Characteristics of medium range rainfall forecasts of the Asian summer monsoon

Mean characteristics of the rainfall forecasts produced by the global data analysis–forecast system of India are examined for the summer monsoons of 1993–1996. Further, daily rainfall forecasts (accumulated for 24 h) extending from day 1 to day 5 are utilised to compute monthly/seasonal mean forecast fields to study their consistency and reliability. Global patterns of rainfall forecasts are also compared with the large scale rainfall climatological fields. In addition, observed rainfall distributions over India are used for regional verification of the medium range rainfall forecasts. The forecasts appear to reproduce most of the large scale features of rainfall, except the sharp gradients over the Deccan plateau (leeside of the Western Ghats—west coast mountains over the south of Peninsular India) and the Gangetic plains over the north of India. Further, it is found that the forecast model has a characteristic tendency to reduce the quantum of rainfall over northwest India and the north Indian plains to the south of the Himalayas. In addition, in this study, certain aspects of the year‐to‐year variability of the predicted rainfall fields and their associated characteristics are examined along with the other systematic errors of the model. It is found that in this case, the sources of systematic errors could at least partially be eliminated, the rainfall forecasts up to day 3 or so can become a very useful product of interest. Copyright © 1999 Royal Meteorological Society