Cascade Head to Florence, OR out 10 NM Marine Forecast
|Tonight...Nw Wind To 5 Kt. Wind Waves Nw 1 Ft At 4 Seconds. W Swell 5 Ft At 10 Seconds.|
|Tue...Sw Wind 10 Kt, Becoming S 10 To 15 Kt Later In The Day. Wind Waves S 1 Ft At 4 Seconds. W Swell 5 Ft At 10 Seconds.|
|Tue Night...S Wind 15 To 20 Kt, Rising To 20 To 25 Kt With Gusts To 35 Kt After Midnight. Combined Seas 6 Ft In The Evening, Then Building To Near 10 Ft Late. Dominant Period Of 10 Seconds. Rain After Midnight.|
|Wed...S Wind 25 To 30 Kt, With Gusts To 40 Kt. Combined Seas 14 Ft With A Dominant Period Of 10 Seconds. Rain.|
|Wed Night...S Wind 20 To 25 Kt With Gusts To 35 Kt, Becoming Sw 15 To 20 Kt After Midnight. Combined Seas 12 Ft With A Dominant Period Of 13 Seconds. Showers. Slight Chance Of Tstms.|
|Thu...Sw Wind 15 To 20 Kt. Wind Waves 3 Ft. W Swell 16 Ft. Showers And A Slight Chance Of Tstms.|
|Fri...S Wind 10 To 15 Kt. Wind Waves 2 Ft. W Swell 14 Ft.|
|Sat...S Wind 10 To 15 Kt. Wind Waves 2 Ft. W Swell 9 Ft.|
| Area Forecast Discussion|
National Weather Service Portland OR
814pm PDT Monday September 21 2020
Updated Aviation Discussion
Expect fairly seasonable and mainly dry weather through Tuesday before a more active storm track brings a period of wet weather beginning Wednesday and continuing through at least the end of the work week.
Tonight through Thursday...Water vapor satellite imagery shows a weak upper shortwave near 130W moving towards the OR/CA coast. A weak surface trough along the OR/wA coast will push inland this evening as heigheights build over the waters tonight. There is a slight chance this may provide a few areas with light rain along the northern OR/southwest WA coast and northern parts of the Willamette Valley and Cascade foothills through tonight. Most likely will only see midlevel clouds associated with the upper wave. Expect clouds to continue to increase Tuesday limiting sunshine as temperatures likely will only reach the mid 60s to low 70s.
The first fall weather system for our region this year is expected Wednesday. A strong upper low can be seen in water vapor satellite imagery developing in the southern Gulf of Alaska. Models are in good agreement a strong front will drop southeastward across the area Wednesday bringing gusty winds and heavy rain at times. Recent model runs have slowed the arrival of the frontal system. Rain will likely begin along the north coast late Tuesday with the heaviest rain there expected Wednesday morning into early afternoon. Rain will likely push into the Portland Metro area by Wednesday morning with the higher rainfall rates occurring late Wednesday afternoon through the evening. The rain will continue to move southeast reaching Lane county by Wednesday night. Rainfall amounts will vary across the area with the highest amounts expected across the higher terrain of the Coast Range and parts of the Cascades. Ensemble products are also increasing confidence in a heavy rain event to occur mid-week. NAEFS IVT values around 750 kg/ms coinciding with max precipitable water values around 1.0 to 1.5 inches between 00- 06Z indicate high probability of an atmospheric river with strong upper level synoptic support as well. The front accompanying the atmospheric river will weaken as it shifts southeastward across the area and will be rather transient, so no major hydrology issues are anticipated. Guidance suggests 1-2" of rainfall likely along the coast with the coastal mountains up to 3" or possibly 4" in spots. Valley locations should see at least 0.5 to 1", with some locations up to 1.5".
Along with the front gusty southerly to southwesterly winds will develop ahead of the front Tuesday night into Wednesday morning. Very breezy conditions are expected along the coast with the strongest winds expected Wednesday morning with gusts of 25 to 45 mph expected. While surface pressure gradients are not too impressive, models indicate low level winds around 925mb could mix down with some locations along the coast receiving wind gusts of 45 to 55 mph Wednesday morning through Wednesday afternoon. Behind the front cold air aloft will allow for more convective showers to develop and continued wet conditions. A broad upper level shortwave trough will move towards the Pacific Northwest Wednesday night into Thursday morning. Some deeper instability could result in a few thunderstorms across the waters and along the northern coast during this time.
Thursday night through Monday...The upper level jet will begin to lift Friday morning as broad upper ridge builds over the Pacific Northwest. A reinforcing shortwave trough will likely result in another round of more widespread showers Friday. Models suggest a compact surface low will move east toward the Oregon coast Friday with more rain and showers expected. Shortwave ridging gradually shifts eastward across the Pacific Northwest over the weekend. This will result in showers decreasing Friday night into Saturday across the area. Sunday looks more to be mostly dry with high temperatures climbing back into the 70s. High pressure will continue to build Monday as temperatures continue to warm. /DDH
Surface pressure gradients not too strong, and with high pressure over the coastal waters, will see winds 10 kt or less tonight into Tue. Seas generally stay at 4 to 6 ft.
Broad area of low pressure over the Gulf of Alaska this week. This will send a series of fronts across the coastal waters and into the Pac NW. First up arrives later Tuesday night and Wed. Winds gradually pick up over the waters Tuesday afternoon, with strongest winds not arriving until later Tuesday night or Wednesday morning. Good bet will see gusts 30 to 40 kt on the waters at that time. But, would like to wait a tad longer before pulling string on Gale Warning. So, for now, will have Small Craft Advisory on the waters for Tue afternoon and evening, starting on the outer waters first. Then, maintain Gale Watch later Tuesday night and Wed, again, starting on the outer waters first. Seas build gradually as the wind picks up, with seas to 10 ft later Tuesday night, and around 15 ft on Wed.
Winds ease back behind the front Wednesday night, but will maintain breezy conditions at times through Thu. Another front will arrive on Fri, with another round of breezy southerly winds and higher seas. A large westerly swell looks to then move across the waters later this week, which will keep seas in the mid teens and bring a high threat for sneaker waters. /Rockey
.PQR WATCHES/WARNINGS/ADVISORIES... OR...None. WA...None. PZ...Gale Watch from Tuesday evening through Wednesday evening for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 NM.
Small Craft Advisory from 2pm to 11pm PDT Tuesday for coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 NM.
Gale Watch from late Tuesday night through Wednesday evening for coastal waters from Cape Shoalwater WA to Florence OR out 10 NM.
Small Craft Advisory from 8pm Tuesday to 5am PDT Wednesday for coastal waters from Cape Shoalwater WA to Florence OR out 10 NM.