The bora is an extremely violent katabatic wind that descends from the interior plateaux and mountains of the Balkans (Slovenia, Croatia, Montenegro) toward the Adriatic Sea coast. It reaches gusts of 150-250 km/h in extreme cases, especially in the Gulf of Trieste and along the Dalmatian coast, where it is one of the most feared winds in the Mediterranean.
Formation mechanism
The bora forms when cold continental air accumulates on the Balkan plateaux, held back by the coastal mountains (Dinaric Alps). When the build-up is sufficient, the cold, dense air overflows the mountain ridges and plunges downslope under gravity. As it descends, the air compresses and warms adiabatically, but because it starts from such low temperatures (-10 to -20 °C on the plateaux), it still arrives at the coast as a bitterly cold and brutal wind.
Two types are distinguished: the anticyclonic bora (clear skies, extremely cold and dry air, the most common) and the cyclonic bora (associated with an Adriatic depression, with clouds, snow, and rain, even more dangerous for navigation). Both can last 1 to 5 days.
The effects on the Adriatic are devastating: extremely rough seas, impossible navigation, freezing of port structures, and coastal road closures due to gusts. It is analogous to the Spanish cierzo and the French mistral, all being topographically channelled winds. See also: katabatic wind.