  We present a Python package, pwv_kpno, that provides models for the
atmospheric transmission due to precipitable water vapor (PWV) at user
specified sites. Using the package, ground-based photometric observations taken
between $3,000$ and $12,000$ $\AA$ can be corrected for atmospheric effects due
to PWV. Atmospheric transmission in the optical and near-infrared is highly
dependent on the PWV column density along the line of sight. By measuring the
delay of dual-band GPS signals through the atmosphere, the SuomiNet project
provides accurate PWV measurements for hundreds of locations around the world.
The pwv_kpno package uses published SuomiNet data in conjunction with MODTRAN
models to determine the modeled, time-dependent atmospheric transmission. A
dual-band GPS system was installed at Kitt Peak National Observatory (KPNO) in
the spring of 2015. Using measurements from this receiver we demonstrate that
we can successfully predict the PWV at KPNO from nearby dual-band GPS stations
on the surrounding desert floor. The pwv_kpno package can thus provide
atmospheric transmission functions for observations taken before the KPNO
receiver was installed. Using PWV measurements from the desert floor, we
correctly model PWV absorption features present in spectra taken at KPNO. We
also demonstrate how to configure the package for use at other observatories.
