  The Planck On-Fligh Forecaster (POFF) is a tool to predict when a position in
the sky will be within a selected angular distance from any receiver direction
of the Planck satellite according to its pre-programmed observational strategy.
This tool has been developed in the framework of the Planck LFI Core Team
activities, but it is now used by the whole collaboration. In this paper we
will describe the tool and its applications to plan observations with other
instruments of point sources which are expected to enhance the possibilities of
scientific exploitation of the Planck satellite data, once they will be
publicly available. Collecting simultaneous multi-frequency data, like those
that can be planned with the POFF, will help, on one hand, to investigate
variability of point sources and, on the other, to reconstruct point source
spectral energy distributions on wide frequency ranges minimizing the effects
due to source variability. POFF is a combination of IDL routines which combine
the publicly available information about the Planck scanning strategy and focal
plane shape in order to identify if a given (list of) position(s) can be
observable by the satellite at a given frequency and/or by selected receivers
in a given time range. The output can be displayed with the desired time
resolution and selecting among various sorting options. The code is not a
Planck product, but it has been validated within the Planck LFI pipeline. The
code format and the large number of options make it flexible and suitable for
many applications, allowing to get results quickly. POFF is currently
successfully used to plan activities within the Planck collaboration, including
observations with several ground-based facilities, and it is distributed
outside it.
