## 5 Conclusions  
According to our results, in the cold periods of 2019-2021, the main factors controlling the change in the initial isotopic composition of water (\(\delta^{18}\)O and \(\delta\)D) in the layers of seasonal snow cover in the south of Western Siberia are the existence of a vertical (between layers) temperature gradient, which contributes to the vertical \"smoothing\" of the isotopic composition within the snowpack, and the influence of soil moisture, which enriches the bottom layer of snowpack in heavier isotopes. Soil moisture has the most significant effect on the bottom layer of snowpack in contact with unfrozen soil. During the winter period, the sublimation of the upper layers of snowpack is observed only at the moment of a sharp increase in the daily air temperature. At the end of winter, with an increase in solar radiation, the contrast between day and night air temperatures determines the shift in the isotopic composition of the top layer of snowpack, relative to the initial snowfall, towards its enrichment in heavier isotopes (a temperature difference of less than 10 degrees, as per the top snow layer in 2019-2020) or depletion (a temperature difference over 15-20 degrees, as per the top snow layer in 2020-2021).  
**Supplementary Materials:** The following are available online at [[https://www.mdpi.com/article/10.3390/app12020625/s1](https://www.mdpi.com/article/10.3390/app12020625/s1)]([https://www.mdpi.com/article/10.3390/app12020625/s1](https://www.mdpi.com/article/10.3390/app12020625/s1)), Figure S1: Sampling site on the roof of the building of the Institute for Water and Environmental Problems of the Siberian Branch of the Russian Academy of Sciences (IWEP SB RAS) (a) Snowfall's event-based collecting; (b) getting the snow layers from a plastic barrel (experiment No.1), Figure S2: Local meteoric water lines (LMWL) for winter (a) 2019-2020 and (b) 2020-2021. Blue-event-based precipitation, black-snowpack (bulk), green-bottom layer of the snowpack on a non-frozen soil, red-bottom layer of the snowpack on a frozen soil, Table S1: The statistical estimates of LMWL for snowpack and snowfall samples getting in Altai region in winter 2019-2020 and 2020-2021 (Ordinary least squares regression (OLSR) was applied), Table S2: The daily average air temperature and difference between day and night air temperatures during the formation of layers of the snowpack (Experiment No. 1 and No. 2).  
**Author Contributions:** Conceptualization, T.P.; methodology, T.P. and A.E.; investigation, A.E. and T.N.; writing--original draft preparation, T.P., A.E. and T.N.; writing--review and editing, T.P.; visualization, T.N. and A.E.; resources and funding acquisition, T.P. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by Russian Foundation for Basic Research (RFBR), grant number 19-05-50057.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The datasets used and analyzed during the current study are available from the corresponding author ([PERSON]) on reasonable request.  
**Acknowledgments:** The authors are grateful to the researchers of the Institute for Water and Environmental Problems of the SB RAS [PERSON], [PERSON], and [PERSON] for their help in the field work on sampling the snowpack and [PERSON] for help in statistical analysis of regression equations.  
**Conflicts of Interest:** The authors declare no conflict of interest.