Is there a minimum snow depth to be considered as presence of snow? I want to create a variable "snow cover" with values presence/absence of snow for different weather stations (to work later with NDSI from Landsat images with a pixel size = 100 m). I got snow depth values (cm) from weather stations, but I'm wondering if there is a formula or a minimum depth I should consider as presence of snow. Reading the methods used to estimate snow depth, values are based on different measurements around the station, but it does not specify how big the area is. 

can you please advice on this matter?
A measureable amount of precipitation is considered to be at least 0.01 inch of water. Since on the average 10 inches of snow melt to 1 inch of water, this corresponds on the average to 0.1 inch of snow. Anything less is considered a trace (too little to measure).