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Why San Francisco Gets So Windy and Foggy in the Summer | Bay Curious | The California Report | KQED News
"Every day Will Pearson bikes from his home in San Francisco's Marina district to his office in the Financial District. His morning ride along the Embarcadero is pleasant and calm, but he has noticed the wind picks up significantly on his ride home.

"I’ve always wondered why different parts of the day have such different levels of wind," said Pearson.

Fortunately, it's not too complicated, said meteorologist Jan Null.

Here's the simple explainer from KQED cartoonist Mark Fiore."


"For more detail, here's the breakdown.

Why it's windier in the afternoon

• Air always moves from areas of high pressure to areas of low pressure.
• Hot air rises and is less dense, and is typically low pressure, while cold air sinks and is dense, and is typically higher pressure.
• Over the course of the day, the air inland heats up in California. But air remains cool over the ocean — where the water stays about the same temperature all day.
• The cold, high-pressure air from over the ocean rushes inland, toward the warm, lower pressure air.
• It takes the path of least resistance, squeezing through sea-level gaps in the mountains and ridges — the biggest of which is at the Golden Gate.
• This creates something known as the Bernoulli Effect. "Think about a garden hose. You have the water cranked up all the way and you have the flow coming out of it. Well, you put your thumb over it, you restrict it down, and all of a sudden you shoot 20 yards across the driveway," said Null. "The same thing happens if you compress air down to a smaller gap like through the Golden Gate or the San Bruno Gap."

That's why the winds are strongest on the days where it's hottest inland and still cool on the coast, when the temperature and pressure difference is the biggest.

Why it's foggy in the summer

The temperature differences also explain why the Bay Area gets so much fog in the summer.

• There is a system of high pressure over the Pacific Ocean called the North Pacific High. In the summer, it gets stronger, creating big clockwise winds over the ocean.
• Those winds push the surface water of the ocean away from the California coastline.
• Very cold water from deep in the ocean rises to the surface. This is called upwelling.
• Something known as the California Current also brings cold water south from Alaska.
• When the sea breeze blows over this much colder water, condensation forms — creating fog.
• The fog comes inland in the summer for similar reasons as the wind: While it stays cool by the ocean, the high temperatures inland create lower pressure, and the fog is sucked in through gaps in the mountains, like the Golden Gate.

That's why we see picturesque summer fog rolling in past the Golden Gate Bridge in the afternoon.

"Nothing's going to move them out until the sun comes up the next morning and evaporates it," said Null.

Our topography also explains why one neighborhood can be foggy, like the Sunset, and another warm, like the area in Sausalito known as the Banana Belt. The hills and ridges direct the path of the fog and wind, creating these microclimates.

Will our fog and wind remain?

The amount of summer fog has decreased 33 percent over the last century, studies have found. Warming oceans and climate change could continue to affect the complicated weather systems that create our unique Bay Area fog and wind."
sanfrancisco  weather  fog  bayarea  2018  explainer  visualization  markfiore  jannull  meteorology  classideas 
3 days ago by robertogreco
The Seven Trends behind the Global Rise of Populism
But while ethnic nationalism as a system of belonging eroded, in many countries no alternative form of nationalism rose to replace it. It has long been acknowledged that a civic nationalism can arise, as an “open” nationalism defined by membership in a society, emphasizing a shared destiny rather than an imagined shared origin. But the weight of history has made many countries slow to attempt to build it as a serious alternative.

Worse, our clinging to an obsolete vision of nationalism is contributing to an identity crisis among minorities, who feel neither “of here” nor “of there”. There is a limit to how much someone can assimilate, even if they want to — but there’s the other question of whether it is humane or even desirable. Diversity is supposed to be a boon — but we are proceeding from an outdated concept of nationalism that sees it as a threat.

Identity — “who am I” — is among the deepest questions there is. In the absence of an effective system of belonging, individuals will not give up on identity — they’ll snap back to the most familiar identity they know, regardless of its usefulness or appropriateness. Hence the dizzying snap-back to outdated closed nationalisms in an age where our societies are more diverse than ever.

Tragically, the one country which had offered the greatest and most inspiring example of an open nationalism — the United States of America — ended up electing to office a team of ethnic nationalists. And this has been, in no small part, a result of a political failure.
world  politics  explainer 
14 days ago by corrales
HPE: Moral Code, The Ethics of AI
Video directed by Dress Code about the ethics of AI.
Great simple graphic and type animations.
type  text  video  film  animation  infographic  explainer  motion 
21 days ago by oliverdonovan
How the cloud works | CERT NZ
We’ve all heard people referring to ‘the cloud’ but it’s often not clear what that actually means. What is the cloud?
cloud  guide  explainer  computing 
4 weeks ago by bezthomas
A timeline of Earth's average temperature
Vertical, cartoonish timeline of the climate's average temperature
dataviz  timeline  vertical  unusual-viz  climate  comic  explainer 
8 weeks ago by stevecarufel

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