Cape Lookout to Florence OR between 60 and 150 NM Offshore Forecast
|Tonight...W Winds 15 To 20 Kt. Seas 12 To 14 Ft. Chance Of Rain. Scattered Snow Showers.|
|Thu...W To Nw Winds 10 To 20 Kt. Seas 13 To 16 Ft. Scattered Snow Showers.|
|Thu Night...Nw Winds 15 To 20 Kt, Becoming W To Nw 10 To 15 Kt. Seas 10 To 16 Ft.|
|Fri...S Winds 20 To 30 Kt, Increasing To 25 To 35 Kt. Seas 9 To 14 Ft. Chance Of Rain.|
|Fri Night...S To Sw Winds 25 To 35 Kt. Seas 12 To 18 Ft.|
|Sat...S To Se Winds 25 To 35 Kt. Seas 14 To 19 Ft.|
|Sat Night...Se Winds 20 To 30 Kt. Seas 10 To 17 Ft.|
|Sun...E To Ne Winds 5 To 15 Kt. Seas 7 To 10 Ft.|
|Sun Night...Ne Winds 5 To 10 Kt, Becoming N. Seas 5 To 7 Ft.|
|Mon...N Winds Less Than 10 Kt. Seas 4 To 5 Ft.|
|Mon Night...N Winds Less Than 10 Kt, Becoming Nw. Seas 4 To 5 Ft.|
| Area Forecast Discussion|
National Weather Service Portland OR
445pm PST Wednesday Nov 30 2022
Low pressure will cross the region tonight and Thursday. This will bring an unstable air mass and plenty of showers. Showers will be mixed with snow down to the lowest elevations tonight and Thursday. Accumulations less than 1/2 inch will possible under the strongest showers, even close to sea level. Another upper low drops south and well off the coast Friday and Saturday, though most notable weather seems to stay along and just off the coast. The low moves inland across the OR/CA border Sunday with wrap around showers continuing through Monday. The action currently appears to relax a bit for the first part of next week.
.SHORT TERM...Tonight through Saturday: Another day of very tricky forecasting covering the next few days as details will most certainly matter. First recapping today, the cold front dropped south as previously expected to a point. It has stalled out mainly over southern Oregon but there is a small portion remaining over eastern Lane County. This area still is receiving numerous showers, bordering on stratiform rain and snow. Additionally, there were a few more break in the clouds this afternoon which heated temperatures a few degrees higher than forecast across the north. This happened to be enough to result in additional instability and a couple isolated thunderstorms. Meanwhile, snow did eventually transition to rain across the eastern Gorge and upper Hood River Valley this afternoon.
For tonight, the parent upper low center will drift to about 60 miles off the Washington coast then start to be absorbed into the main long wave trough. This will keep moderate west to southwest flow across the region with numerous showers funneling in to the Coast Range and Cascades. This should produce a fair amount of rain shadowing for the Willamette Valley tonight and early tomorrow, but can't fully rule out periodic showers bringing an rain/snow mix, or an all snow shower. Most accumulations should be less than a tenth or two, but some inland low elevation areas may pick up and inch of snow while many areas may receive nothing or a skiff. The main takeaway is don't be surprised to wake up to a small amount of snow Thursday morning. It won't take more then several hundred feet above the valley floors to have a better chance of accumulating a couple inches of snow, particularly near daybreak and through the morning hours.
In fact, have decided to add the north Oregon Coast and south Washington Coast zones above 500 feet into a Winter Weather Advisory through noon tomorrow. Those areas will have the added influence of relatively warmer ocean waters and a closer proximity to the trough axis and the added instability it affords. Like further inland, sea level locations may get no snow accumulations to upward of an inch, maybe more. Higher elevations along the immediate coast may behave more like the coast range with regard to snow accumulations, picking up more than a hand full of inches. Most of that should occur before daybreak, however. Otherwise, no changes to the current suite of advisories and warnings aside from extending the Oregon Cascades through 4am Thursday owing to the lingering bands from the stalled cold front and the slower transition to scattered showers tonight.
Thursday afternoon will see the upper trough axis push further inland, now slower in crossing the region and during the afternoon. This will give a slight bump to the instability, but is somewhat counteracted by the weakening upper trough. Still will see potential for thunderstorms, mainly along the Coast Range and westward mostly through tomorrow afternoon.
Thursday night and Friday will see those showers start to thin, but no completely go away. Current forecast has scattered type coverage continuing later Thursday night and most of Friday with primarily snow reaching the lower elevations and maybe a little bit of rain at the lowest valley locations. However, suspect this is overly aggressive and think the transitory short-wave ridge will have more of a dampening effect on the shower coverage than the NBM would indicate for that period. Would not be surprised to see the next forecast package take a dramatic shift to lower Probability of Precipitation late Thursday night and Friday morning during the commute hours.
