Cape Shoalwater WA to Cape Lookout OR between 150 and 250 NM Offshore Forecast
|Today...W To Nw Winds 15 To 25 Kt. Seas 10 To 14 Ft. Rain.|
|Tonight...Nw Winds 20 To 30 Kt. Seas 12 To 17 Ft.|
|Mon...N To Nw Winds 20 To 30 Kt. Seas 13 To 17 Ft.|
|Mon Night...N Winds 20 To 25 Kt, Becoming Nw 10 To 20 Kt. Seas 10 To 13 Ft.|
|Tue...W To Nw Winds 10 To 20 Kt, Becoming Sw 20 To 30 Kt. Seas 8 To 11 Ft.|
|Tue Night...W To Sw Winds 25 To 35 Kt. Seas 9 To 14 Ft.|
|Wed...W To Nw Winds 20 To 30 Kt. Seas 13 To 16 Ft.|
|Wed Night...Nw Winds 10 To 20 Kt. Seas 12 To 16 Ft.|
|Thu...N Winds 15 To 25 Kt. Seas 11 To 16 Ft.|
|Thu Night...N Winds 10 To 20 Kt, Becoming N To Nw 5 To 15 Kt. Seas 9 To 15 Ft.|
| Area Forecast Discussion|
National Weather Service Portland OR
329am PST Sunday Nov 27 2022
The first of a series of winterlike systems is pushing across the area today, bringing widespread valley rainfall and heavy Cascade Snow. This will impact any post-holiday travel across the Cascades. Additional systems will drop down from the north to continue to bring rounds of valley rain and Cascade/Coast Range snow through the week. Chance for lowland snow for Thursday and Friday.
Short Term - Today through Wednesday
Southwestern WA and northwestern OR are currently in the warm sector ahead of an incoming cold front moving onshore early this morning. According to observations and radar imagery, the cold front is just north of Hoquiam, WA, and bringing brief heavy precipitation as well as gusty winds in the 25 to 40 mph range. With snow levels currently around 4500ft in the warm sector, low elevation rain and high Cascade snow will spread southeast across the area this morning. The snow levels will then quickly fall to around 2500 ft following the front. With precipitable water values 130-150 percent of average for this time of year, along with the synoptic and dynamic forcing moving into the area, the initial cold front will produce brief heavy snow along with strong gusty winds. A blend of 90th percentile NBM 4.0 and the NBM 4.1 matches current obs, and this blend has gusts of 35 to 55 mph at elevations above 1500 ft this morning. Behind the front, the precipitation will become more showery, but the instability will allow for higher snowfall rates through the afternoon. This evening, a jet streak on the backside of the trough will move into the area and reinvigorate precipitation production. HREF members show increasing probabilities of snowfall rates of at least 1"/hr to 50-90 percent, especially around midnight and after. There are even some areas of 30-50 percent chance of 2"/hr over the Lane County Cascades. Snow amounts in the Cascades from now until Monday afternoon are still easily in the foot to foot and a half range, along with blowing snow. Feel confident about the current Winter Storm Warnings in effect for the WA and OR Cascades today through Monday morning/afternoon. Another impact from tonigheights system will be even further instability to bring the chance of thunderstorms, mainly to the waters and coastal areas, then moving inland Monday.
Snow will decrease from north to south starting in the afternoon on Monday as the shortwave trough moves into the intermountain west, and a shortwave ridge moves in. Colder but drier air moving down in the northwest flow will result in a cold night Monday night, and clearing skies. Light snow showers will likely still be found in the high Cascades, but the surface pressure gradient turns offshore as very cold air surges south out of Canada and into the Columbia Basin. Offshore flow and the ridge aloft should result in less of a chance of precipitation to continue west of the Cascades, including the lowland valleys. Excluding the coasts, overnight temperatures will likely be below freezing Monday night as the skies clear, and some cold air seeps in through the Columbia River Gorge. NBM still shows a 20-40 percent chance of early Tuesday morning lowland snow, as there may be a few weak ripples in the northwesterly flow...but if it does occur, they wouldn't be much more than light flurries, so not expecting much of anything to accumulate on the ground. Overall, saw a decrease in the chance for lowland snow for early Tuesday morning.
The next system in the series moving down from the north will start approaching Tuesday. Southerly flow ahead of the system will once again surge snow levels up through the day and into Wednesday, reaching 3000-4000 by Wednesday late morning. However, with the cold air that may be entrenched within the Willamette Valley, especially near the Columbia River Gorge, precipitation type may be tricky with the next system during Tuesday. However, some of the models have slowed down with this system, so believe a lot of the precipitation chances are too overplayed on Tuesday. The better moisture won't arrive until Tuesday night and into Wednesday, when southerly winds will continue to increase and should scour out any remaining cold air, and result in snow levels around 1500 ft Tuesday afternoon then increasing to the 3000-4000ft level by Wednesday late morning. /Kriederman
/WEDNESDAY NIGHT THROUGH FRIDAY/...There remains high uncertainty in the long term forecast, but there are some overall trends. The low pressure system moving down over the area for Wednesday into Thursday has shown signs of slight warming but slightly wetter. 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 cold front will continue to drop southward across the waters this morning. Southwest winds ahead of the front will gust to around 20-30 kt, strongest across the northern zones. Winds quickly shift to the northwest behind the front and remain breezy, generally around 15-20 kt. Expect occasional gusts of 25-30 kt into Monday morning. Seas around 8 to 10 ft early this morning will build in response to a northwest swell arriving behind the front today. Expect seas to hover in the 12 to 14 ft range this afternoon through Monday. Have upgraded the outer waters to a Hazardous Seas Warning for tonight into Monday, while extending the Small Craft Advisory for the inner waters through Monday evening.
Weak high pressure shifts across the waters Monday night allowing northwest winds to ease to around 10 kt by Tuesday morning. But a developing low pressure system moving toward Vancouver Island Tuesday into Wednesday will result in increasing southerly winds. Most guidance suggests Gale force wind gusts of 30 to 40 kt are likely to develop across the waters by Tuesday night, along with the possibility of a coastal jet developing. Seas should climb back into the teens by Wednesday as well. Additional storm systems appear possible late in the week as the active weather pattern continues.
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. /Hartsock
NOAA Portland OR Office: Watches - Warnings - Advisories
OR...Winter Storm Warning until 10am PST Monday for Northern Oregon Cascades.
Winter Storm Warning until 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 this afternoon to 4pm PST Monday for Columbia River Bar.
Small Craft Advisory until midnight PST Monday night for coastal waters from Cape Shoalwater WA to Florence OR out 10 nm.
Small Craft Advisory until 7pm PST this evening for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 nm.
Hazardous Seas Warning from 7pm this evening to 2pm PST Monday for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 nm.