Cascade Head to Florence OR from 10 to 60 NM Marine Forecast
|Tonight...Ne Wind To 10 Kt With Gusts To 15 Kt. Wind Waves Ne 2 Ft At 4 Seconds. W Swell 12 Ft At 14 Seconds.|
|Tue...Ne Wind 10 To 15 Kt With Gusts To 20 Kt, Rising To 15 To 20 Kt With Gusts To 25 Kt In The Afternoon. Wind Waves Ne 4 Ft At 5 Seconds. Nw Swell 9 Ft At 13 Seconds.|
|Tue Night...Ne Wind 10 To 15 Kt With Gusts To 20 Kt. Wind Waves Ne 3 Ft At 5 Seconds. Nw Swell 6 Ft At 13 Seconds.|
|Wed...Se Wind 10 To 15 Kt. Wind Waves Se 3 Ft At 4 Seconds. W Swell 5 Ft At 13 Seconds. Secondary Swell W 5 Ft At 22 Seconds.|
|Wed Night...Se Wind 10 To 15 Kt, Easing To 5 To 10 Kt After Midnight. Wind Waves Se 2 Ft At 4 Seconds. Nw Swell 8 Ft At 19 Seconds. Secondary Swell W 6 Ft At 13 Seconds.|
|Thu...E Wind To 10 Kt. Wind Waves 2 Ft. W Swell 12 Ft.|
|Thu Night...Ne Wind To 10 Kt. Wind Waves 1 Ft. W Swell 11 Ft.|
|Fri...E Wind To 10 Kt. Wind Waves 2 Ft. W Swell 9 Ft.|
|Sat...S Wind 10 To 15 Kt. Wind Waves 2 Ft. W Swell 7 Ft.|
| Area Forecast Discussion|
National Weather Service Portland OR
318pm PST Monday Nov 30 2020
After decreasing showers today, high pressure will take hold and likely bring a prolonged period of east winds near the Gorge and dry weather are wide through the upcoming weekend. Away from the Gorge, light winds and persistent inversions will likely lead to stagnant air conditions with deteriorating air quality possible.
Tonight through Thursday...Region is now on the backside of the shortwave trough and associated cold front which moved across the region earlier. Trailing showers are becoming more and more sparse with each hour. Snow amounts in the Cascades have totaled 3-5 inches since last night with maybe an inch possible over the next several hours. Do not expect that snow in itself will present additional travel difficulties. However, for the most of the area (except the coast), clearing skies, cooling temperatures and residual water on roadways may lead to black ice tonight.
Looking forward, high pressure builds over the region but there are a couple issues. First, the 12Z model suite is in good agreement indicating offshore low-level flow developing late Tuesday, strengthening Tuesday night and peaking Wed. A general north to northeast low-level flow pattern develops Tuesday morning, but shifts to northeast to east by Tuesday evening. The 12Z NAM indicates a KTTD-KDLS gradient of -6 mb 00Z Wednesday and peaking at -10.2 mb Wednesday morning. Typically, the NAM has a tendency to end up 1 to 2 mb too weak with the max gradient. This trend is most prevalent with a deeper east flow layer, more in line with a synoptic downslope event vs. a pure gap flow event. Based on local rules of thumb, a -10 mb KTTD-KDLS gradient would produce max gusts to around 80 mph at Crown Point/Vista House.
The 12Z HREF mean wind gust guidance indicates 50-55 mph gusts early Tuesday evening in favored portions of Clark County, such as Camas and Washougal. The 4km WRF-GFS time-height section for Troutdale shows the main core of east wind extending to about 900 mb Tuesday night and then being compressed below 950 mb by Wednesday afternoon. Not anticipating the need for a high wind highlight for the west end of the Gorge as 75 mph or greater gusts will be very localized, primarily to areas near Crown Point/Vista House. However, a wind advisory may be needed for portions of the north Willamette Valley and east Vancouver metro on Wednesday. The east wind gradually decreases and becomes more confined to the western Gorge Wednesday afternoon through Thursday.
The second issue will be stagnant air developing away from the Gorge. Persistent inversions, low sun angle, and relatively light winds begin later Tuesday and seem likely to persist into the weekend. Have issued the advisory for our inland Oregon zones and will hold off on Washington citing partner preferences. The best possibility for breaking the stagnant conditions would be from a weak and dissipating front approaching the coast late Thursday.
Thursday night through Monday...There is some uncertainty in the extended as the aforementioned dying front has the ECMWF (European Centre for Medium-Range Weather Forecasts) chasing it with a largely dry cut off low forming and sliding across the region beginning Thursday night. It then meanders over the inland northwest through Monday. The remaining models simply bring the ridge back overhead with, maybe, another weak front Sunday.
Regardless, generally expect dry weather under cool conditions for the remainder of the week and weekend. areas of fog and/or frost will likely occur for most areas. Under a non-EC model solution, would also expect stagnant air to continue into early next week. /JBonk
Wind speeds over the waters continue to diminish early this afternoon. The 12Z NAM and GFS suggest wind speeds fall to 15 kt or less by late afternoon. The wind pattern becomes north to northeast overnight and then veer to east Tue. Offshore flow then persists through late in the week. The peak period will be Wed, with gusts to 25 kt likely over the north waters and gaps in the coastal terrain.
At 21Z seas were generally around 15 ft, although buoy 46248, Astoria Canyon, reported 17 ft. In general, model spectral guidance continues to be 2 to 3 ft higher than observed. Seas will remain above 10 ft through around 18Z Tuesday and have adjusted the Small Craft Advisory hazard to cover this. ENP and Gerling-Hanson plot for buoy 46029 show a 23-25 second extra-long period swell train beginning Tuesday morning. This eventually becomes the dominant swell by late Tuesday afternoon, with periods around 20 seconds. Thus, there will be a mix of 14 second west swell and a 20 second northwest swell. Wave heigheights look to fall below 10 ft Tuesday afternoon, but rise above 10 ft Wednesday evening, peaking in the low teens Wednesday morning. Weishaar
.PQR WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory from 10pm Tuesday to 10am PST Saturday for Cascade Foothills in Lane County-Central Coast Range of Western Oregon-Central Willamette Valley- Coast Range of Northwest Oregon-Greater Portland Metro Area-Lower Columbia-Northern Oregon Cascade Foothills- South Willamette Valley.
WA...None. PZ...Small Craft Advisory until 10am PST Tuesday for coastal waters from Cape Shoalwater WA to Florence OR out 60 NM.
Small Craft Advisory until 7pm PST Tuesday for Columbia River Bar.