The Collaborative International Dictionary of English v.0.48:

Variably \Va"ri*a*bly\, adv.
   In a variable manner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

variably
    adv 1: with variation; in a variable manner or to a variable
           degree; "it will be variably cloudy"

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "variably":
   at irregular intervals, at random, back and forth, brokenly,
   by catches, by fits, by jerks, by snatches, capriciously,
   changeably, desultorily, disconnectedly, discontinuously,
   eccentrically, erratically, fitfully, haltingly, in and out,
   in snatches, in spots, inconstantly, intermittently, irregularly,
   jerkily, lurchingly, nonuniformly, off and on, on and off,
   patchily, roughly, round and round, spasmodically, sporadically,
   spottily, to and fro, uncertainly, unevenly, unmethodically,
   unpredictably, unrhythmically, unsteadfastly, unsteadily,
   unsystematically, waveringly, whimsically, wobblingly