Met4Cast Weather Guides Section is where you can read and learn about a range of various weather topics at a beginner level. This is a great place to begin if you are learning about GCSEs.



What is Weather - Introduction
Weather is the day-to-day meteoorlogical condition of a certain place at a certain time measured in terms of wind, precipitation, clouds, atmospheric and ground level temperatures.

Meteorology is the study of Earth's atmospheric conditions. Meteor comes from the Greek word "Meteoron", which means "high in the sky". The "ology" part of the word means "the study of...". In this context, the study high in the sky is the atmospheric conditions, which are high up.

From the above statements, you can already tell that they are very similarly linked. However, there is one difference you must remember. Weather must include, "day-to-day, place and time".

You can predict the weather by examining the atmospheric conditions using weather charts and satellites. You can also predict the weather by gathering sea temperatures. Forecasting weather is a very difficult process, especially for long range and isolated events such as tornados.

High Pressure
High Pressure is a mass of air pushed against the Earth. This is because cooler air particles are packed together forcing dence air to form and exert pressure on the Earth.

High Pressure is usually a large and slow moving area of pressure. The winds circle around the pressure in a clockwise direction, known in atmospheric terms as "anticylonic movement". High Pressure often brings calm weather with very little wind.

As the air sinks, it warms closer to the surface preventing condensation and clouds forming. This is why we are more likely to see sunny calm days in High Pressure than in Low Pressure. However, if the air is very warm at the surface, it can rise and form a layer of cloud or even drizzly rain.

No type of air pressure can mean hot or cold conditions but the air direction can force the different air temperatures to become established.

High Pressure over the Azores in Summer indicates warm or hot conditions quite often. This is because on it's northern flank, the air moves clockwise with air coming from the Gulf Stream near Mexico. If the pressure pushing further west across Spain, then we can pick up some very hot conditions from the south, like we did in the Summer of 2003.

High Pressure sitting over Scandinavia can bring very cold conditions across the UK depending on if the pressure is elongated or vertical. If it is elongated, then the southern flank of the pressure forces eastily winds to develop across the UK. This is a very cold direction in Winter and very hot in the Summer. This is due to the fact Russia is a large continent and substains a similar temperature throughout a season. Russia and Sibera are very cold during winter and if the UK picks up air from that direction, then a severe cold snap occurs.

Low Pressure
Low Pressure is a mass of air weakly pushed against Earth because it is being warmed and becomes less dense. It is formed by warm air passing near cold air higher up. As the warm air rises, water vapour in the atmosphere condenses into clouds.

Low Pressure usually brings cloudy, wet and windy conditions almost all the time. The precipitation that forms due to clouds forming is found on a weather front which is a boundary between the warm and colder air.

Low Pressure can easily be spotted on a weather chart by its large number of tightly packed isobars. Isobars are lines on the chart that indicate equal gradients of air pressure. The closer the lines are, the stronger the wind is.

A Warm Front usually brings a change in weather from cool or cold conditions to warmer conditions. The warmer air rises above the cold air forcing clouds to form. You can spot a warm front on a weather chart by semi-circles along a line. The base cloud of a warm front is altostratus and is a thin sheet to back up the moisture. Below this stratus or nimbostratus form and rain will fall.

A Cold Front usually brings a change in weather from warm conditions to cool or colder conditions. The warm air is forced steaply above the cold air. Cooler air undercuts the warm air allowing cooler conditions to develop and large clouds to form. Cumulous or Cumulonimbus clouds form on cold fronts due to the unstable air masses. Cumulonimbus are known as thunder clouds and are very tall. They have an anvil shape and can produce very severe and dangerous weather if convection is high. A Cold Front usually brings a very large amount of rainful at fast rates. You can spot a cold front on a weather chart by the triangles along a line.

Snow
Snow is a type of precipitation that falls from clouds in the form of ice crystals. Snow crystals are six sided, known as hexagonal. Precipitation very often falls as snow crystals through the atmosphere but melt and turn to rain on the way down to the surface during a typical mild day.

When the temperature at the surface is cold enough - let's say below 4c, snowflakes will fall. If the ground is cold enough, usually when there has been a series of frosts, then the snow will settle if heavy. There are two main types of snow, dry snow and wet snow.

Dry snow is caused when the temperature is extremely cold. During very cold conditions, the atmosphere becomes slightly dryer. When dry snow falls, it isn't actually dry but is more powdery and unlikely to settle as well.

Wet snow is the most common type of snow and usually brings larger accumulations. This is caused when the temperatures are near freezing point at the surface. The snowmelts slightly as it falls through the atmosphere but stays as snowflakes as it settles. Wet snow may not always setting, for example if it melts too fast due to warmer temperatures at the surface, it may fall as sleet.

Lake effect snow is when cold and dry Arctic winds move across warmer lake water and picks up lots of moisture. There is usually a very narrow band of heavy snow. This type of snow is common by the Great Lakes in America during winter and is quite rare elsewhere.