The potential of numerical weather prediction to supply a useful support to
flexible scheduling of astronomical observations is investigated. We appli
ed some common tools presently used in numerical meteorology at regional sc
ale in order to evaluate the ability to forecast local meteorological condi
tions (cloud cover, air temperature and wind speed) at Cerro Paranal and Ce
rro La Silla in Chile, where telescopes of ESO (the European Southern Obser
vatory) are sited. The first part of this paper is devoted to evaluating th
e accuracy of analysis and forecasts of the ECMWF (European Center for Medi
um-range Weather Forecast) general circulation model for ESO needs. With th
is aim, analysis and 24-48 hour forecasts from ECMWF are systematically com
pared with observations at the ground meteorological stations of Paranal an
d La Silla, and with vertical profiles of radiosounding launches at Antofag
asta and Quintero. The second part of this paper is aimed at improving the
ECMWF forecasts at telescope sites by means of Kalman filter statistical po
st-processing and meteorological limited area modeling. Encouraging results
are obtained concerning temperature, whereas much less satisfactory result
s are obtained for wind field and cloud cover. The most critical aspects of
atmospheric dynamics affecting the local forecast are discussed within the
limits of available information.