The paper constructs modal structures that represent alternative developments of GRW systems. With these modal structures in hand, it shows that GRW probabilities can be read as graded modalities, that is, as numerically specified powers of a system to localize. The construction is intended as offering support for Dorato and Esfeld's (Stud Hist Philos Mod Phys 41(1):41–49, 2010) project of conceiving GRW theory as an ontology of powers.