Cape Lookout to Florence OR between 150 and 250 NM Offshore Forecast
|Tonight...S Winds 20 To 30 Kt. Seas 7 To 11 Ft. Areas Of Fog With Vsby 1 Nm Or Less.|
|Sat...S Winds 20 To 30 Kt, Increasing To 25 To 35 Kt. Seas 7 To 13 Ft. Areas Of Fog With Vsby 1 Nm Or Less. Rain With Vsby 1 Nm Or Less.|
|Sat Night...W Winds 20 To 30 Kt, Diminishing To 15 To 20 Kt. Seas 10 To 12 Ft.|
|Sun...S To Sw Winds 15 To 25 Kt. Seas 10 To 13 Ft.|
|Sun Night...S Winds 20 To 30 Kt. Seas 9 To 16 Ft.|
|Mon...S Winds 20 To 30 Kt. Seas 12 To 20 Ft.|
|Mon Night...S To Sw Winds 15 To 25 Kt. Seas 16 To 20 Ft.|
|Tue...W To Sw Winds 10 To 20 Kt. Seas 13 To 16 Ft.|
|Tue Night...W To Nw Winds 5 To 15 Kt. Seas 11 To 13 Ft.|
|Wed...N To Nw Winds 5 To 15 Kt, Becoming N. Seas 9 To 11 Ft.|
|Wed Night...Variable Winds Less Than 10 Kt, Becoming W To Sw 10 To 20 Kt. Seas 8 To 10 Ft.|
| Area Forecast Discussion|
...Updated National Weather Service Portland OR
933pm PST Fri Dec 4 2020
Updated Aviation and Marine Discussion
High pressure expected to maintain mild weather through Saturday morning. Columbia Gorge gap flow will bring another round of
breezy to windy conditions to the western Gorge and portions of the Portland Metro area through Saturday. A weakening front will move across the area on Saturday bringing precipitation Saturday evening through Sunday. Drier conditions later Sunday and Monday before the next upper low crosses Tuesday/early Wednesday and another Thursday/Friday.
Tonight through Monday night...High Pressure is well established and the low clouds and fog in the south valley was rather stubborn to leave today. It is in fact still hanging on east and south of Eugene centered in the Middle Fork Willamette River drainage. There is also a little bit of low cloud hanging on over the far eastern edges of our Central Columbia River Gorge Zone. Will give until about 7pm tonight before the low clouds and eventually fog return to those areas this evening. Elsewhere will likely remain relatively cloud free until Saturday when upper low pressure approaches the coast. Meanwhile, still looking at increasing gorge winds tonight as pressure gradients increase between the approaching surface reflection of the upper low and cold higher pressure air east of the Cascades. This event is somewhat weaker than the previous on Wednesday and still has enough to bring 40 mph gusts in Troutdale near the immediate mouth of the Gorge and 60-70 mph for the favored wind spots. Out of those favored windy areas, air stagnation will be the primary concern. Will leave the advisory in place as is. may need to tack on another dense fog advisory tonight as well if the stratus drops in elevation similar to last night. Also for tonight, a high energy west swell will continue sneaker wave conditions through this evening.
Unfortunately, the models are still in notable disagreement regarding what form the upper low pressure area will arrive in Saturday night and Sunday. The GFS brings an open trough with precipitation focus over the Cascades and Gorge while the EC and Canadian closes off a low and sends most of the precipitation to the south. In either case, easterly pressure gradients will remain in place which keeps cooler air dammed up again the east slopes of the Cascades, including the Central Gorge and Upper Hood River Valley. Otherwise, snow levels will remain fairly high as the preliminary southerly flow brings warmer air over the region. With that set-up, feel there is a credible threat of freezing rain for the Central Gorge and Upper Hood River Valley. The unfortunate part is just how much Quantitative Precipitation Forecast will occur over the colder and likely sub-freezing air for those two areas. The GFS solution could bring advisory level icing with just over 0.10" of accumulation possible while the closed low solutions bring a few hundredths at most. Have favored the closed low solution for now, but compromised with higher overall Probability of Precipitation and also have included a chance for freezing rain in the central Gorge and upper Hood River Valley. Will see if this afternoon's runs start showing increased unity for future decisions.
