THE Oxford Dictionary tells us, with quite remarkable precision, that the word "forecast" has been in use for "weather prediction" since 1673, but meteorologists refute this theory quite emphatically. Loyal to a man and woman to their predecessors, they maintain that the special meaning of the word was devised in 1860 by Vice Admiral Robert FitzRoy, the father of modern operational meteorology in these islands. Given the special task of providing "storm warnings" for naval and merchant ships around the coasts of Britain and Ireland, he was anxious to avoid "the somewhat unfortunate connotations attaching to such terms as prognostic and prophecy", and therefore decided to call his bulletins "weather forecasts".
Meteorologists are still very fussy about the words they use in shipping forecasts. To the casual listener, words like "soon" and "later" might seem to tell us merely in a very general way how quickly we might expect a sudden disimprovement, or improvement, in the weather. But these, and similar words, have a meaning which is quite precise "Imminent", for example, means within 6 hours "soon" is between 6 hours and 12 and "later" means that the change will take place in 12 to 24 hours time.
There is a similar hierarchy of precision when it comes to describing the speed of movement of the weather systems. If, for example, a front or a depression is said to be moving "slowly", it means that it is travelling at a speed of less than 15 knots 15 to 25 knots is described as "moving steadily", and 25 to 35 is "moving rather quickly". A system travelling at 35 to 40 knots is "moving rapidly" and if it is even faster it is "moving very rapidly".
"Fine", "fair" and "cloudy" are terms used to describe conditions that are uneventful when the weather is dry and generally good. But they, too, have subtle shades of meaning "cloudy", as the word implies, means that the sky will be covered, or very nearly so, with cloud "fine" is used when very little cloud is expected, and the forecast will specify "fair" if cloud is expected to cover between about one third and two thirds of the sky.
In the case of visibility, the relevant words are "good" and "moderate" and "poor". The first implies that you will see further than five miles, "moderate" is from two to five miles, and "poor" indicates a visibility from two miles down to 1,100 yards. And finally, a visibility of less than 1,100 yards is "fog".