Cape Shoalwater WA to Cape Lookout OR between 60 and 150 NM Offshore Forecast
|Today...W Winds 20 To 25 Kt, Becoming Nw 15 To 25 Kt. Seas 8 To 14 Ft. Rain.|
|Tonight...Nw Winds 20 To 25 Kt. Seas 12 To 16 Ft.|
|Mon...N To Nw Winds 20 To 25 Kt. Seas 13 To 16 Ft.|
|Mon Night...N Winds 15 To 20 Kt, Becoming N To Nw 10 To 15 Kt. Seas 10 To 13 Ft.|
|Tue...W To Nw Winds 5 To 10 Kt, Becoming Sw 15 To 25 Kt. Seas 8 To 10 Ft.|
|Tue Night...Sw Winds 25 To 35 Kt. Seas 8 To 14 Ft.|
|Wed...W Winds 15 To 25 Kt. Seas 13 To 15 Ft.|
|Wed Night...W To Nw Winds 10 To 20 Kt, Becoming Nw 5 To 10 Kt. Seas 12 To 15 Ft.|
|Thu...N To Nw Winds Less Than 10 Kt. Seas 10 To 13 Ft.|
|Thu Night...N Winds 10 To 15 Kt, Becoming 10 To 20 Kt. Seas 7 To 12 Ft.|
| Area Forecast Discussion|
...UPDATED National Weather Service Portland OR
843pm PST Sat Nov 26 2022
Updated Aviation Section
The strengthening cold front will drop down from the Gulf of Alaska this afternoon bringing widespread rainfall and Cascade Snow. A Winter Storm Warning is in effect for the Cascades through Monday. More active, but complex weather returns mid-week with chances for lowland snow.
.SHORT TERM /THROUGH TUESDAY/...Satellite imagery shows the initial stages of the cold front moving southeast from the Gulf of Alaska. While still well offshore, the frontal boundary will move inland by this evening starting the rainfall along the north Oregon/south Washington coast. This front has been well realized for the last several days so confidence is high that we will see widespread low elevation rain and snow across the Cascades. Initially the heavy snow will start over the Washington Cascades early Sunday morning and will spread southward as the main body of the front advances inland. Ensembles show the highest accumulations in the north and central Oregon Cascades with the heaviest period of snow falling from Sunday afternoon into early Monday morning. The NBM forecasts around a 95% chance of exceeding 12 inches of snow in 24 hrs, and around 80% of exceeding 18 inches along the highest peaks and mountains. Given the high volume of travelers on Sunday and these snow amounts, have continued the Winter Storm Warning through Monday afternoon. Snow will ease from north to south through the day on Monday. In addition to this snow, will likely see higher wind speeds with gusts exceeding 35 mph in the Cascades, and around 20 mph in the lowlands. Any blowing snow could reduce visibility at times.
Meanwhile, elevations below 2500 ft will mostly see rain through the bulk of the upcoming event, with Quantitative Precipitation Forecast amounts ranging from 0.75-1.00 inch at the coast and closer to a half inch in the Willamette Valley. Regarding lowland snow, the probability has shifted even lower. While there is still a non-zero chance for snow, temperatures appear too warm to have any snow manifest. The areas that may see rain/snow mix (predominately rain though) would be those areas between 1000-2500 ft in the foothills. Conditions will transition from stratiform precipitation to more showers behind this fast moving front. Accumulations will dwindle, but where these showers develop, will see heavier accumulations or rain and/or snow. There remains a slight chance of thunder over the waters and the coastline behind the front.
