I would say 20" is a good benchmark for our area. I would say there could be some potential for a heavier ice pack, but rarely. What size pond is your system installed on? How is it fed? Does your siphon continue to flow through January/February?
I would say continuous water movement would be your best chance against an ice plug in the inlet at water level? I say this, but then I think of all the flowing creeks around my place and how they manage to form over with ice during those long cold snaps.
