Sub-seasonal prediction of the 2008 extreme snowstorms over South China

Extraordinarily frequent and long-lasting snowstorms affected China in January 2008, causing extensive social and economic damages. The potential predictability of such extreme events on the sub-seasonal timescale has been evaluated using results from the hindcast experiments by the Beijing Climate Center Climate System Model. The spatial distribution of precipitation during the period can be successfully reproduced with a 10-15 days leadtime, although the intensity is weaker than observations. The model's success lies in the timely prediction of large-scale atmospheric circulation anomalies, such as the atmospheric blocking over the mid-high latitudes and the southwesterly flow associated with the Bay of Bengal trough in the low latitudes, but the predicted cold air is too strong while the warm air too weak, leading to an underestimation of precipitation along the main rainbelt. Meanwhile, the capture of those circulation anomalies in the initial states and their persistence in subsequent model predictions has played a key role in the predictability of such an extreme event. Detailed analysis has shown that sea surface temperature and low-frequency signals, such as the Arctic Oscillation and the Madden-Julian Oscillation, may also be important during the process.