  Using the Feynman diagram techniques, we derive the finite-temperature
conductivity and magnetoconductivity formulas from the quantum interference and
electron-electron interaction, for a three-dimensional disordered Weyl
semimetal. For a single valley of Weyl fermions, we find that the
magnetoconductivity is negative and proportional to the square root of magnetic
field at low temperatures, as a result of the weak antilocalization. By
including the contributions from the weak antilocalization, Berry curvature
correction, and Lorentz force, we compare the calculated magnetoconductivity
with a recent experiment. The weak antilocalization always dominates the
magnetoconductivity near zero field, thus gives one of the transport signatures
for Weyl semimetals. In the presence of strong intervalley scattering and
correlations, we expect a crossover from the weak antilocalization to weak
localization. In addition, we find that the interplay of electron-electron
interaction and disorder scattering always dominates the conductivity at low
temperatures and leads to a tendency to localization. Finally, we present a
systematic comparison of the transport properties of single-valley Weyl
fermions, 2D massless Dirac fermions, and 3D conventional electrons.
