  Brown dwarfs are essential targets for understanding planetary and
sub-stellar atmospheres across a wide range of thermal and chemical conditions.
As surveys continue to probe ever deeper, and as observing capabilities
continue to improve, the number of known Y dwarfs -- the coldest class of
sub-stellar objects, with effective temperatures below about 600 K -- is
rapidly growing. Critically, this class of ultra-cool objects has atmospheric
conditions that overlap with Solar System worlds and, as a result, tools and
ideas developed from studying Earth, Jupiter, Saturn and other nearby worlds
are well-suited for application to sub-stellar atmospheres. To that end, we
developed a one-dimensional (vertical) atmospheric structure model for
ultra-cool objects that includes moist adiabatic convection, as this is an
important process for many Solar System planets. Application of this model
across a range of effective temperatures (350, 300, 250, 200 K), metallicities
([M/H] of 0.0, 0.5, 0.7, 1.5), and gravities (log $g$ of 4.0, 4.5, 4.7, 5.0)
demonstrates strong impacts of water latent heat release on simulated
temperature-pressure profiles. At the highest metallicities, water vapor mixing
ratios reach an Earth-like 3%, with associated major alterations to the thermal
structure in the atmospheric regions where water condenses. Spectroscopic and
photometric signatures of metallicity and moist convection should be readily
detectable at near- and mid-infrared wavelengths, especially with James Webb
Space Telescope observations, and can help indicate the formation history of an
object.
