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Fluctuating snow-covered elevation (FSCE) was conceptualized and proposed to characterize within-year variation of the border between snow-covered and snow-free area in mountainous regions.Two parameters,namely median of snow free period (Tm) and snow free duration (AT),were defined to quantify FSCE.A regression model of FSCE was developed for the Lhasa River Basin,Niyang River Basin,and Changdu region in eastern Tibet.Statistical analysis of the snow-products data with a spatial resolution of 25km×25km shows that:(1) Tm correlates weakly with geographical and topographic factors,having the yearly mean value of July 31; (2) △T correlates signiticantly with the average elevation of the snow-products cell,having the yearly mean value of nearly five months (i.e.,151 days); (3) the region begins snow disappearance in late April and finishes snow coverage in mid November,being snow-free from late June to mid September and snow-covered from December to March in the next year.In addition,snow-products with higher spatial resolution will be helpful to characterize FSCE in smaller spatial scales.