Just in case you take a bad fall this winter... I think you ought to know what your rights are. I reviewed some of the cases in Washington State, and this is what I came up with:
Since 1975, landowners have been required to "exercise reasonable care [toward invitees] to prevent the occurrence of defective or dangerous conditions" regardless of whether the dangerous condition was a "natural" accumulation. (See Washington case Geise v. Lee, 84 Wn.2d 866, 529 (1975)).