Scott and White Memorial Hospital. v. Fair, No. 08-0970, 53 Tex.S.Ct.J. 703 (Tex. 2010).

As a matter of law naturally accumulating ice and snow is not unreasonably dangerous, no matter what.

If premises owner tries to deice and is negligent, no liability either.  Assumed duty simply does not apply to ice and snow.

See Otis Engineering Corp. v. Clark, 668 S.W.2d 307 (Tex. 1983).