  Recent transit surveys have discovered thousands of planetary candidates with
directly measured radii, but only a small fraction have measured masses.
Planetary mass is crucial in assessing the feasibility of numerous
observational signatures, such as radial velocities (RVs), atmospheres, moons
and rings. In the absence of a direct measurement, a data-driven, probabilistic
forecast enables observational planning and so here we compute posterior
distributions for the forecasted mass of approximately seven thousand Kepler
Objects of Interest (KOIs). Our forecasts reveal that the predicted RV
amplitudes of Neptunian planets are relatively consistent, as a result of
transit survey detection bias, hovering around the few m/s level. We find that
mass forecasts are unlikely to improve through more precise planetary radii,
with the error budget presently dominated by the intrinsic model uncertainty.
Our forecasts identify a couple of dozen KOIs near the Terran-Neptunian divide
with particularly large RV semi-amplitudes which could be promising targets to
follow-up, particularly in the near-IR. With several more transit surveys
planned in the near-future, the need to quickly forecast observational
signatures is likely to grow and the work here provides a template example of
such calculations.
