  The 4.8 GHz lightcurves of the scintillating intra-day variable quasar
J1819+3845 during 2004-5 exhibit sharp structure, down to a time scale of 15
minutes, that was absent from lightcurves taken prior to this period and from
the 2006 lightcurves. Analysis of the lightcurve power spectra show that the
variations must be due to the emergence of new structure in the source. The
power spectra yield a scattering screen distance of 3.8 +/- 0.3 pc for a
best-fit v_ISS=59 +/- 0.5 km/s or 2.0 +/- 0.3 pc for the scintillation velocity
reported by Dennett-Thorpe & de Bruyn (2003). The turbulence is required to be
exceptionally turbulent, with C_N^2 > 0.7 Delta L_pc^{-1} m^{-20/3} for
scattering material of thickness Delta L_{pc} pc along the ray path. The 2004
power spectrum can be explained in terms of a double source with a component
separation 240 +/- 15 microas in 2004.
