The cold bora wind affects the entire Istrian Peninsula. It is a katabatic wind, like the Santa Ana in California and the Mistral in the Mediterranean. Katabatic winds are downdrafts that carry winds from higher to lower elevations. In this instance, the heavier (colder, denser) air over the Alps is carried by gravity down to the warmer, lighter air over the Adriatic.
Above: the mean streets of downtown Trieste, Italy, during the occasion of a bora wind.
The bora, which occurs most ofter in winter, affects Croatia, Slovenia and Italy. It blows in gusts. On March 15, 2006, a gust was clocked at a bridge in Croatia at more than 155 MPH (235 KPH). The bora can last for several days at a time and usually occurs several times each year (on average about 40 days a year). Coastal towns are built densely with narrow streets, in part because of the wind. Buildings in several towns and villages in Slovenia and the Italian province of Trieste have stones on their roofs to prevent the roof tiles from being blown off. It is not uncommon to see entire rows of motorcycles and mopeds blown over onto their sides in Trieste.
Chains and ropes are occasionally stretched along the sidewalks in downtown Trieste to facilitate pedestrian traffic; there is a danger of being blown off one's feet and into traffic! (click to enlarge photo)
Trivia: The Volkwagen models Bora, Sirocco and Passat are all named after winds, with the insinuation that their cars "move like the wind."