Precip hangs on for early Sunday but does taper off with time. Also, expect the surface low will significantly lower the cross Cascade pressure gradient and also swing some southerly surface winds down the Willamette valley tomorrow. There is still some question as to if there will be enough wind and/or low level mixing to scour out the stagnant air conditions. At this time, feel there will be enough low level mixing, however, do not feel like it's a sure thing.
High pressure builds again Sunday night and Monday following the departing upper low, in whatever form it takes. High pressure aloft will not be as strong but should be enough to hold an approaching shortwave at bay until late monday night. Surface high pressure east of the Cascades will still be enough to keep colder air and Columbia Basin stratus in place for areas along the Columbia River. In fact, also do not think the stagnant conditions will have improved enough and will continue the Air Stagnation Advisory for the central Gorge/upper Hood River areas as well through the weekend and heading into next week. /JBonk
There is potential for another period of hazardous beach conditions early next week when powerful seas may result in 25 to 30 feet breaking waves Monday afternoon. This high surf will create dangerous conditions along the beaches through Tuesday.
Tuesday through Friday...Not many changes in the forecast package. Bulk of the previous discussion follows. The aforementioned shortwave within the southwesterly jet aloft late Monday and Tuesday will increase precipitation chances especially across the northern portion of the area. Uncertainty in the forecast increases through the middle of next week. But the majority of guidance suggests lower probability of precipitation Wednesday. There is a possibility of a low pressure system impacting the area Thursday but still quite a spread between ensemble members. /DDH
Offshore flow pattern continues across the coastal waters, with east to southeast winds gusting 20 to 25 kt. Even a few stronger gusts downwind of gaps in the coastal terrain. Not much chance in this pattern overnight. But, winds will turn more southerly on Sat as weak front approaches. The 12Z model guidance indicates 20-25 kt boundary layer wind speeds over the outer waters early Sat morning. Models then show speeds 25-30 kt 15Z Sat through early Sat evening. Strongest speeds look to occur beyond 10nm. However, as the front moves closer to shore, feel confident that gusts to at least 25 kt will occur inside 10 nm. Therefore, opted to add a small craft advisory PZZ250 and PZZ255. There is the possibility of 35 kt gusts beyond 10 nm between 17Z and 00Z Sun.
Weak high pressure settles over the waters Sunday and should hold through at least Tue. This will result in general wind speeds 15 kt or less. The 12Z operational GFS and ECMWF (European Centre for Medium-Range Weather Forecasts) offer differing solutions beginning Tuesday night. The GFS drags another front through the waters Tuesday while the ECMWF holds off until late Tue or even Tuesday evening. Much larger model differences late next week and this has major implications on the forecast wave heights. The GFS brings a fairly deep low pressure into the NE Pac Thu. The ECMWF is much more north with the low. Have trended toward the latter solution for now.
Wave heigheights 6 to 8 feet through Sat afternoon. Seas exceed 10 ft Sat evening with the frontal passage. A much larger swell train is expected to move into the waters Mon. The fetch for this expected swell is moving just south of the farthest Aleutian Islands near 41N 169W this afternoon. The low will approach the Pacific NW following closely along the Great Circle route through Sunday before shifting NE towards mainland Alaska. The models have come into better agreement on this swell, resulting in greater confidence that seas will get close to 20 ft. The GEFS wave probabilistic guidance indicates a 60 to 70 percent chance of seas 18 ft or greater late Monday and Monday evening. Swell periods close to 20 seconds will produce large-energy waves as they reach the surf zone.
Seas gradually ease Tuesday and Wed, but will remain above 10 feet. The 12Z ENP guidance, which is GFS-based, indicates another round of 20 ft seas Thu. However, the ECMWF wave guidance valid Thu shows 12-15 ft. The GEFS wave probabilistic guidance for Thu only gives a 10 to 15 percent chance of seas exceeding 18 ft. Weishaar
.PQR WATCHES/WARNINGS/ADVISORIES... OR...Air Stagnation Advisory until 7pm PST Tuesday for Central Columbia River Gorge-Upper Hood River Valley.
Air Stagnation Advisory until 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...Air Stagnation Advisory until 7pm PST Tuesday for Central Columbia River Gorge.
Air Stagnation Advisory until 10am PST Saturday for Greater Vancouver Area-I-5 Corridor in Cowlitz County-South Washington Cascade Foothills-Willapa Hills.
PZ...Small Craft Advisory on all waters tonight through Sunday evening.