Abstract: The physical basis of long-range forecasting has been examined in this paper and reasons have been given for and against the employment of a certain method in long-range forecasting. The methods examined are (a) weather cycles and periodicity; (b) statistical method based on the variation of solar radiation and this icnludes the variation of the number of sunspot and the variation of solar constant; and (c) statistical method based on centres of action.Crest emphasis has been laid on the relation between the general circulation of the atmosphere and the variztion of salar radiation and it is suggested here that big stride can only be made in long range forecasting when the relation between the general circulation and solar radiation is tvell understood.