  As part of a program to investigate jet flow conditions during GeV gamma-ray
flares detected by Fermi, we are using UMRAO multi-frequency, centimeter-band
total flux density and linear polarization monitoring observations to constrain
radiative transfer models incorporating propagating shocks orientated at an
arbitrary angle to the flow direction. We describe the characteristics of the
model, illustrate how the data are used to constrain the models, and present
results for three program sources with diverse characteristics: PKS 0420-01, OJ
287, and 1156+295. The modeling of the observed spectral behavior yields
information on the sense, strength and orientation of the shocks producing the
radio-band flaring; on the energy distribution of the radiating particles; and
on the observer's viewing angle with respect to the jet independent of VLBI
data. We present evidence that, while a random component dominates the jet
magnetic field, a distinguishing feature of those radio events with an
associated gamma-ray flare is the presence of a weak but non-negligible ordered
magnetic field component along the jet axis.
