I will say this, that snow better get to melting!
Tracy, do you anticipate existing snow will change your plans for paint? I wouldn't think it would be possible to paint on the snow. When it melts or gets down-trodden it would make an ambiguous line, at best.
Yes, obviously white paint on snow won't work. However, my plan is not to paint the OB's until tomorrow afternoon. By which time, fingers crossed, all the snow will finally be melted. There is only 2-3" left. Even if some snow lingers where the lines are to be drawn, I will deal with it in one way or another. Also, I'll be flagging up the lines. So if, for some reason, a line becomes indistinguishable in the area of concern, just use two flags to determine OB between them.
Everything is going to be fine. Unless you're an OB hater, in which case, things are going to be even better... for my enjoyment.