THOSE many readers of Weather Eye who took the opportunity to hear Oasis at the Point may well have caught the opening lyrics of their number Some Might Say, which, as we know, is Track 7 on the album (What's the Story) Morning Glory?:
Some might say that sunshine follows thunder;
Go and tell it to the man who cannot shine.
Well, have these phenomenal Gallaghers got it right? Is it true that thunder is often followed by the sun? As so, often happens when we talk about the weather, we can only say "It all depends!"
Thunderstorms occur when the atmosphere becomes, as we say, unstable - when the temperature falls very rapidly with height. In such a situation any volume of air subjected to a slight upward movement finds itself much warmer, and thus lighter and more buoyant, than its surroundings. It therefore continues to accelerate rapidly upwards, resulting in a powerful vertical current - a jet of air rising like a great invisible fountain.
It is these atmospheric fountains that give rise to cumulonimbus clouds, and in extreme cases to the electrical processes in which thunder and lighting have their origins. There are number of ways in which the necessary instability can be brought about, and the likelihood of sunshine in the aftermath varies with the situation.
One way in which the atmosphere can become unstable enough for thunderstorms to occur is when cold air is carried down towards Ireland from the region of Iceland or Greenland in a north westerly airflow. As it flows south eastwards to lower latitudes, the air travels over seas which become progressively warmer: the warm water heats the lower atmosphere in contact with it without affecting the air some distance above the surface, and the instability required for thunderstorms may well occur. If so, the indivi dual thunder showers are usually dotted here and there, with clear skies in between through which the sun may very often shine.
Another trigger for thunderstorms is often the heating of the land - and hence the air immediately above it - by the hot sun of a humid summer afternoon. Here too, the thunder showers are localised, and the sun returns as soon as they drift away. But thunderstorms are also common near the cloudy centre of a deep depression, which is itself a extensive zone of rapidly ascending air. Here rain and thunder may persist for many hours, and the nearest patch of blue through which the sun might shine may well be more than 100 miles away.