Ask the Meteorologist: Chetco Effect

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How come the Chetco River effects the weather in Brookings but the Rogue River has no affect on the weather in Gold Beach?

Curtis Kline, Medford

The Chetco Effect is just a phrase too account for the very warm easterly winds that can ever so quickly warm Brookings into the 70’s & 80’s. Although Brookings tends to see the warmest temperatures from this weather phenomena up and down the Oregon Coast, it is not the only location.

All of the Oregon coastal cities that lay just to the East of the Coastal Range Mountains tend to see very warm temperatures when winds are our of the East or Northeast. Even Crescent City sometimes can be as warm as Brookings.

So why is just east or northeasterly winds? Because when winds are traveling from east to west, these winds are downsloping the Coastal Range Mountains — meaning, the air parcels are riding over the mountain top and sliding down the windward side of the mountain. Anytime winds downslope a mountain, no matter what the direction may be, the air adiabatically warms (this just means the air compacts and warms without exchanging energy with surrounding air- just the air parcel itself warms).

There are few cities just to the east of the Coastal Range Mountains, so we really only see this happening for our Coastal cities which are located to the West. This is why it happens for an easterly wind.

The orientation of the Chetco River & the exact terrain of the Brookings Harbor is all the reason why this phenomena is so localized to the area. The simple answer to this question is the way the river is aligned with the Coastal Range Mountains. The river dumps out into the Pacific ocean from north to south (as opposed to east/west). In addition to that, the air traveling from the east hits the harbor and swirls around like a funnel because of the terrain. This helps to really warm the air up.

The same exact scenario occurs north of Brookings in Gold Beach with the Rogue River. However, the Rogue River dumps out into the Pacific from east to west (instead of north to south). The terrain is not as high & the terrain differences are the reason why it is not as enhanced here.

Meteorologist Alyssa Caroprese