  We introduce a class of modules over Kac-Moody superalgebras; we call these
modules snowflake. These modules are characterized by invariance property of
their characters with respect to a certain subgroup of the Weyl group. Examples
of snowflake modules appear as admissible modules in representation theory of
affine vertex algebras and in classification of bounded weight modules. Using
these modules we prove Arakawa's Theorem for the Lie superalgebra osp(1|2n).
