Extended-Range Forecast of the Beginning of the Rainy Season in Yunnan by Studying the MJO Action Regularity

When the rainy season begins is always a significant issue in Yunnan's forecast of weather and climate. The extended-range forecast for the beginning date of rainy season is urgent and necessary, especially in the case of extreme droughts in Spring and early Summer in Yunnan occurring frequently for the past few years. Thus, based on doing extended-range forecast of precipitation through the winter half-year in Yunnan using the patterns of MJO activity, and combined with early research findings about the relationship of the tropical low-frequency to the rainy season in Yunnan, the extended-range forecast for the beginning date of the rainy season has been fully studied and examined. The results suggest the points below: (1) The precipitation trends can be forecasted by the wet and dry windows phase that would impact water vapor transportation of Yunnan which corresponds to the position of the action center of MJO. (2) In our previous research we found some key areas which had exercised an inf l unce on the convection of the wet or dry years in Yunnan. The index of spring’s precursory signal in the key areas is effective to forecast the beginning of the rainy season. Thus, using both MJO moving regularity and precursory signal in the key areas is an effective way to improve prediction of the beginning date of the rainy season.