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The snow capital of China in the Altai Mountains, which is located in the northernmost part of Altay Prefecture in Xinjiang, experiences many Warm-Sector Snowstorms in winter due to the frequent southward movement of the polar front area. These snowstorm disasters sometimes cause more harm to the national economy and people’s lives than rainstorms, often resulting in huge losses to transportation, animal husbandry, electricity, etc. Meanwhile, in order to improve the service level of ice and snow tourism forecast in Xinjiang, it is necessary to actively explore the characteristics of water vapour during the winter snowstorms in the Altai Mountains. Based on the solid precipitation data and NCEP/NCAR reanalysis data of the Altai Mountains, the circulation background and water vapour characteristics of three snowstorms in the Altai Mountains in 2021 are analysed using synoptic diagnosis and different water vapour analysis methods. The results indicate that: (1) The three snowstorm processes are typical of the warm region of northern Xinjiang. The snowstorms mainly occur in the divergence area on the right side of the southwest (by the west) jet axis at the upper level, the southwest (by the west) frontal area at the bottom of the polar vortex, the convergence area in front of the outlet area of the southwest jet at the lower level, and the overlap zone of the surface decompression and temperature rise. (2) The Euler’s method analysis shows that the water vapour in this area mainly comes from the Atlantic Ocean and its coast. The western boundary of the Altai Mountains is a water vapour input, and the eastern and southern boundaries are water vapour outputs. The water vapour input in the middle and lower layers is closely related to the quantity of snowstorms. The convergence area of water vapour flux divergence is located in the lower troposphere. (3) The HYSPLIT’s (Lagrange) method analysis shows that water vapour mainly come from the Arctic Ocean and Europe, followed by Central Asia and Canada, significantly differing from the above conclusion; the water vapour in the lower troposphere makes a significant contribution to the overall snowstorm area. (4) The contribution model of water vapour for the snowstorm process in the Altai Mountains is constructed. When the water vapour of 700 hPa and above reaches the key area from the source, it mainly enters the snowstorm area from the west (southwest) path. When the water vapour of 700 hPa and below reaches the key area, it primarily enters the snowstorm area from the southeast path when the circulation is appropriate, but the contributions from the west (southwest) and northwest paths cannot be ignored; water vapour mainly accumulates in the lower troposphere and converges and rises.