Florence OR to Point St. George between 60 and 150 NM Offshore Forecast
|Tonight...N Winds 15 To 20 Kt, Diminishing To 10 To 15 Kt. Seas 7 To 10 Ft.|
|Wed...Variable Winds Less Than 10 Kt, Becoming Sw. Seas 7 To 9 Ft.|
|Wed Night...S Winds 5 To 15 Kt. Seas 9 To 15 Ft.|
|Thu...W To Nw Winds 5 To 15 Kt, Becoming Nw 5 To 10 Kt. Seas 13 To 15 Ft.|
|Thu Night...N To Nw Winds Less Than 10 Kt. Seas 10 To 13 Ft.|
|Fri...N To Ne Winds 5 To 10 Kt, Becoming Variable. Seas 10 To 11 Ft.|
|Fri Night...Variable Winds Less Than 10 Kt, Becoming S 10 To 20 Kt. Seas 7 To 10 Ft.|
|Sat...S Winds 15 To 25 Kt. Seas 6 To 11 Ft.|
|Sat Night...W Winds 5 To 15 Kt, Becoming W To Nw 5 To 10 Kt. Seas 7 To 10 Ft.|
|Sun...Variable Winds Less Than 10 Kt. Seas 9 To 10 Ft.|
|Sun Night...S To Se Winds 5 To 15 Kt, Becoming S 10 To 20 Kt. Seas 9 To 12 Ft.|
| Area Forecast Discussion|
National Weather Service Medford OR
855pm PST Tuesday Dec 1 2020
An upper ridge axis is overhead with surface high pressure settling into eastern Oregon and low pressure along the coast. This is bringing a good west-east pressure gradient across the area this evening (BOK-LMT is around -9 mb). The 00Z KMFR sounding shows decent winds just off the surface around 850 mb and this is resulting in some fairly strong east winds over the upper slopes and ridges. Glancing at some of the higher RAWS that are prone to such winds (Slater Butte, Onion Mt, Parker Mt, and even Burnt Ridge) show wind gusts in the 25-40 mph range. Winds will stay mostly up above the highly populated areas tonight. But, since winds became aligned from the SE in the south end of the Rogue Valley this afternoon, it is still breezy in Ashland this evening with temperatures running in the low 50s!
Winds could stay up most of the night in Ashland. Models show the winds easing back toward morning as the gradient weakens, but this could affect the low temperatures there. We're still forecasting a low down in the low to mid 30s, banking on the winds decoupling, but if winds hold up all night, low temps may be in the 40s.
Meantime, satellite imagery is showing stratus in the Umpqua Valley with some fog already developing in the Rogue and Illinois Valleys. It is just a matter of time before this fills in overnight, so expect some low clouds/fog just about all west side valley locations (except Ashland) by morning. East side areas will be clear and cold with patchy fog, especially near lakes. Lows there will be mostly in the teens and 20s, but some single digits are possible in the Christmas Valley and Klamath Marsh NWR area. -Spilde
Updated 830pm PST Tuesday 01 Dec 2020...While are expected to remain high and steep across the area through this evening and in the outer waters south of the Umpqua River. A thermal trough will gradually weaken later this evening with north winds diminishing.
Long period west to northwest swell will arrive Wednesday morning with seas rising into Thursday afternoon. This will combine with incoming tide and a shorter period west-northwest swell at 13 seconds to bring a much increased chance of sneaker waves...with highest risk Wednesday but a continued risk into Thursday morning. Swell dominated seas are likely to become high with very long period on Wednesday night, continuing into Friday morning. This will bring increased hazardous bar crossings. There's some evidence suggesting a long period heavy swell could move into the waters by the start of next week. This is a new development, this we'll have to keep a close watch on how this pans out in the coming days. - Petrucelli/Sven
Updated Aviation Discussion.
01/12Z NAM/GFS in.
Areas of low clouds and fog persist over the west side valleys this afternoon, especially over the Umpqua Basin. Some locations there may not clear off today. Other than that, mostly clear skies prevail across the Medford CWA, even over the coastal waters.
A strong ridge remains off the west coast this morning, with dry northwest flow aloft over the Pacific Northwest. Strong inversions over the valleys will retard clearing during the daytime hours, and some valley locations may not clear at all in the afternoons and evenings.
