The spatial organisation of daily rainfall in eastern New South Wales

Product‐moment correlation are used to provide an estimate of the degree of association of daily rainfalls between a number of sited in eastern New South Wales. Completely dry days are omitted from the analysis so that the coefficients obtained represent the strength of association between sites for days on which rainfall occurs. Maps showing the strength of links between sites are used to illustrate general trends in the spatial organization of daily rainfall on a monthly basis. Certain very district seasonal changes in rainfall patterns emerge, principally distinguishing the summer (December to February) from the cooler part of the year (April to October) in terms of the nature of association and the separation of discrete rainfall areas. Many of these comprise groups of two or three Bureau of Meteorology forecasting areas. More widespread rainfall associated with lager‐scale atmospheric disturbance occurs in February, and in April and May, but during the April to October period the Divide is seen as a very important climate, as well as topographic, feature. At other times smaller topographic units apparently exert a control over rainfall occurrence. This is particularly true of the Hunter valley which is the center of rainfall development for a wide area in January. Sea breeze front effects are also seen as important enhancers of rainfall in the summer.