Tuesday will bring isolated post-frontal showers with no impactful weather. However, it will be the transitional day prior to a much more active mid-week. To set the stage, on Tuesday, an elongated trough of cold air will seep southward over the Rockies. This cold air pool will come into play on Wednesday. In the meantime clearing skies overnight with light winds could bring patchy frost to Columbia, Clark, Washington and Multnomah Counties. -Muessle/CB
/WEDNESDAY THROUGH FRIDAY/...There remains high uncertainty in the long term forecast, but there are some more predominate trends. The overall pattern is consistent of a low pressure system moving down the Alaska Panhandle and the British Columbia coast late Tuesday into Monday. In previous runs, this low was deepening into the 980-990 mb range, while most recent runs of the GFS (Global Forecast System) show it closer to 1000 mb by time it reaches Oregon. This is the telling sign that there is some evolution of the system. In addition, models appear to have 'backed off' of the strong pool of cold air to the east. While it will still be cold, the easterly winds previously expected from this deep low will be weakened and thus, less cold air will filter into the lowland areas. 850 mb temperatures too have been altered just slightly with this front. On the leading edge, will see temperatures around -0.5C, and behind around -6C by Thursday afternoon. These temperatures are not nearly as cool as they once were. Combine the lack of consistently in temperatures with the variability of precipitation timing and accumulation, there remains high uncertainty in the long term.
Aspects of the forecast that include high certainty are: Cascade snow from Wednesday through Thursday, some of the coldest temperatures seen thus far this season late in the week, lowering snow levels, and widespread precipitation. Low confidence components include: the possibility of lowland snow, how low the snow levels will drop to, and snow accumulations along the Cascades. Based on the projected precipitation amounts and ensemble guidance, there is around a 70% chance of seeing greater than 8 inches of snow along the Cascades above 2500 ft, and around 40% chance of 12 inches of snow above 4000 ft. Snow levels too will drop, although those have slightly raised in comparison to previous model outputs. The big question on people's minds though is "will we get snow below 1000 ft"? The answer...maybe. There are a lot of components feeding into the possibility for lowland snow on Wednesday into Thursday; the main of which includes the timing of the precipitation to the cold air. As it stands, there is around a 30% chance of seeing some accumulating snow (greater than 0.1 inch) below 1000 ft; this also means there is a 70% chance that we will not see any snow accumulations at those elevations. Will continue to track this system as it evolves over the next few days. -Muessle
A brief break in the weather is ongoing right now, but will be replaced by a cold front dropping southeastward across the waters tonight. Seas continue to hover around 10 ft early this evening, but should gradually subside by late this evening. Given winds and seas will be on the increase later tonight ahead of the cold front, kept the Small Craft Advisory in effect even though conditions will likely be below Small Craft thresholds for a 4-8 hour period overnight. Expect occasional gusts of 25 to 30 kt Sunday into Monday and seas to generally hover in the 10-14 ft range. Weak high pressure shifts across the waters Monday night, but a developing low pressure moving towards the Strait of Juan de Fuca Tuesday into Wednesday will result in increasing southerly winds across the waters during this time. Most ensemble guidance suggests high end Small Craft to low end Gale Force wind gusts of 30 to 35 kt developing across the waters by Wednesday. Seas should climb back into the teens as a result. Additional storm systems appear possible late in the work week.
The new moon phase this weekend will produce stronger tidal currents during the evening ebb cycles. Those moving in and out of harbors and crossing coastal bars should use extra caution and be aware of any bar restrictions in place. /Neuman
NOAA Portland OR Office: Watches - Warnings - Advisories
OR...Winter Storm Warning from 4am Sunday to 10am PST Monday for Northern Oregon Cascades.
Winter Storm Warning from 4am Sunday to 4pm PST Monday for Cascades in Lane County.
WA...Winter Storm Warning until 10am PST Monday for South Washington Cascades.
PZ...Small Craft Advisory from 3pm to 10pm PST Sunday for Columbia River Bar.
Small Craft Advisory until 10am PST Monday for coastal waters from Cape Shoalwater WA to Florence OR out 10 nm.
Small Craft Advisory until 7pm PST Sunday for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 nm.
Hazardous Seas Watch from Sunday evening through Monday afternoon for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 nm.