Why is the Oregon and Washington coast foggy when it’s hot inland?

Why is the Oregon and Washington coast foggy when it’s hot inland?

Published on 10/12/22 at 05:14
By the staff of the Oregon Coast Beach Connection

(Newport, Oregon) – There’s a long-standing, even worn-out, witticism or saying among Oregonians: if it’s sunny inland, it means fog on the coast. While technically not entirely correct, certainly statistically, it happens often enough to be a frustration for Oregon Coast travelers in the summer. In winter and during other seasons, this is certainly not true. (Photo Oregon Coast Beach Connection: Hug Point near Cannon Beach in some fog)

Indeed, there is something. While the valley is sweltering in 100 degree heat, the Oregon Coast and Washington Coast can be foggy quite often. Certain weather mechanisms may be the cause, and they have been seen in action recently over the past couple of weeks as a fog bank clung to the Washington and Oregon coasts as inland regions experienced a record heat in October.

So why is it foggy on the Oregon Coast/Washington Coast when it’s nice inland?

It’s quite complex, but a lot depends on the temperature and pressure differences between inland and the coast. Essentially, hot air to the east rises, causing low pressure there. During this time, the ocean is much colder and this creates high pressure. High-pressure air likes to move through low-pressure regions, so the moist marine layer of the ocean is stripped from the upper layer of water. All that humidity stays low – basically low-flying clouds. It is therefore moved east towards the shore and beyond.

Other types of conditions must also be in play, but according to Brian P. Nieuwenhuis of the National Weather Service (NWS) office in Medford, “that’s the bottom line.”

As Nieuwenhuis told Oregon Coast Beach Connection:

“The hot air rises. So when the interior areas get very hot, the air above them, as a whole, begins to rise. It’s not doing it that quickly, given the large scale and other atmospheric processes, but it’s starting to increase. When air rises, it needs to be replaced, so air from other places is sucked in or “sucked in” from surrounding areas. This is what draws moist, cool sea air towards the coast. It is attracted, but because it is cold, moist air, it is blocked by the coastal mountains, and therefore mostly stuck on the coast.

That’s why if you’re coming from a very hot Tacoma and heading to Long Beach, or if you’re coming from Eugene and coming into Coos Bay, you’ll find it stuck.

Yet meteorologists observing the coast of Oregon or Washington State normally call these “sea surges” because it is the wind that stirs and pushes moist air towards the beaches.

“As the fog moves inland, the wind pushes it, as high pressure over the ocean to the northwest sends air towards the thermal trough (low pressure area due to rising temperatures). ‘hot air) inland,” Nieuwenhuis said.


A marine layer off Cannon Beach

After all, fog is just low clouds. It’s the same thing you see flying above you.

All of this is affected by elements far above. If there are a lot of high pressure systems moving over the ocean waters of the Washington coast and the Oregon coast, this pressure crushes the marine layer. The higher the pressure, the lower the fog stays. Then it tends to stay near the beaches and you get sunny conditions just inland.

Like what happened last week. The NWS continued to predict sunny conditions for the Washington and Oregon coast, but you continued to have fog right up against Cannon Beach, Bandon, and Ocean Park beaches. Drive a few blocks from the sand and you’ll have the warm sunny weather the NWS was talking about.

“How far inland it goes, and whether it can cross mountains, is due to other conditions in the atmosphere such as surface fronts, upper lows and highs, etc. .”, said Nieuwenhuis. “If the winds shift to the east, the fog will dissipate or be pushed out to sea.” (See also Manzanita Is Indeed the ‘Banana Belt’ of the North Oregon Coast – The Science Behind It)

These temperature differences between inland areas and coastal coasts are not as pronounced in early fall, as in September and early October. This creates conditions that make for the best weather of the entire year on the Oregon and Washington coast, referred to here as the second summer. This year, of course, it’s all a little off with 80-degree days still in mid-October.

Nieuwenhuis said most of the fog along these coasts is due to the marine layer.

Another fun fact about fog: “To technically qualify as fog, it must also obscure visibility to less than 5/8 of a mile (or less than 1 km),” Nieuwenhuis said.

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