Another fairly cold upper low will drop south along the B.C. coast bringing stratiform precipitation to the area as early as Friday late morning. The location of the upper low center is trending further offshore than previous days with the center now staying west of 130W. There is still a fair amount of uncertainly regarding the details of where a deformation band sets up and whether is along the coast and Coast Range, or if it remains just offshore. The blend and WPC guidance have trended it just offshore, but that still too close for comfort. it still warrants coastal areas keeping a close eye on the position of the band as even a 50 mile shift closer to shore could bring 1-2 inches of Quantitative Precipitation Forecast somewhere in those areas covering a short 6 to 12 hour window. Further inland may not see as much of an impact, but of concern will be the Gorge and central Gorge/Upper Hood River Valley in particular. The associated surface low will start drawing air from the Columbia Basin and could bring another round of cold air damming into the Gorge and Upper HR Valley. This time though, models suggest an all snow forecast would not necessarily be as much of a slam dunk with a few model ensemble members indicating warmer air possibly over running the cold pool(a region of relatively cold air) to bring a threat of primarily snow but also some freezing rain. As said before, details will most certainly matter in this case.
Otherwise, it appears most of the region will have a snow level at 1500-2000 feet and slowly climbing through the night into Saturday. Most of the precipitation will stay offshore, but some bands of rain and elevated snow could cross inland areas depending on the final track of the upper low. Again, some lower snow levels certainly remain possible surrounding the Columbia River and Metro area as potential colder air pushes through the Gorge into western Oregon. /JBonk
SATURDAY NIGHT THROUGH WEDNESDAY: Low pressure that brought low elevation snow will move out of the area tracking south along the coastline towards California Saturday night. Wrap around moisture into the northwest quadrant of the low will maintain showers across SW Oregon into Sunday which could track far enough north to bring measurable precipitation to Lane County overnight. Winds will turn offshore dragging cold Columbia Basin air west of the Cascades. Temps will drop into the upper 20s, low 30s across much of the area by Sunday morning with daytime highs reaching into the upper 30s, low 40s.
Shortwave ridging attempts to establish over the NE Pacific and into the Pacific NW between systems. However, there are so many undulations within the northwest flow aloft the low levels seem to be energized enough to produce weak showers, particularly over the high terrain through midweek. Some of the ensembles are ending up too cold within these showers and are producing accumulating snow for multiple sites in the Willamette Valley Monday and Tuesday but this is pretty unlikely. -BMuhlestein
Buoy observations at 3pm PST Wednesday showed west- northwest to northerly winds hovering between 10-25 kt, strongest over the southern waters. Although winds have decreased significantly, seas remain steep and hazardous with significant wave heigheights around 12-14 ft with a dominant wave period around 11 seconds. Seas should gradually improve on Thursday, but will likely remain at or slightly above 10 ft. Therefore, have extended the small craft advisories currently in effect through Thursday evening. Then, a very brief break from small craft winds and seas is expected Thursday night before the next frontal system impacts the coastal waters on Friday.
Models are in good agreement showing high-end gale force winds developing Friday morning before peaking Friday afternoon. In fact, the NAM generates 45-55 kt boundary layer wind speeds over the majority of the waters Friday afternoon. The GFS (Global Forecast System) is slightly weaker, but still has a core of 45-50 kt boundary layer speeds. The National Blend of Models (NBM) V4.1 indicates a 70 percent chance or greater probability of storm force gusts in the 24-hr period ending 10 pm Friday. This may be a little overdone based on raw ensemble guidance. The NBM v4.0 output for buoy 46050 shows about a 50 percent chance of storm force gusts. For now, have capped wind gusts just below storm force criteria of 49 kt. The NAM would also suggest a high probability of coastal jet development. It is a little early to pinpoint details. The surface low is expected to slide southward Friday night through Saturday, reaching a location near 41N 128W by 4 pm Saturday.
Model guidance has also shown an uptick for seas on Friday, now suggesting seas will peak around 18 ft. Given the strength of the winds with this system, this seems very reasonable. In fact, would not be surprised if seas end up peaking closer to 20 ft. -TK/Weishaar
NOAA Portland OR Office: Watches - Warnings - Advisories
OR...Winter Weather Advisory until noon PST Thursday for North Oregon Coast.
Winter Weather Advisory until 9am PST Thursday for Coast Range of Northwest Oregon.
Winter Weather Advisory until 5pm PST Thursday for Cascade Foothills in Lane County-Northern Oregon Cascade Foothills.
Winter Storm Warning until 4am PST Thursday for Cascades in Lane County-Northern Oregon Cascades.
WA...Winter Weather Advisory until noon PST Thursday for South Washington Coast.
Winter Weather Advisory until 9am PST Thursday for Willapa Hills.
Winter Weather Advisory until 5pm PST Thursday for South Washington Cascade Foothills.
PZ...Small Craft Advisory until 4pm PST Thursday for Coastal waters from Cape Shoalwater WA to Cape Falcon OR out 10 NM- Columbia River Bar.
Small Craft Advisory until 1am PST Friday for coastal waters from Cape Foulweather OR to Florence OR out 10 nm.Waters from Cape Falcon to Cape Foulweather OR from 10 to 60 NM.
Small Craft Advisory until 7pm PST Thursday for Waters from Cape Shoalwater WA to Cape Falcon OR from 10 to 60 NM.
Hazardous Seas Warning until 7pm PST this evening for Waters from Cape Foulweather to Florence OR from 10 to 60 NM.
Small Craft Advisory until 1am PST Friday for Waters from Cape Foulweather to Florence OR from 10 to 60 NM.