  We report the first discovery of the emergence of a high-velocity broad-line
outflow in a luminous quasar, J105400.40+034801.2 at redshift z ~ 2.1. The
outflow is evident in ultraviolet CIV and SiIV absorption lines with velocity
shifts v ~ 26,300 km/s and deblended widths FWHM ~ 4000 km/s. These features
are marginally strong and broad enough to be considered broad absorption lines
(BALs), but their large velocities exclude them from the standard BAL
definition. The outflow lines appeared between two observations in the years
2002.18 and 2006.96. A third observation in 2008.48 showed the lines becoming
~40% weaker and 10% to 15% narrower. There is no evidence for acceleration or
for any outflow gas at velocities <23,000 km/s. The lines appear to be
optically thick, with the absorber covering just 20% of the quasar continuum
source. This indicates a characteristic absorber size of ~4 x 10^15 cm, but
with a BAL-like total column density log N_H (cm^-2) > 21.2 and average space
density n_H > 2 x 10^5 cm^-3. We attribute the emergence of the outflow lines
to a substantial flow structure moving across our line of sight, possibly near
the ragged edge of the main BAL flow or possibly related to the onset of a BAL
evolutionary phase.
