I have 10 singleband rasters of the snow cover extent (1 raster/day from 1st of December to 10th of December). I have to create a composite image that merges all of them. I tried the r.composite tool from GRASS and the Build Virtual Raster tool, but I don't really understand the results. The raster values are from 20 to 200:

20 - sea, 21 - lake, 22 - river, 30 - cloud, 100-200 - % of the SCE (example: 154 = 54% snow cover).

One of the input rasters:

Output raster:

I really don't know if the output is correct. Some of the rasters I have are very cloudy so that would explain the large cloud area on the output image. Is this how you create a composite raster in my case?