Condensate clouds should pervade the atmospheres of brown dwarfs and exoplanets, dictating the energy balance of these substellar objects and controlling their photometric and spectroscopic properties. Yet physical understanding of these clouds has largely been limited to coarse phenomenology: clouds are difficult to model and even more difficult to observe, owing to the absence of prominent spectral features and the intrinsic low luminosity of ultracool LT dwarfs. Here we present high resolution near-IR echelle spectra from IGRINS taken contemporaneously with TESS Sector 36 to quantify brown dwarf cloud modulation of Luhman 16AB, an exemplar L-T transition binary residing 2 pc from the Sun. The Sector 10, 36, and 37 lightcurves show conspicuous 10% peak-to-valley modulations arising from longitudinal asymmetries of cloud coverage, with rich harmonics suggestive of surface structures. The four epochs of IGRINS spectra sample both high and low states of cloud coverage of the B component, exhibiting wide agreement with custom cloudy synthetic grid models. We animate conceivable dynamic surface structures consistent with these two precision datasets.