blind landing areas
Dcorp, they are for landing ski equipped aircraft in conditions that are not suitable for the skiway (which have flags and other markets).
Besides the obvious blizzard, this might be due to BLSN that obscures the ground with blue sky above. The depth depends on the wind strength and temperature and type of snow.
It's basically setting up a straight shallow nose up approach with a low descent rate and chopping the power when you feel a bump. The rad alt is not accurate enough for flaring due to variations in snow reflectivity. Good 'fun'.