Predicting Wind and Weather: Forecast from Wind Direction

Where does the wind come from?

Wind is a mass of air that moves because of differences in temperature and atmospheric pressure.

Wind can be a nuisance (remember that walk on the beach with your hair in your face) or even dangerous in a storm. Yet it plays an essential role in nature: oxygenating the oceans, spreading minerals, helping some plants reproduce and more. But where does it come from?

Solar radiation is not uniform across the planet, so it creates air masses at different temperatures. Warm air, which is lighter, rises and forms a zone of low pressure (a depression). Cold air, which is denser, sinks and creates a zone of high pressure (an anticyclone). Air then moves from high pressure to low pressure: this stream of air is the wind. Its role is to even out the pressure difference, and the bigger the difference, the stronger the wind.

But wind does not travel in a straight line. The Coriolis force, linked to the rotation of the Earth, deflects its path and makes it spiral. In the northern hemisphere, air leaves an anticyclone turning clockwise, while air drawn into a depression swirls anticlockwise. On its way, air can pick up heat and moisture, and as depressions draw it in, they develop clouds and rain. Wind is therefore a key cog in the balance of our atmosphere.

To find out how clouds turn into rain, read why it rains.

The role of wind in weather forecasts

Combining pressure (barometer) with wind (strength and direction) lets you anticipate the weather more accurately.

To predict the sky over the next few hours, the first reflex is to watch the atmospheric pressure: it shows whether an anticyclone or a depression is arriving, and so whether the weather will stay fine or turn bad. A barometer, the instrument that measures this pressure, is the perfect tool for reading the day's trend without checking the forecast. For even finer predictions, combine its readings with the wind.

Two instruments measure the wind: the anemometer, which gives its speed (compare it with the Beaufort scale, which runs from 0 to 12: the higher the number, the stronger the wind), and the weather vane, which shows its direction.

What does wind direction tell you?

Wind direction affects humidity and temperature, and gives valuable clues about the weather to come.

Each direction has its meaning. In summer, a northerly or easterly wind usually means a clear, hot and dry sky; in winter, dry but cold weather. A southerly wind in summer brings heat and humidity, a combination that favours thunderstorms. A westerly wind blows a fresh breeze, pleasant in summer but often bringing rain, in winter as well.

And keep an eye on your weather vane: with a south-westerly wind in winter, make sure everything is secured, because a storm may be brewing. These are rules of thumb, not guarantees. Forecasting the weather accurately means watching several things at once: pressure, humidity, temperature and wind. Now you know what to do to become a true weather master.

Keep exploring: predicting the weather with a barometer.