The ridge will move slowly east and the axis will break to the east of the forecast area Wednesday and the flow aloft will become southwesterly. This will end the breezy easterly low level flow over the ridges, but the air mass will remain very dry and stable.
A short wave embedded in the southwesterly flow will approach the area Thursday, but it, and the associated surface front, will pretty much dissipate as it moves into the ridge. The ridge will rebuild thereafter, and easterly low level flow will return to the area. The dry and stable conditions will persist into the weekend.
This prolonged period of high pressure is creating conditions that will allow pollutants to accumulate. An air stagnation advisory remains in effect through Saturday morning for inland valleys. Please see the NPWMFR for details.
Extended discussion...Saturday morning 05 Dec through Tuesday night 08/09 Dec 2020...The story of the extended is changing as we'll start to see at least subtle differences in the weather pattern this weekend. It'll likely remain dry for most areas through the weekend, but the upper level pattern begins to shift Saturday night. An upper level trough will move into the area late Saturday into Sunday, and this one looks to hold up better than the Thursday trough. It will still weaken considerably as it moves into the strong ridge. However, models and their ensembles have been consistently indicating some light precipitation is possible along the coast, so have introduced slight chance Probability of Precipitation for Saturday evening and night. Away from the coast, dry conditions will likely continue, although, this trough may be enough to mix out some the stagnant air that will have accumulated in the valleys this week.
Models diverge in the evolution of this trough on Sunday. The GFS cuts it off into a closed low over eastern Oregon/northern Nevada while the EC is more progressive, moving the trough east of the area by Sunday night. Either way, this trough will flatten and weaken the strong ridge over the area, helping to allow the storm track to return to the region. Dry conditions are expected to continue into Tuesday morning, with valley fog and low clouds likely during the overnight and morning hours. Models indicate a front potentially moving into the area late Tuesday, however there are considerable differences in the timing and strength of this system. The key take away though is that it does not appear ridging will return and that the pattern will transition to a more active one mid to late next week. /BR-y
AVIATION...For the 02/00Z TAFs...Low clouds remain in place in the Umpqua Basin, including Roseburg with IFR ceilings and this is likely to continue through tomorrow morning despite weak to moderate offshore flow to a strong inversion. Visibility is also expected to decrease with patchy fog forming around 10z, but its possible it could happen be an hour or two earlier. Confidence remains low on on the timing of when conditions will improve, if at all Wednesday afternoon.
The Rogue Valley has cleared out, but the inversion remains in place which will limit the amount of mixing and thus drier air from aloft to mix down. The net result is for low clouds and areas of fog to form. Unlike last night, the lower conditions should develop later, but confidence on the timing in the TAF at Medford is medium, so watch for updates. Conditions will improve to VFR Wednesday afternoon.
Along the coast and just offshore, VFR conditions will continue through the TAF period due to a slightly stronger offshore flow. However, could not rule out IFR/LIFR ceilings at North Bend late tonight as weak southeast winds set up ushering in low level moisture.
East of the Cascades, including Klamath Falls, VFR conditions will continue through the TAF period. -Petrucelli
MARINE...Updated 100pm PST Tuesday 01 Dec 2020...While are expected to remain high and steep across the area through this evening and in the outer waters south of the Umpqua River. A thermal trough will gradually weaken later this evening with north winds diminishing.
In the meantime, the steep wind driven seas will be highest in the outer waters south of Cape Blanco, not quite building to hazardous seas conditions as winds peak early this evening.
A long period west to northwest swell will arrive Wednesday morning with seas rising into Thursday afternoon. This will combine with incoming tide and a shorter period west-northwest swell at 13 seconds to bring sneaker waves...with highest risk Wednesday but a continued risk into Thursday morning. Swell dominated seas are likely to become high and steep on Wednesday night, continuing into Friday morning. There's some evidence suggesting a long period heavy swell could move into the waters by the start of next week. This is a new development, this we'll have to keep a close watch on how this pans out in the coming days. -Petrucelli
.MFR WATCHES/WARNINGS/ADVISORIES... OR...Beach Hazards Statement from 4am PST Wednesday through Thursday morning for ORZ021-022. Air Stagnation Advisory until noon PST Saturday for ORZ023>026. Air Stagnation Advisory until noon PST Saturday for ORZ029>031.
Pacific Coastal Waters...Small Craft Advisory until 1am PST Wednesday for PZZ370-376.