I have had an opportunity to test non-mapping Garmins in fog, at least, on San Miguel Island where the west end research station gets its gray water from a spring about a mile and one half away. The water is carried on the backs of the researchers, usually after work hours, often in darkness and fog. There is no established trail, by intention. You can keep your bearings by orienting to the constantly NW blowing wind, which courses over relatively flat, featureless terrain.

I tried it once without either compass or GPS, and did pretty well, coming in about 150 off from the station, nearly missing it until someone opened a door, providing a homing beacon.

On another try I used a GPS, setting a waypoint and then following it back from the spring. It was realy amazing to see the station materialize out of the fog dead ahead when fifty yards distant. I soon got in the habit of setting a waypoint every time i left from a vehicle when on the islands.

I have no experience using a GPS in blowing snow and cold, but those factors roughly triple the difficulty of doing anything. I'll bet using a GPS would be very tricky....