If, therefore, we devote sufficient funds and effort to obtaining weather messages from a wide area, we may chart the weather on suitable maps, study how the patterns move and change, and predict by extrapolations. Although there are many complications due to such factors as diurnal variations, mountains and valleys, land and sea distributions, man made atmospheric pollution and a host of natural peculiarities in the behaviour of the atmosphere itself, the simple facts about the behaviour of depressions and anticyclones (outside the tropics) have made forecasting possible. At the same time they have made great improvements in forecasting seem almost impossible.