Maybe you can find something to boost the speed of the warm air. In the shop where I work (which is heated), we use an old furnace squirrel cage at floor level aimed at our service vans. The snow on the surface and packed underneath melts or falls off in no time.I am not sure it will melt off much snow, I think Dave will prove correct on that score.
Maybe one of those big barn fans would do the job. But the squirrel cages work great for us. Might be worth experimenting.