  Y dwarfs are the coolest spectral class of brown dwarf. They have effective
temperatures less than 500 K, with the coolest detection as low as ~250 K.
Their spectra are shaped predominantly by gaseous water, methane, and ammonia.
At the warmer end of the Y dwarf temperature range, spectral signatures of
disequilibrium carbon monoxide have been observed. Cooler Y dwarfs could host
water clouds in their atmospheres. Since they make up the low-mass tail of the
star formation process, and are a valuable analogue to the atmospheres of giant
gaseous exoplanets in a temperature range that is difficult to observe,
understanding Y dwarf atmospheric compositions and processes will both deepen
our understanding of planet and star formation, and provide a stepping stone
towards characterizing cool exoplanets. JWST spectral observations are
anticipated to provide an unprecedented level of detail for these objects, and
yet published self-consistent model grids do not accurately replicate even the
existing HST and ground-based observations. In this work, we present a new
suite of 1-d radiative-convective equilibrium models to aid in the
characterization of Y dwarf atmospheres and spectra. We compute clear, cloudy,
equilibrium-chemistry and disequilibrium-chemistry models, providing a
comprehensive suite of models in support of the impending JWST era of
panchromatic Y dwarf characterization. Comparing these models against current
observations, we find that disequilibrium CH4-CO and NH3-N2 chemistry and the
presence of water clouds can bring models and observations into better, though
still not complete, agreement.
