Unfortunately, neither life nor the weather are simple or clear-cut and there are times when the forecaster may be in some considerable doubt as to precisely which sea areas will get gales within the forecast period and, indeed, whether the winds will reach gale force at all. There is no point in crying wolf and yet he has to be able to give some warning or indication of the uncertainty. This is may seem somewhat pedantic to many of us, since it is as good as a warning of a gale and many would not set off on a long crossing, say across the North Sea. Many sailors in our relatively slow moving boats, would like to see warnings issued beyond twenty-four hours. The basic problem, in physical terms, is the classical one of predicting the difference between two large quantities.
Wind is caused by relatively small differences in barometric pressure.
A small rise in the pressure over Northern France and a slight fall over Ireland could make all the difference between a nice force 4, an uncomfortable force 6 and a three reef, storm jib force 8.