There is a children's nursery rhyme which goes as follows:
Doctor Foster went to Gloucester
In a shower of rain;
He stepped in a puddle, up to his middle
And never went there again.
The verse, it is said, recalls a visit by Edward I of England to that famous city early in the 14th century, where he encountered an excessive and persistent downpour.
Apparently the king's horse became so deeply stuck in mud that planks had to be laid out on the street before it could regain its footing. Edward declared he would never set foot in the town again - although why the tetchy monarch should be immortalised as Dr Foster in the rhyme remains a mystery.
Be that as it may, the ditty raises the important issue of whether it was rain or just a shower which so upset the royal progress. Meteorologists distinguish the two by means of the shape and texture of clouds from which they fall. Rain by definition falls from "layer" cloud - a uniform blanket, covering the whole sky.
Showers, on the other hand, fall from cumulus or cumulonimbus clouds - clouds which form in vertical currents of air in isolated towers, often leaving large patches of clear sky in between; they are recognised by their characteristic cauliflower appearance and result from individual fountains of air surging upwards when the usual "stability" of the atmosphere is upset.
This usually happens because the air near the ground has been heated, making it more buoyant than its surroundings.
Cumulus clouds form in different ways at different times of the year. The most obvious way for the air in the lowest layers of the atmosphere to be heated is by contact with the ground warmed by the summer sun - a process which often results in showers and thunderstorms on a hot and windless summer afternoon.
Alternatively, in more breezy conditions in summer, showers may form when cool air from the Atlantic moves eastwards over the relatively warm surface of Irish landscape. In both cases, the showers become more frequent as you move away from the cool ocean.
In wintertime, the situation is reversed. Then the sea is often warmer than the land and showers are more likely to develop over water as cold air is carried out over the relatively warm sea.
If, however, the wind is onshore, showers which exist over the sea will die out as they cross the coastline; the air nearest the ground, at the bottom of the up-draughts, is cooled by contact with the cold ground, the atmosphere ceases to be unstable, and the shower-clouds disappear.