesday. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.
WA...None.
PZ...Small Craft Advisory until 5 PM PDT Thursday for PZZ210-251-271.