  We have used single-dish centimeter-band, multi-frequency linear polarization
and total flux density monitoring observations obtained by UMRAO at 14.5, 8,
and 4.8 GHz during gamma-ray flaring to constrain propagating shock-in-jet
models; this procedure allows us to probe jet conditions at or near the
presumed parsec-scale gamma-ray emission site within the relativistic jet.
Results are presented for the blazar 0420-014 during the gamma-ray flare
detected by the LAT which peaked in late January 2010. Our work identifies the
passage of three forward-moving transverse shocks during the radio-band
flaring, a shock Lorentz factor of 12, and an observer's viewing angle of 2
degrees and sets limits on the energy distribution of the radiating particles.
