The first snowstorm event occurred in Jiangsu during January 3-5, 2018 had larger snowfall but lower snow accumulation efficiency, while the following second snowstorm event during January 24-28 had smaller snowfall but higher snow efficiency. Using the ERA-Interim reanalysis data and the observation data from the China Meteorological Administration, this study investigated the temperature and humidity conditions in these two snowstorm events and explored the underlying physical processes in the framework of isentropic atmospheric mass circulation. Main results are as follows: (1) The early stage of the first snowstorm event was characterized by higher temperature in the entire troposphere, which was attributed to a relatively deeper and stronger poleward warm air branch of isentropic atmospheric mass circulation to the south of Jiangsu, compared to the second snowstorm event. In contrast, in the second snowstorm event, the stronger equatorward cold air branch of isentropic atmospheric mass circulation resulted in the temperature lower than 0℃, which promoted the higher snow accumulation efficiency. (2) The deep water vapor convergence layer in lower isentropic layers collaborated with the wide range of ascending motions during the first snowstorm, and further brought lower-level water vapor to higher layer for the formation of larger snowfall. Larger meridional water vapor transport but weak zonal water vapor divergence in the low isentropic layers caused the near-ground specific humidity to increase significantly and thus contributing to the lower snow accumulation efficiency. However, in the second snowstorm event, there was a deep layer of water vapor divergence in the lower isentropic layers, which contributed to the larger snow accumulation efficiency. Therefore, colder and dryer conditions resulting from the abnormal meridional cold air transport and weak water vapor transport in both meridional and zonal directions are the key factors for the higher snow efficiency in the second snowstorm event. The comparison of spatial distribution of temperature and humidity with that of the snow efficiency further shows that the snow efficiency is more sensitive to the local temperature and humidity under the condition of high temperature and humidity.