  The isovector axial form factor of the nucleon plays a key role in
interpreting data from long-baseline neutrino oscillation experiments. We
present a lattice QCD calculation of this form factor, introducing a new method
to directly extract its z-expansion from lattice correlators. Our final
parameterization of the form factor, which extends up to spacelike virtualities
of 0.7 GeV^2 with fully quantified uncertainties, agrees with previous lattice
calculations but is significantly less steep than neutrino-deuterium scattering
data suggests.
