A clarification - if you happened to be parked downtown somewhere and your car got stuck and you dig out, that spot is for anyone. But on a residential street where there are no driveways or garages, the assumption is that the spot you've dug out is in front of your house. So you're coming home from work (or store, or whatever) and since you can't just "park somewhere else," it's only reasonable to expect others to allow you to have the spot that you've made. Where to park in the interim - that's their problem to solve, but stealing someone else's spot doesn't work. This really only applies in residential areas, so if you dig out to go visit a friend, you should know that you may have to park a ways off and walk, or park on a frozen over parking lot, etc. When is it no longer a "reserved" space - when there's enough melt for someone to reasonably park elsewhere without needing a shovel to get into the spot.