Cape Shoalwater WA to Cape Lookout OR between 150 and 250 NM Offshore Forecast
|Today...N Winds 10 To 20 Kt. Seas 5 To 7 Ft.|
|Tonight...N Winds 10 To 20 Kt, Becoming N To Nw 5 To 15 Kt. Seas 5 To 7 Ft.|
|Sat...W To Nw Winds 5 To 10 Kt, Becoming S To Sw 10 To 20 Kt. Seas 6 To 8 Ft.|
|Sat Night...S To Sw Winds 10 To 20 Kt. Seas 6 To 8 Ft.|
|Sun...W To Sw Winds 10 To 20 Kt, Becoming S To Sw 20 To 30 Kt. Seas 7 To 8 Ft.|
|Sun Night...Sw Winds 20 To 30 Kt. Seas 7 To 12 Ft, Building To 10 To 18 Ft.|
|Mon...Sw Winds 25 To 30 Kt. Seas 13 To 22 Ft.|
|Mon Night...W To Nw Winds 20 To 30 Kt. Seas 17 To 20 Ft.|
|Tue...W To Nw Winds 15 To 25 Kt. Seas 13 To 18 Ft.|
|Tue Night...W To Sw Winds 20 To 30 Kt. Seas 10 To 14 Ft.|
| Area Forecast Discussion|
National Weather Service Portland OR
326pm PST Wednesday Dec 1 2021
A weak cold front will push across region tonight into early Thu, bringing cooler temperatures and foggy conditions on either side of it. Mostly dry to close the week with valley frost possible, especially Friday morning. Rain and some high Cascade snow then returns Saturday with temperatures more typical of early December. A stronger system will cross somewhere into the Pac NW or British Columbia with moderate to heavy rain possible.
.SHORT TERM...Tonight through Saturday...Minimal significant weather concerns through the first half of the weekend. High clouds associated with a stalled weak front to our north prolonged the fog and low cloud burnoff for the northern half of the forecast area while the coast continued to see areas of fog/low stratus pushed onshore. The Tualatin Valley was the last inland area to see fog lift and low clouds may not completely clear for more than an hour or two this afternoon/evening before settling back in place for the night.
The weak front will slide south tonight and weaken further with light rain possible from roughly Salem northward. Elsewhere and on either side of the rain, fog and low clouds will return with the south Valley and coast being the most likely to fog in. Development will happen shortly after sunset this evening. Some improvement will occur when the frontal remnants pass by, but then conditions likely deteriorate later overnight.
Thursday night and Friday will be clearer and cooler. As temperatures return closer to their 1990-2010 normals, valley temperatures will fall toward the mid and lower 30s which will bring a fair threat for frost.
Another, and slightly more coherent, cold front crosses late friday night and Saturday. It may hold together enough to bring a couple inches of snow, mainly to the North Oregon Cascades northward.
Temperatures will still be cooler than the last several days, but for context, back toward normal.
It appears there will be enough mixing over the following few days to justify letting the Air Stagnation Advisory expire as planned Thursday. /JBonk
Saturday Night through Wednesday...High pressure will quickly build behind Saturday's front with temperatures returning above normal under dry weather. Sunday night will also be mild as warm advection dominated from the building ridge. There is then general agreement among the medium range models that some form of upper trough (maybe a closed low) will form over the Gulf of Alaska Sunday night and then dive southeast toward the Pac NW on Monday. There are widely varying model solutions to this feature and whether it sends the primary energy and precipitation over us, or perhaps as an unwelcome addition to the B.C. coast. This one bears watching for us as wherever the precipitation makes landfall, it will bring 1.50-2.00 inches of rain over a fairly short 12 hour period. Main concern for us would be rain rates over some of our recently burned areas. At this time, it doesn't appear they would be excessively high per hour, but it is also very difficult to ascertain hourly rain rates over the coarse mid-range model output. Models also vary widely on how cold this system will be and especially with regard to potential Cascade snow accumulations.
High pressure remains offshore through this event and does nudge ridging briefly over the Pac NW for Tuesday . Even then, another weak shortwave passes through the ridge's flow for additional precipitation threats Tuesday and Wednesday along with near normal temperatures. /JBonk
500 mb heigheights should gradually rise this weekend as a ridge over the western United States becomes more amplified as suggested by the EURO and GFS ensemble means, potentially rising above 580 dm by late Sunday. The WPC's cluster analysis is also showing a strong signal for ridging over the region this weekend. This should result in slightly warmer and drier than normal conditions. That said, the deterministic EURO/GFS are both showing a weak closed surface low moving into the forecast area on Saturday, bringing a chance of rain for locations north of Eugene. The exact strength and track of this low remains quite uncertain, and Saturday could wind up mainly dry if the low tracks far enough to the north. The EMC's GEFS plumes for Quantitative Precipitation Forecast at Astoria, Portland, and Salem show many ensemble members that produce no Quantitative Precipitation Forecast at all on Saturday. In fact, there are considerably more ensemble members producing no Quantitative Precipitation Forecast at all than members that do produce light Quantitative Precipitation Forecast amounts. Therefore, current messaging for Saturday is only a slight chance of rain, which is also what the NBM suggests. Chances for rain are highest over southwest Washington and the far north OR coast. /JBonk
High pressure over the waters will slowly erode tonight as a weak cold front pushes inland from the north Pacific. While this front will make landfall early Thursday morning, the only real impact to the marine waters will be an increase in wind speed and a change in direction. Winds will become northerly tonight into Thursday and increase to around 15 to 20 kt with gusts around 25 kt. In the central Oregon waters, could see gusts up to 30 kt, but likely will stay slightly below those values. Seas should stay a consistent 9-12 ft at 14 seconds through at least Friday.
By early Saturday morning, winds will have slowly shifted to the south as a broad low pressure system moves over the waters. This system has quite a bit of uncertainty with it as there has been a lot of variability in model outputs. With that being the case there are several different outcomes that are possible. The outcome that appears to be the most likely are southwesterly winds around 10 to 15 kt with gusts around 20 kt, and seas around 6-9 ft at 13 seconds. This slightly more active pattern will persist through Sunday.
Much more active weather is expected on Monday but this system has a significant amount of variation in outputs and very high uncertainty. Some models are forecasting seas exceeding 17 ft, while others are keeping seas closer to 10 ft. Because of this drastic difference, have kept conditions more 'moderate'. -Muessle.
NOAA Portland OR Office: Watches - Warnings - Advisories
OR...Air Stagnation Advisory until noon PST Thursday for Cascade Foothills in Lane County-Cascades in Lane County-South Willamette Valley.
WA...None. PZ...Small Craft Advisory until 4am PST Friday for coastal waters from Cape Shoalwater WA to Florence OR out 60 nm.
Small Craft Advisory until 7am PST Thursday for Columbia River Bar.
Small Craft Advisory from 1pm to 6pm PST Thursday for Columbia River Bar.