To add a bit more science to Izzy's response, the molecular structure of dry ice prevents you from packing the flakes you get from the tank/burlap bag into a solid slab of dry ice. When you put ice under pressure it converts to liquid a little bit then refreezes as a solid mass. That's what allows ice skates to slide across the ice. No other material acts in quite that same manner. The flakes will evaporate away much, much quicker than the solid slabs because the flakes have a much greater surface area from which to evaporate.

The idea of keeping a CO2 tank system to make dry ice on demand sounds doable, but I have to wonder about the economics. I think it'd be cheaper just to get the dry ice if a storm is coming. Of course, this only works if you know a storm is coming...

-Blast