Just to be sure of what you're saying, you have ice forming on the OUTSIDE of the windows, and you don't have ice or moisture on the INSIDE of the windows. Going w/this, ...
The glass is being heated by the inside air sufficiently enough that moisture on the OUTSIDE is condensing and freezing on the 'warmer surface' at the outside of the window. The reason you don't have this happening on the inside is because of the much higher inside temperature which allows the inside moisture to be held in the air as opposed to condensing-out onto the inside glass.
There may be only 2 ways to prevent this from happening. 1) Raise the temperature of your house so high that enough heat transfers THROUGH the glass (to the outside) where a sufficiently small enough 'warm air pocket' is created between the outside glass and outside air to prevent the outside moisture from condensing out onto the outside of the window. (Not likely what you'll end up doing as you may not be able to stand living in a house that's 90 degrees inside!) 2) Install double or triple pane windows.
Unfortunately, what you're experiencing is one of the side-effects of single pane windows. It's always been that way. Storm window covers may help but if you're going to have to 'add' that expense, I'd spend a few more $$$ and buy some insulated windows. My best to ya and hope this helps.