  The forecast on a time scale of 1 or 2 hours is crucial for all kind of new
generation facilities (ELTs) instrumentation supported by the adaptive optics
that will be mainly operated in Service Mode. In a recent study (Masciadri et
al. 2020) we have showed that we can forecast the seeing and atmospheric
parameters at such short time scales using an autoregressive method achieving
unprecedented model accuracies with a substantial gain with respect to
forecasts performed the day before (i.e. on longer time scales) obtained with
an atmospheric mesoscale model. Equally we showed a gain with respect to the
method by persistence using simply real-time measurements in situ on the same
short time scale (1-2 hours). The auto-regressive method makes use of the
forecasts done with mesoscale atmospheric models and real-time measurements and
since 2019 has been implemented in the operational forecast system ALTA Center
supporting LBT observations. In this contribution we apply the same approach to
the VLT site extending the method to all the main astroclimatic parameters i.e.
the seeing, the wavefront coherence time, the isoplanatic angle and the ground
layer fraction. We prove that such a method offers unprecedented forecast
accuracies for all the astroclimatic parameters with clear gains with respect
to the prediction by persistence. Preliminary calculations indicate also better
accuracies than those obtained with the machine learning based approach using
in situ measurements. We will apply soon such a method in an operational
forecast system that we conceived for the VLT.

Instrumentation and Methods for Astrophysics