  When neutrinos travel through matter with a periodic density profile, the
neutrino oscillation probability can be enhanced if certain conditions are
satisfied. In a two-neutrino framework, the condition for parametric resonance
is known. Herein, we consider the analogous parametric resonance condition
within the context of a full three-neutrino framework with two oscillation
scales. For energies in the range of hundreds of MeV to a few GeV, we find that
neutrino oscillation can be parametrically enhanced if two approximate
relations are satisfied. The first is similar to the two-neutrino parametric
resonance condition while the second involves the other oscillation scale.
Treating the Earth's density as piecewise constant, we show that oscillations
in this energy range can be enhanced between two- and threefold.
