The problem in urban Fl is not ice, its acid dew. When the moisture droplets dry the pollutants in the air leave little blemishes in the lens coatings. I use lots of water, and a clean, soft, fine weave cotton cloth (like old Y-fronts or t-shirts)to gently swish the water off (no pressure). You have to be careful no moisture gets in the air space of the doublet, or you have to dismantle the entire objective. Capillary action will cause it to scoot across the entire space between the two elements.

With mirrors, I just submerge it in a pan of distilled water and drag the cloth across the mirror, without actually touching it with my fingers or applying any pressure other than the weight of the cloth itself.