Northeast China experienced an unprecedented sequence of continuous heavy snowfall days in November 2013,the most significant event since 1982—2020.This event was characterized by two intense snowfall processes occurring from the 17th to the 20th and the 25th.The first process had a longer duration,while the second exhibited greater snowfall intensity.This study investigates the causes and predictability of these events from the perspective of the anomalous climatic background of November 2013 and the detailed dynamics of the two intense snowfall processes.The results show that the positive phase of the Arctic Oscillation (AO),the negative phase of the North Pacific Oscillation-like (NPO-like) pattern,increased sea ice growth north of the Barents Sea (November compared to September),and anomalously warm sea surface temperatures in the tropical-southern Indian Ocean during November were responsible for the persistent heavy snowfall event in Northeast China.The increased sea ice growth suggested a heightened release of latent heat flux into the atmosphere,resulting in higher temperatures that favored the strengthening of the positive phase of the AO and the excitation of Rossby wave trains,subsequently weakening the Aleutian low.Moreover,anomalously warm sea surface temperatures facilitated enhanced convection over the tropical Indian Ocean and weakened convection over the tropical western Pacific,leading to a 'cyclone-anticyclone’ circulation anomaly in the Northwest Pacific-Aleutian region,presenting a negative phase of the NPO-like pattern.These atmospheric circulations favored the transport of water vapor from the North Pacific.Additionally,the causes of the two intense snowfalls were analyzed.From the 12th to the 16th,in the five days preceding the first intense snowfall (17th to 20th),the North Atlantic Oscillation (NAO) maintained a continuous positive phase,triggering the persistent eastward propagation of Rossby wave trains.This condition corresponded to a meridional 'cyclone-anticyclone’ anomaly over the Northwest Pacific-Aleutian region,facilitating continuous moisture transport from the North Pacific to Northeast China.During the second intense snowfall on November 25,2013,the Ural blocking high intensified significantly,and the deepening of the Northeast low vortex promoted the transport of warmer and moister air from the tropical western Pacific to the Northeast region,augmenting daily snowfall intensity.Finally,the prediction skill of the anomalous climatic background in November 2013 was evaluated using CFSv2.While CFSv2 effectively predicted anomalously warm sea surface temperatures in the tropical-southern Indian Ocean one month in advance,its skill for predicting anomalous convection in the tropical Indian Ocean and western Pacific,the NAO,and tropical-midlatitude teleconnections was relatively limited.On the subseasonal scale,ECMWF (CMA) reasonably predicted spatial distributions of snowfall for two processes 29 (12) and 13 (16) days in advance,respectively.This prediction skill could be attributed to better anticipation of the daily variations of key circulation systems such as the NAO and the Ural blocking high.Therefore,future efforts should concentrate on enhancing the subseasonal-to-seasonal predictive skills of tropical-midlatitude teleconnections,moisture transport,and the stratospheric polar vortex.