**6. Conclusions**

Snow cover is one of the most active features on the land surface [46], and it is very important to quantitatively explore and understand snow phenology variations for local climate change. The snow phenology variations and their driving factors in Northeast China from 2001 to 2018 were assessed based on daily cloud-free snow products generated in this research. The conclusions were as follows.


**Author Contributions:** Conceptualization, H.G. and Z.G.; methodology, H.G. and X.W.; software, H.G. and Z.G.; validation, H.G., S.C.; writing—original draft preparation, H.G.; writing—review and editing, H.G., X.W., Z.G. and S.C.; supervision, X.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Science and Technology Basic Resources Investigation Program of China gran<sup>t</sup> number 2017FY100500 and the National Natural Science Foundation of China gran<sup>t</sup> number 41771373, 41971325.

**Acknowledgments:** We gratefully acknowledge the Google Earth Engine, the National Earth System Science Data Center and the National Cryosphere Desert Data Center for obtaining data freely. Moreover, we would like to thank the two reviewers for their valuable comments and suggestions.

**Conflicts of Interest:** The authors declare no conflict of interest.
