Climatological characteristics of the Ora del Garda wind in the Alps

The Ora del Garda is a coupled lake and valley breeze regularly blowing from the northern shorelines of Lake Garda, in the Italian Alps, especially during warm-season clear-sky days. The climatological characteristics of this wind are investigated through the analysis of 10 years of observations collected at two representative surface weather stations - one on Lake Garda's shore and the other 30 km inland. Furthermore, the possible influences of the land-water temperature contrast and of the synoptic wind on the development and the propagation of the Ora del Garda are analysed. Lake-breeze days are identified by means of a set of objective criteria based on observations of solar radiation, wind speed and direction at the two stations. The analysis highlights that, on the lake's shoreline, the breeze develops on about 70% of the days in the warmest months, while it rarely occurs from October to February. Moreover, in the warmest months, the Ora del Garda reaches the inland weather station on about 80-90% of the days on which it blows on the lake's shore, after 3.5 h on average. It displays rather strong intensities, reaching average velocities of 5 m s(-1) and gusts of 10 m s(-1), respectively, in summer on the lake's shore and in spring at the inland weather station. No clear relationship is found between the land-water temperature contrast and the lake-breeze strength. On the other hand, synoptic winds are observed to affect significantly the development of the breeze. In particular, onshore synoptic winds are associated with stronger intensities at the lake's shore. Moreover, in these situations the Ora del Garda propagates faster and is detected earlier at the inland weather station.