The eighteenth century playwright and poet, John Gay, produced a vivid description of London streets during a heavy summer storm. Here is an extract from 'A Description of a City Shower':

Triumphant Tories, and desponding Whigs,
Forget their feuds, and join to save their wigs.
Now from all parts the swelling kennels flow,
And bear their trophies with them as they go:
Filth of all hues and odours seem to tell
What street they sail'd from, by their sight and smell.
They, as each torrent drives, with rapid force
From Smithfield or St Pulchre's, shape their course,
And in huge confluent join at Snow Hill ridge,
Fall from the Conduit prone to Holborn Bridge.
Sweepings from the butchers' stalls, dung, guts, and blood,
Drown'd puppies, stinking sprats, all drench'd in mud,
Dead cats and turnip-tops come tumbling down the flood.

This colourful picture may give a clue to the origin of the phrase 'raining cats and dogs'. Lexicographers do not agree about its history, but it is easy to imagine that, in any large town or city in centuries past, a sudden downpour following a long dry spell will flush out the remains of hundreds of feral cats and dogs, and no doubt other scavenging animals as well. After the storm, once the floodwaters have subsided, the random scattering of these creatures could lead the more suggestible to believe that it had literally been 'raining cats and dogs'.

We have a large number of other expressions to describe heavy rain in our everyday vocabulary. Most are pretty prosaic, like pouring and pelting; some are rather more metaphorical, like bucketing, belting and throwing, or coming down in sheets or in torrents; others are inappropriate for a column which may be read by children; while some suggest the effect rather than the character of the downpour, like soaking and drenching. Yet others describe the event rather than the rain itself, such as deluge and cloudburst and tropical downpour; there are also a few words from regional dialects which are creeping into the general language, like the northern English 'siling'.

Two rather more colourful expressions which I quite like are 'it's raining stair-rods' and 'it's raining pitch-forks'. It is difficult to see where the business part of a pitch-fork comes into play, unless it describes the angle at which heavy driving rain bounces back from a hard surface. As for stair-rods, I used this in a radio forecast some years ago and was met with blank looks from the other presenters in the studio. Yes, they were under 30, had grown up in homes with fitted carpets, and did not know what stair rods were!

Official weather observers do not have the luxury of the marvellous vocabulary available to the rest of us. Logging the weather on the hour, every hour, they are confined to 'slight', 'moderate', and 'heavy' to describe the intensity of the rain, and 'intermittent' and 'continuous' to indicate its persistence. And each of these words is very precisely defined. Sad, isn't it?