Multivariable Lagged Regressive Model of Low Frequency Rains over the Lower Reaches of Yangtze River Valley for Extended Range Forecast in the Early Summer of 2013
Lowfrequency rainfall over the lower reaches of Yangtze River Valley (LYRV) and the principal component of 850 hPa meridional wind anomalies over the extratropics of the Southern Hemisphere are employed to construct a multivariable lagged regressive (MLR) model, which is applied to the daily forecasting of low frequency rainfall over LYRV in June-July of 2013 for the extended range forecast. The result indicates that this method for the 20-30 d lowfrequency rainfalls over LYRV has good predictive skill up to 25-30 d. By many hindcast experiments during the period of 2001-2012, this MLR model for the 20-30 d rainfalls over LYRV has good predictive skill up to about 30 days for the years with the stronger or normal 20-30 d oscillations. Based on the development and evolution of the southern circumglobal teleconnection (SCGT) wave train, it will help us to forecast the process of lasting heavy rainfall in early July of 2013 over LYRV over 20 days in advance. Hence, the low frequency variability of extratropics over the Southern Hemisphere is one of the main factor of the changes of the heavy rainfall over LYRV in early summer for the extended range.