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One suggestion:
You can use openstreetmap as a background map using Leaflet library, https://leafletjs.com/ which allows you to serve maps on the web and add any layers you are interested in to present in the map.
With Leaflet you can easily deal with the polygons that represent the snow areas. To define those areas you can use e.g. geojson.io t, so that you can integrate the relevant data (in your layer(s)) that is meaningful to you (Leaflet loves GeoJSON). It doesn’t make sense to place this data on the OSM map as it doesn’t represent the terrain.
Depending on the interaction with the map you need, you must have javascript knowledge.
Leaflet is a rich library that allows you to control easily objects you put on a layer.
To interact with the map you can take a look at the additional plugins provided to Leaflet, some will help. To deal with GPX you can take a look at https://github.com/mpetazzoni/leaflet-gpx .
If you find any errors or improvements to do on the OSM map in your area, you can just edit the map in its homepage.
Your project sounds interesting :slight_smile: