When summer air conditioning contributes significantly to an electric utility's system peak load, it is useful, for load forecasting purposes, to separate total system load into two components: temperature-sensitive load and nontemperature-sensitive load. Examination of historical data indicates that temperature-sensitive loads depend not only upon coincident but also antecedent weather conditions. Regression analysis techniques using a digital computer have shown that the combined effect of these weather conditions can be expressed by one composite weather variable (WV). Total system load can then be expressed as Basic Load plus the product of WV times a coefficient of air-conditioning saturation. Results obtained by application of this method to historical data (1949-1964) of Public Service Electric and Gas Company are presented.