Forecasting precipitation over Delhi during the south-west monsoon season

The south-west monsoon (June-September) is the major rainy season over Indi a. Information about the occurrence of precipitation and the expected quant ity at a specific place is important in many sectors of human activity. In this study, objective methods are developed to forecast the probability of precipitation (POP) and provide the quantity of precipitation forecast (QPF ) over Delhi. As the onset of the monsoon at Delhi is around 30 June, the m odels are developed for the months of July, August and September (JAS) usin g surface and upper-air data period 1985-90 and tested with data from JAS f or 1994 and 1995. A multiple linear regression equation is developed to for ecast the POP and multiple discriminant analysis is used to produce the QPF in terms of one of four groups (0.1-1.0; 1.1-10.0; 10.1-30.0; and greater than or equal to 30.1 mm). The QPF model is used only if precipitation is e xpected to occur (the POP forecast is turned into a categorical forecast). The categorical forecasts based on the POP exhibit positive skill scores co nsistently with both the development and independent data sets. The model f or QPF also performed satisfactorily.