If my employers advise me not to come in because of the weather, it is not taken from my PTO - it's a freebie. That said, I do sometimes work even when my employers are off for a snow day, but in a more flexible way (I might come in a few hours later to wait for the snow to stop, or sometimes I walk to their house and they drive me home in the evening). This is something we worked out between us and wouldn't sit well with every nanny, but it works for me/us.