We explain the three different types of rain – and when and where they fall
Mizzle, drizzle, spitting, spotting, shower, downpour, deluge… in Britain, we have many words and phrases to describe rainfall, some of them unprintable. This lengthy liquid lexicon is hardly surprising given that the wet stuff falls here on average once every three days.
What are the different types of rain?
Scientifically, however, rain is classified by how it is generated and there are three main types.
Frontal rain
Frontal rain occurs when a mass of warm air pushed by winds meets meets a mass of cold air, creating what is known as a ‘weather front’. Warm air rises so when it meets the cold, it rises above it, becoming colder in the process and water vapour within it is condensed into larger and larger droplets that eventually fall as rain. Frontal rain can occur anywhere and tends to be characterised by persistent, gloomy grey skies and prolonged rain.
Orographic rain
Orographic or relief rain needs the help of hills or mountains. As warm air is driven towards an upland by prevailing winds, it is pushed up into the cooler atmosphere, where again the water vapour condenses into droplets and falls as rain. This is why hills and uplands are generally wetter than lowlands.
However, in some areas, the orographic effect can create a rain shadow as the rain mostly falls on the side of the mountain it first meets, leaving little or even none to fall on the other side of the mountain. This can create very different habitats and conditions – and the two side of the mountain may be home to very different plants and animals. The Lake District hills, the Pennines, the Scottish Highlands and the Welsh mountains all receive the majority of prevailing winds from the west and create rain shadows to their east.
Convectional rain
Convectional rain is where the beating sun on the ground heats a layer of air above it, causing it to rise. Again, as it heads up into the cooler atmosphere, the water vapour condenses and rain is produced. However, such rain is rarely prolonged and is more likely to produce localised showers.
This accounts for the phenomenon where neighbouring villages can experience sunshine and heavy rain respectively at the same time. How long and how heavy the showers are depends on the volume of air rising and how quickly it rises and this, in turn, depends on the land surface. If the sun is beating on a hard reflective surface, such as roofs or tarmac, more air heats more quickly, producing more rain. Air above a lighter surface, such as woodland or water, heats much more slowly.
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