Weather with Cliff Mass
10:51 am
Fri July 26, 2013

4 Reasons Why Seattle Has Best Summers in U.S.

The Seattle metro area recently topped the list of 50 most “chill cities” in the U.S., and KPLU weather commentator Cliff Mass says he’s not surprised.

“We do have the best weather in the whole United States by almost any measure,” he says.

There are several reasons for this excellent weather, says Mass, and we can thank the Pacific Ocean for all of them.

1. We rarely get too-hot temperatures

“The big picture, of course, is that our temperatures are mild because of the Pacific Ocean,” says Mass.

Our proximity to the cool ocean a guarantees us moderate temperatures, and shields us from frequent heat waves.

2. It’s 'virtually impossible' to be hot and humid 

“The fascinating thing is we cannot be really hot and really humid at the same time. It’s virtually impossible,” says Mass.

For us to be toasty, says Mass, the hot air would have to sweep in from the east (because to the west is the ocean, our natural cooler).

That inland air tends to be dry, and as it sinks down into the lowlands, “it’s compressed and warmed. And during that, the humidity tends to drop,” says Mass.

“So for us to be really warm, we have to have offshore flow, and that cannot bring high humidity,” Mass says. “The water’s cool, and cool water does not allow the air to pick up too much moisture. So (we have) moderate temperatures, and low humidity.”

3. We have a hard time staying hot for long

“We have what one would call is a version of natural air conditioning,” says Mass.

When we start heating up in Western Washington, the air gets less dense (because warmer = less dense), which causes the pressure to fall.

But the opposite is true offshore.

“Offshore, we have this east-Pacific high (pressure) that’s there all the time,” says Mass.

As the temperature rises inland, the two opposing pressures clash until, lucky for us, “the difference in pressure becomes so large that the marine air surges in. We call that the onshore push,” says Mass.

And that push, he says, is like a natural antidote to long stretches of sweltering heat.

“So we have a very difficult time staying warm for too long, because as we get warmer and warmer, the pressure falls more, and eventually the marine air’s going to surge in. So we’ve got that kind of protection,” he says.

4. We have some protection from global warming

We’re not as susceptible to climate change as other parts of the country, says Mass.

“And the secret, again, is the ocean—because the Pacific Ocean is warming up very slowly,” he says. “So we will have some protection, at least for 20, 50 years, because the water will stay cool, and allow us to have that marine influence that will moderate the temperatures even as global warming.”