Why is it so windy?
Wind is air rushing from high pressure toward low pressure. The bigger the pressure difference over a short distance, the harder it blows. Mountains, canyons and the afternoon sun can make it stronger still.
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High to low
Air piles up in some places (high pressure) and thins out in others (low pressure). It flows from the crowded side to the thin side, like water running downhill. Weather maps draw lines of equal pressure called isobars: where they're packed close together, the pressure drops fast over a short distance and the wind is strong. On a map with lines spread far apart, it's calm.
Earth's spin bends that flow, so instead of blowing straight from high to low, wind curls around them: clockwise out of a high and counterclockwise into a low in the Northern Hemisphere.
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Why it's windier in the afternoon
A few thousand feet up, wind is almost always faster than at the ground, where trees, buildings and hills slow it down. Overnight, the ground cools and the lowest air goes still, cut off from the faster air above. Once the sun heats the ground, warm air rises and cooler air sinks, mixing those faster winds down to you. That's why many places are calm at dawn and gusty by mid-afternoon.
Places that are always windy
- Gaps and passes squeeze air through a narrow opening and speed it up, like water through a nozzle.
- Coasts get sea breezes most afternoons: land heats faster than water, the air over land rises, and cooler ocean air rushes in underneath.
- Slopes get downslope winds when cold or heavy air pours off high ground. Santa Ana and Diablo winds are famous examples.
Questions people ask
- What makes wind gusty?
- Gusts are pockets of faster air from higher up that get mixed down to the ground, plus turbulence as wind tumbles over buildings, trees and hills. Sunny afternoons and passing storms make them stronger.
- Why is it windy before a storm?
- Storms are low-pressure systems. As one approaches, the pressure difference between it and the surrounding air grows, and the wind picks up to fill it in. Thunderstorms also push out gusty outflow winds ahead of the rain.