The approach to produce MOS probability forecasts of moderate and heavy .precipitation is shown in the paper. So are the conditions to narrow sample size, design and derivation of predictors, procedure to adjust the forecast probabilities as well as verification and reasons for errors. And it expounds how the fields on a surfaces from model forecasts used as predictors, two dimensional interpolation, and variables' changes are made and employed in MOS forecasting. Their effects on MOS forecasts are also explained.