  Optical turbulence affects significantly the quality of ground-based
astronomical observations. An accurate and reliable forecast of optical
turbulence can help to optimise the scheduling of the science observations and
to improve both the quality of the data and the scientific productivity of the
observatory. However, forecasts of the turbulence to a level of accuracy that
is useful in the operations of large observatories are notoriously difficult to
obtain. Several routes have been investigated, from detailed physical modelling
of the atmosphere to empirical data-driven approaches. Here, we present an
empirical approach exploiting spatial diversity and based on simultaneous
measurements between two nearby sites, Cerro Paranal, host of the Very Large
Telescope (VLT), and Cerro Armazones, future host of the Extremely Large
Telescope (ELT) in Chile. We study the correlation between the high-altitude
turbulence as measured between those two sites. This is part of the on-going
efforts initiated by the European Southern Observatory (ESO), to obtain
short-term forecasts of the turbulence to facilitate the operations of the VLT
and prepare the ELT mode of operations.
