  We study the prospects for the Large Synoptic Survey Telescope (LSST) to find
new dwarf spheroidal galaxies in the Milky Way. Adopting models of Milky-Way
halo substructure and phenomenological prescriptions connecting subhalos and
satellite galaxies, we obtain surface brightness distributions of $V$-band
magnitude that lead us to predict that LSST will discover tens to hundreds of
dwarf spheroidal galaxies above its sensitivity. The soon-to-be-discovered
dwarfs will be interesting targets for indirect searches of dark matter
annihilation yields. We forecast the distribution function of gamma-ray
emission from dark matter annihilation in these objects, and discuss the
detectability of these signals at both Fermi Large Area Telescope (LAT) and
Cherenkov Telescope Array (CTA). By combining information from the predicted
dwarf galaxies, we obtain an expected sensitivity to the annihilation cross
section $\langle \sigma v \rangle$ of $10^{-26}$ cm$^3$ s$^{-1}$ (for dark
matter particles of mass 10 GeV with Fermi-LAT) and $5\times 10^{-24}$ cm$^3$
s$^{-1}$ (for dark matter particles of mass 500 GeV with CTA). We find that the
current uncertainties in the mass measurement of the Milky-Way halo are
relatively minor compared with the Poisson errors associated to drawing the
most promising dwarfs from the underlying flux distribution.
