Although we haven't had as much snow as London the due to some very cold, dry weather the snow we have had has stayed for a long time. The cold is good for preserving snow but no good for car batteries, which is why my neighbour has had to lay a cable to his garage to charge his battery. This morning I noticed that the snow under the cable had melted so I took a photo. I was wondering if it was the heat dissipated as the current passes through the cable, so here are some wild guesses and inexact calculations

I reckon there must be about 10g of melted snow per cm so the amount of energy needed to melt the snow would be in the region of 3kJ. The current in the wire is probably a few amps, lets say 5A and the resistance of the whole 10m of cable is around 1Ω (I have no idea really, I'm going to have to measure that one). That would make 25W for the whole wire which is 0.025W per cm. So to melt 10g of snow would take about 30 hours. Well the wire has been there a long time but unless the battery is completely dead there won't have been 5A flowing for all of that time. So perhaps its the fact that the wire is black and absorbs radiation from the sun. Well that's about 300Wm^-2 which would give 0.03Wcm^-2 Probably a combination of the two. I know that some people have cables under their paths to melt the snow, these cables probably have higher resistance.