From AMS Glossary
(Also spelled kosava, koschawa.) A cold, very squally wind, descending from the east or southeast in the region of the Danube "Iron Gate" through the Carpathians, continuing westward over Belgrade, thence spreading northward to the Rumanian and Hungarian borderlands and southward as far as Nish.
In winter it brings temperatures down to below -29°C and it is cool even in summer, when it is also dusty. It usually occurs with a depression over the Adriatic and high pressure over southern Russia, a frequent situation in winter. It is usually explained as a jet-effect wind through the Iron Gate, giving speeds well above the gradient wind, but J. Küttner (1940) regards it rather as a katabatic wind intermediate between foehn and bora. The kossava has a marked diurnal variation, with its maximum occurring between 5
Küttner, J. 1940. Der Kosava in Serbien. Meteor. Z. 57. 120–123.