Astroclimatology of ESO Sites	ESO WIDE REVIEW M. Sarazin, April 2000, 3/10

Differential of the monthly fraction of photometric nights at Paranal and La Silla since the beginning of the VLT site survey. La Silla currently tops its 10-11 years cycle while Paranal experiences La Nina related weather degradation: the combination of both effects cancels the differences between the two sites.