How Cape Blanco is a Dividing Line in South Oregon Coast Weather

Published 02/17/22 at 11:02 PM PST
By Oregon Coast Beach Connection staff

(Port Orford, Oregon) – At 245 feet high, and on a big bump where Oregon itself juts outward, the south Oregon coast's Cape Blanco winds up almost the westernmost point in the lower 48 states – aside from a spot on the Washington coast. In the scenic and geographic sense, it's a special place.

Yet it also has an impact on the weather patterns of the southern Oregon coast, but not in ways you'd expect. Right about here is the pinnacle of where the state slowly stretches westward, starting roughly about Coos Bay and then dipping back again around Gold Beach. So, things are going to shift to some degree. Indeed, if you look at weather reports of the south coast, especially those offshore, winds tend to be forecast differently north of Cape Blanco and south of it. But the fact the state bulges outward here is just part of the story of that meteorological dividing line.

Weather is truly different north of here and south of here. But why?

At the Medford office of the National Weather Service (NWS), this is what they deal with all the time. There, meteorologists Dan Weygand and Brian Nieuwenhuis explained the complex mechanisms involved, but there's a surprising bigger factor: the coast range south of Cape Blanco is simply higher. This changes things.

“There isn't as much of a variation in height of the terrain north of Cape Blanco,” Weygand said. “The peaks are higher when you get into Curry County.”

This cuts off the influence of east winds to some degree, and that can have various effects, depending on the kind of weather pattern this part of Oregon has.

When it comes to many runs of awesome weather on the south coast, it can be a thermal trough parked offshore – an area of cooler temps and lesser pressure – while there could be an area of higher pressure inland creating the heat. This kind of system creates winds from the north, while a cold front (or storm) will create winds coming from the south.

In the case of the northerly winds and a winter heatwave, the area south of Cape Blanco sees something a little different than up at Bandon or Coos Bay.

“Because of the height of the coastal range south of Cape Blanco that pattern gets enhanced, whereas usually it's a lot weaker north of Cape Blanco,” Weygand said.

No surprise, this can be part of the famed Chetco Effect, Nieuwenhuis said, but it's more complex than that.

Nieuwenhuis likened the Oregon coast to a curb that runs along the street from north to south, where rainwater can't get over it but is instead deflected along it. So if winds are coming from the north or south, they get deflected along the shore.

Courtesy Bureau of Land Management

“Now we throw in Cape Blanco (or any cape, as this same process occurs with Cape Mendocino in CA),” Nieuwenhuis said. “The Cape is like a rock we place against the curb. The water slows a bit ahead of the rock, but flows even faster once it gets around it and downstream due to the built up of momentum / pressure. This same process is why winds downwind of Blanco tend to be faster.”

This bulge in Oregon and the cape – along with the higher coast range - are why weather patterns get forecast differently there, so often mentioning “north of Cape Blanco” or south of it.

Courtesy Oregon State Parks

The biggest influence is often east winds coming over the Coast Range and getting warmed up as they do. If there's enough push to the east winds during a warm spell, and southern Oregon has it hotter than up north (which is often the case in summer), then those east winds come over the higher southern coast range and get warmed up even more.

“So this east wind tends to create warmer conditions along the coast, where the marine layer is pushed a bit offshore,” Nieuwenhuis said. “This warming is the 'Chetco Effect' in the Brookings area, and while it makes for warm temperatures there, it can also further enhance the thermal trough pattern overall.”

Then just a little ways northward, that pattern can make a difference and spoil it for everyone else.

“In places where the cooler marine air pushes onshore instead (where the east winds are weak or absent), temperatures will cool,” Nieuwenhuis said. “In other words, the cooling and warming temperatures can vary quite a bit depending on the pattern and location. So, Brookings may be warmer with winds out of the east/northeast, but to the north at Bandon, winds are onshore and cooler as the marine layer pushes inland due to the lack of an east wind.”

On a micro scale, the region around Cape Blanco can really have some interesting effects, Weygand said. Port Orford, just to the south, can be quite protected from winds at times because the cape is there.

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