Regression Forecasting of the Onset of the Indian Summer Monsoon with Antecedent Upper Air Conditions

Abstract It is shown that the recorded onset dates of the summer monsoon in southwestern India can be closely related functionally to the antecedent upper air conditions. The antecedent upper air conditions are represented by April mean values of the daily upper air parameters at 100 and 700 mb from 1958 to 1978. It is further demonstrated that the multi-regression scheme on the basis of such a functional relationship may be utilized in an objective forecast of the onset date. The forecasted dates are shown to be reasonably close to the recorded onset dates. Various aspects of the approach and scheme are discussed. Because of the time variations of the patterns of the general circulation, a constant updating of the regression equation should be an integral part of the multi-regression forecasting scheme.