Several aspects of meteorology change with the seasons.

While we bid farewell to humidity in the winter, just as we do to snow and frost in the summer, we’re highlighting a meteorological phenomenon that sticks with us, regardless of the weather - settled or unsettled.

That phenomenon is wind- the cause for bitter chill in the winter, and a destructive part of hurricanes and thunderstorms in the warmer months.

Wind is a very simple concept on the surface. For those outdoors, it’s just the feeling of air moving in a certain direction. However, wind is driven by differences in pressure and Earth’s rotation, ranging from thousands of miles to just a few feet in scale.

On a synoptic scale, or distances of thousands of miles, air is driven by the pressure gradient force (PGF). High and low pressure systems across the Earth can change the pressure of two different locations many miles away. These surfaces disturb the air out of equilibrium, essentially changing the density of the air. The PGF drives air from high pressure to low pressure- evacuating air from a dense area and filling in the gaps to make the air’s density equal again.

The pressure gradient force becomes stronger as the change in pressure over a fixed distance becomes greater. For example, a weak high-pressure and a weak low-pressure system a thousand miles away will generate weak winds going towards low pressure, though two strong pressure systems over the same distance will generate a greater amount of wind, thanks to this imbalance.

This is the fundamental reason air diverges, or escapes on all sides, from high pressure, and converges, or comes together on all sides, to low pressure. Converging air allows air to rise, the basis for active weather to develop in low-pressure systems. The opposite is true in a high-pressure system.

The pressure gradient force does not account for Earth’s movements, however. Earth rotates about its axis, and its spherical shape means locations closer to the poles move at a slower speed relative to the rotation compared to places near the equator. The Coriolis Force explains this disparity. Due to this effect, all objects that would otherwise move in a straight line are actually deflected to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere.

To understand this effect better, imagine you are at the center of a spinning merry-go-round with a ball in your hand, and are asked to roll the ball to the edge. Your speed at the center of the equipment is much less than it would be at the sides. When you let go of the ball, the trajectory from your point of view looks to be straight, though your friend would see the ball curving to adapt to the increasing horizontal speed of the merry-go-round. This curving of the ball is the Coriolis force in action.

On a map, winds around a high and a low pressure system would begin to rotate, rather than PGF’s effect of bringing the wind straight in or out. In our hemisphere, winds converge counterclockwise around a low-pressure system, and diverge clockwise around high pressure.

While PGF and Coriolis are benchmarks to use on a large scale, these two forces alone cannot describe how we get wind in smaller phenomena, such as hurricanes and tornadoes.

Just like Coriolis forces, centrifugal forces are an apparent force that shapes weather systems. This force has major impacts on small-scale systems, such as tornadoes and hurricanes (to a lesser extent). Imagine you are exiting a car from a highway, and turn the car sharply to the right before you approach an intersection. While you are turning, your body will naturally lean to the left, almost as if it wants to keep going straight. This “outward push” is the centrifugal force in action, and opposes another inward force called the centripetal force. As this motion balances with the inward Pressure Gradient Force and the deflecting Coriolis Force, air will naturally rotate around a tornado or a hurricane. 

Wind is something nearly everyone has experienced, whether it’s a cool breeze on a warm day or strong gusts ahead of a storm. While it may feel unpredictable, wind follows clear physical rules that help keep Earth’s atmosphere in balance. These same forces shape daily weather, influence how cold or warm we feel outdoors, and drive some of the most powerful storms on the planet. By understanding why wind moves the way it does, we gain a better appreciation for the science behind weather forecasts and the invisible forces that affect us every day.