Weather FAQs

Is it warmer now than when I was young?

If we look at the 20th century we find that seven of the top ten warmest years of that century occurred in the last decade. The warmest year on record was 1998 and analysis of tree ring growth data shows it was the warmest year since 1000. The average UK temperature has increased by over half a degree centigrade in the last 150 years. Whether human activities or natural phenomena are responsible for this global warming is hotly debated, although the general scientific consensus is that human activities are influencing the climate.

Did we have more snow when we were children?

If you were a 60s child you will have had on average 20 snow days a year. This was roughly halved during the 70s and 80s. The children of the 90s only saw an average of 5 snow days a year. The winter of 1962 to 1963 was the coldest of the 20th century.

Snow requires the air temperature high within the cloud to be below freezing so ice crystals can form in the clouds. The snow turns to sleet if the air temperature nearer the ground is above freezing. It is not surprising that there has been less snow over this period as the climate has become warmer, even in the winter.

What exactly is a pea-souper?

It is a very thick smog – a mixture of fog with particles of black smoke and sulphur dioxide. The particles cause fog to form by providing a surface for the condensation of water. London in the 1950s saw pea-soupers so thick that you could not see your hand held out at arm's length.

Smog was particularly bad in the past because many homes had open fires and they burnt sulphur-rich coal for heating. The sulphur dioxide made the smog incredibly smelly and gave it a yellow appearance. The worst of these smogs was in 1952 when 4000 people died – this led to the Clean Air Act 1956 in an attempt to control domestic sources of smoke.

What's the difference between fog and mist?

Both fog and mist are water droplets that have condensed because the saturated air has become cold. They are effectively low lying clouds. The difference between them is their thickness. With a fog, the visibility is less than one kilometre, whereas with a mist, the visibility must be at least one kilometre.

What is black ice?

This is transparent ice that forms when water freezes on top of freshwater or dew, normally on a road surface. It is actually transparent but is termed black because it does not show on the road surface like the white ice we can see. White ice has many internal irregularities, caused by air bubbles, which reflect the light entering it back out in all directions so it appears white. Black ice does not contain these bubbles and allows the light to pass all the way through. The light bounces off the road surface and back through the ice so all you see is the road.

Why is the night freezing after a sunny day?

On a sunny day there are no clouds, and the energy coming in from the Sun can fall unhindered on the Earth's surface, quickly heating it up. although clouds block light from the Sun, they also act like a blanket, helping to trap any heat that the Earth gains. So at night, if there are no clouds, the heat energy is easily lost to space and it becomes cold.

The greenhouse effect is caused in a similar way. Greenhouse gasses in the atmosphere trap heat and prevent it escaping to space. The more greenhouse gasses in the atmosphere, the less heat escapes, so the more the planet is warmed.

Why is it always windy by the sea?

The land and the sea heat up and cool down at different rates and this causes strong winds. During the day the land will absorb heat from the Sun far more quickly than the sea. This causes the air above the land to rise, drawing in the cooler air from the sea and creating a cool sea breeze from the sea to the land.

The reverse happens at night. Because the land cools down more quickly than the sea the air sinks, pushing the air beneath it out to sea and the breeze goes from the land out to sea.

What are fronts?

Fronts are the boundary between different air masses. These 'blocks' of air have different temperatures and origins. They are classified by the direction they are travelling in, the type of air they carry and how developed they are.

Warm fronts have warm air behind the boundary and cold fronts cold air. Warm fronts may bring rain and gentle breezes. Cold fronts can create storms and gusty winds.

Occluded fronts occur when cold air moves under cool air or where cool air rises over cold air coming in. They bring cumulus (white or grey cotton wool clouds) and gentle winds with rain or snow.

The fronts are moved about by winds and when one front meets another they inevitably clash. One front will be forced to rise while the other cuts below it. However, this does not happen with a stationary front, where cold and warm air masses come together but neither advances on the other. The result is a period of steady and unchanging weather.

Why is it so wet in the UK?

The prevailing winds in the UK are from the west. So as the wind blows over the Atlantic Ocean the air picks up water. Air can only hold a certain amount of water vapour – it can hold more when it is warm than when the air is cold.

When the air from over the Atlantic reaches the UK it has to rise over the top of the mountains. As the air rises it cools and so the amount of water vapour the air can hold drops dramatically. The water vapour starts to condense out into clouds and as the drop size rises, rain become increasingly likely. Air rising over the Pennines is a wonderful example of this, and the reason why it always seems to rain in Manchester.

What causes flooding?

Rivers are accustomed to carry a certain amount of water, and heavy rains or snow melting will increase the level causing them to flood their banks. Normally this water overflows onto a natural flood plain. If houses are built on these areas they are liable to be flooded. In some areas there has been a tendency to build houses on unsuitable areas without proper flood defences in place.

The north of England has had increasing amounts of persistent heavy rain, the major cause of flooding, and this is predicted to increase with the changing climate. But heavy rain and floods in the winter don't necessarily mean a drought-free summer. Unless the rain falls where the reservoirs are, the excess water will just drain away into the sea leaving us all with the prospect of yet another hose pipe ban.

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