  Theories of high energy radiation production in quasar jets can be verified
by studies of both time-averaged spectra and variability patterns. While the
former has been explored extensively, the latter is in its infancy. In this
paper, we study the production of short-term flares in the shock-in-jet model.
We examine how the flares' profiles depend on such parameters as
shock/dissipation lifetime, electron-injection time profile, adiabaticity, and
half-opening angle of the jet. In particular, we demonstrate the large
difference between flare profiles produced in the radiative and adiabatic
regimes. We apply our model to the $\sim$day timescale flares observed in
optically violently variable (OVV) quasars, checking whether the
external-radiation-Compton (ERC) model for $\gamma$-ray flares at energies $>
30$ MeV (EGRET range) can be reconciled with the flares observed at lower
energies. Specifically, we show that the strict correlation between X-ray and
$\gamma$-ray flares strongly supports the dominance of the synchrotron
self-Compton mechanism in the X-ray band. We also derive conditions that must
be satisfied by the ERC model in order to explain a lag of the $\gamma$-ray
peak behind the optical one, as claimed to be observed in PKS 1406-076.
Finally, we predict that in ERC models where the MeV peak is related to the
break in electron distribution due to inefficient cooling of electrons below a
certain energy, the flares should decay significantly more slowly in the soft
$\gamma$-ray band than at energies greater than 30 MeV.
