  We present an original phenomenological model to describe the evolution of
galaxy number counts, morphologies, and spectral energy distributions across a
wide range of redshifts (0.2<z<15) and stellar masses [Log10 M/Msun >6]. Our
model follows observed mass and luminosity functions of both star-forming and
quiescent galaxies, and reproduces the redshift evolution of colors, sizes,
star-formation and chemical properties of the observed galaxy population.
Unlike other existing approaches, our model includes a self-consistent
treatment of stellar and photoionized gas emission and dust attenuation based
on the BEAGLE tool. The mock galaxy catalogs generated with our new model can
be used to simulate and optimize extragalactic surveys with future facilities
such as the James Webb Space Telescope (JWST), and to enable critical
assessments of analysis procedures, interpretation tools, and measurement
systematics for both photometric and spectroscopic data. As a first application
of this work, we make predictions for the upcoming JWST Advanced Deep
Extragalactic Survey (JADES), a joint program of the JWST/NIRCam and NIRSpec
Guaranteed Time Observations teams. We show that JADES will detect, with NIRCam
imaging, thousands of galaxies at z>6, and tens at z>10 at m_AB<30 (5-sigma)
within the 236 arcmin^2 of the survey. The JADES data will enable accurate
constraints on the evolution of the UV luminosity function at z>8, and resolve
the current debate about the rate of evolution of galaxies at z>8. Ready to use
mock catalogs and software to generate new realizations are publicly available
as the JAdes extraGalactic Ultradeep Artificial Realizations (JAGUAR) package.
