  High-resolution spectra are unique indicators of three-dimensional processes
in exoplanetary atmospheres. For instance, in 2020, Ehrenreich et al. reported
transmission spectra from the ESPRESSO spectrograph yielding an anomalously
large Doppler blueshift from the ultra-hot Jupiter WASP-76b. Interpretations of
these observations invoke toy model depictions of gas-phase iron condensation
in lower-temperature regions of the planet's atmosphere. In this work, we
forward model the atmosphere of WASP-76b with double-gray general circulation
models (GCMs) and ray-striking radiative transfer to diagnose the planet's
high-resolution transmission spectrum. We confirm that a physical mechanism
driving strong east-west asymmetries across the terminator must exist to
reproduce large Doppler blueshifts in WASP-76b's transmission spectrum. We
identify low atmospheric drag and a deep radiative-convective boundary as
necessary components of our GCM to produce this asymmetry (the latter is
consistent with existing Spitzer phase curves). However, we cannot reproduce
either the magnitude or the time-dependence of the WASP-76b Doppler signature
with gas-phase iron condensation alone. Instead, we find that high-altitude,
optically thick clouds composed of $\rm Al_2O_3$, Fe, or $\rm Mg_2SiO_4$
provide reasonable fits to the Ehrenreich et al. observations -- with marginal
contributions from condensation. This fit is further improved by allowing a
small orbital eccentricity ($e \approx 0.017$), consistent with prior WASP-76b
orbital constraints. We additionally validate our forward-modeled spectra by
reproducing lines of nearly all species detected in WASP-76b by Tabernero et
al. 2021. Our procedure's success in diagnosing phase-resolved Doppler shifts
demonstrates the benefits of physical, self-consistent, three-dimensional
simulations in modeling high-resolution spectra of exoplanet atmospheres.
