The wind brings us clear blue skies and storms, makes a sailboat sail and chills us to the bone. But have you ever wondered where it comes from? Here the Lifeboat gives you a beginner’s guide to wind and its extreme effects

The wind brings changeable and sometimes wild weather to the UK and RoI. By understanding a bit about wind, it can help us all predict the weather. And who can resist the chance to beat Michael Fish at his own game?

Wind is moving air. It’s created by differences in air pressure – that’s how hard the air is pressing on the surface of the earth. Air is a gas, so when it warms up, it becomes less dense, lighter and rises, and when cooled, it becomes more dense, heavier and sinks.

If a packet of air becomes warmer and rises, new air is sucked in behind it. That air must in turn be replaced. The replacement air will ultimately have sunk from higher levels, creating a cycle. Air is flowing across the surface of the earth from areas of higher pressure to areas of lower pressure.

We’ll feel the wind rushing faster the greater the difference between the focus of high and low pressure and the closer they are to each other. And the biggest differences in pressure will be found where temperature differences are the greatest – for example between the equator and higher or lower latitudes, and between land and sea. But air moves in all dimensions, not just in a simple up and down cycle, as there are many local and global factors at play.

On a small scale, the speed and direction of the wind is affected by natural features such as mountains and even by architecture. Most of us will have experienced the wind whipping down a street with high buildings either side.

On a large scale, in the northern hemishpere, winds spiral clockwise out from areas of high pressure and anticlockwise into areas of low pressure. These pressure systems can be localised or the size of a continent. Low pressure systems are usually associated with strong winds, cloudy skies and wet weather.

On a global scale, entire spiralling systems move too, affected by the prevailing wind and the rotation of the earth. Weather forecasters often talk about ‘a weak (or deep) low coming towards us from across the Atlantic’. Then you’ll experience the wind coming from different directions as each section of the spiral reaches you.

Wind swirls around you throughout the day. It’ll blow your whirligig around to dry your washing, it’ll keep you tacking in a yacht, it’ll lift a kite up high in the sky and make it twirl.

How wind helps us predict the weather
For centuries, people have watched, and to some extent predicted, the weather by the direction and speed of the wind:

• Weathervanes and weathercocks tell you which way the wind is blowing. The arrow/ beak points to the direction that the wind is coming from.

• Windsocks indicate the direction and force of the wind, with the smaller end pointing towards the direction the wind’s going to.

• Since 1805 sailors have used the Beaufort Scale to estimate wind speed from observing the wind’s effect on the sea.

• Anemometers make more precise measurements of wind speed and direction.

Since about 1860 meteorologists have been able to get one step ahead and forecast the speed and direction of wind before it reaches us by measuring air pressure with barometers – nowadays of great sensitivity.

But so many factors are at play at once that many different outcomes could develop from any snapshot of measurements. This is especially true at the north west tip of Europe, with such varied landscapes and with so many air currents from across the continents meeting within a relatively small area. The more stable the situation, such as a large strong high pressure system, the more certain the forecast. The more complex the situation, the more imprecise the forecast, despite the power of giant computers to process the probabilities.

High winds and high risk at sea
At sea, strong and prolonged winds create swell and waves. The wind can also add to or fight the effects of the tide. Predicted tide heights can appear inaccurate in very strong winds, and wind against tide can create rougher conditions.

Out at sea there’s no place to hide, no friction to slow down the wind, and no shelter.

In tropical storms or hurricanes, winds can reach up to 200mph, spiralling around a calm centre of low pressure – the eye of the storm. We don't get them around the British Isles because they can only form over very warm water (surface temperature of 26.5°C or more), but these remnants of ex-hurricanes can bring gales and high waves – as we saw when Katia passed close to the UK at the start of September. At high tide, high winds can cause destruction with storm surges.

We’re reminded in pages 20–29 of this magazine of the dangers of extreme wind and weather at sea. Loss of life through capsize is a major threat in high winds with high breaking waves and wind heeling – the effect of the wind blowing on the side of the boat and pushing it over.

RNLI all-weather lifeboats are, as the name suggests, able to go out in all weathers. They’re made of sterner stuff than your average leisureboat and wind heeling alone will not capsize an all-weather lifeboat. But if a capsize does happen RNLI Staff Officer Neil Chaplin affirms: ‘All-weather lifeboats are capable of surviving, protecting the crew and carrying on.’ In high winds helicopters can be grounded, but the RNLI volunteers launch to save lives at sea when no one else can help. In 2010 there were 107 lifeboat launches in gale force and storm force winds.

RNLI lifeguards also save lives when the wind wreaks havoc on the beach. High winds create huge waves that knock swimmers and surfers for six, and offshore winds blow unsuspecting inflatable users out to sea and make it harder for those on the water to get back to shore, as RNLI Coastal Safety Programmes Manager Ross Macleod explains: ‘Offshore winds can feel deceptively light behind you on the way out. You only realise how strong they are when you’re exhausted from struggling back to the beach against the wind.’

Deep low pressure systems bring high winds and intense downpours that cause flash floods. The flood water’s too fast flowing to be affected by the wind, but the lifesaving efforts of the RNLI Flood Rescue Team can be hampered by fallen power lines and trees, torn down by the wind.

It bites, it whips and it screams. We understand it better and measure it more precisely than ever, but we cannot pacify the wind. Lifeboat crews and lifeguards will always fight the extreme effects of wind to save lives, but it will forever be untamed.

Demystifying the weather forecast

Key
Temperature in degrees Celsius.
Wind speed and direction in miles per hour. The arrow points the same way as the wind is blowing.

Isobars – lines joining points of equal pressure, like contours on a map. The tighter the lines, the stronger the winds travelling along them.

Depression – another name for a low pressure system.

Prevailing winds – the background overall direction of the wind: south west at the north west edge of Europe.

Jetstream – a band of very fast moving air, about 6 miles above ground. There’s one in each hemisphere and they can stretch around the earth. They move major air masses and affect weather considerably.

In the know

A wind is described by the direction it comes from: a north wind blows from the north.
Downwind – in the same direction as the wind is blowing towards.
Upwind – in the same direction as the wind is blowing from.
Lee – shelter from the wind, provided by, for example, an island or ship.
Wind chill – wind passing over you causes your body to lose heat faster than standing air so temperatures will feel colder than actually measured.

Famous winds

All over the world there are local winds with particular characteristics:
• The Mistral, a cold, dry wind in France
• The Doctor, a daily refreshing breeze in Fremantle, Australia
• Santa Ana, a strong, dry offshore wind in California, USA.