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Thebora is a northerly to north-easterlykatabatic wind in areas near theAdriatic Sea. Similar nomenclature is used for north-eastern winds in other littoral areas of easternMediterranean andBlack Sea basins.
It is known inGreek asμπόρα (mpóra, pronouncedbora) and Italian asbora. In English, the namebora is used.[1][2] TheSerbo-Croatian namebura andSloveneburja are not etymologically related tobora; they derive from Common Slavicburja 'storm' (from the verb*burĭti), and the meaning 'bora' developed later.[3]
The same root asbora is found in the name of theGreek mythological figure ofBoreas (Βορέας), and the Modern Greek word for the north windβοράς. Historical linguists speculate that the name may derive from aProto-Indo-European root *gworhx- 'mountain', which gave rise to Slavicgora and Sanskritgiri-, both 'mountain'.[4]
The changeable bora can often be felt all overAdriatic Croatia, theMontenegrin Littoral, theSlovenian Littoral,Trieste, and the rest of the Adriatic east coast. It blows in gusts. The bora is most common during the winter. It affects coastal areas and it weakens into the open sea.
It blows hardest when a polar high-pressure area sits over the snow-covered mountains of the interior plateau behind theDinaric coastal mountain range and a calm low-pressure area lies further south over the warmerAdriatic.[5] As the air grows even colder and thus denser at night, the bora increases. Its initial temperature is so low that even with the warming occasioned by its descent it reaches the lowlands as a cold wind.[6]
The wind takes two different traditional names in areas of Italy and Croatia depending on associated meteorological conditions: the "light bora" (Italian:bora chiara) is a bora in the presence ofanticyclone clear skies, whereascyclone clouds gathering on the hilltops and moving towards the seaside with rain or snow characterize the "dark bora" (Italian:bora scura,Croatian:škura bura).[7]
The area where some of the strongest bora winds occur is theVelebit mountain range inCroatia. This seaside mountain chain, spanning 145 km, represents a huge weather and climatic divide between the sharpcontinental climate of the interior, characterized by significant day/night temperature differences throughout the year, and the Adriatic coast, with aMediterranean climate. The bora occurs because these two divided weather systems meet and tend to equalize over the mountain range.
Sailing during the bora can be challenging and it requires caution, regarding readiness of both the boat and its crew. Short, high waves with white crests are its characteristics, making the navigation difficult. The small drops formed by the wind create a so-called "sea smoke" that reduces the visibility significantly. Experienced seamen have a proverb: "When the bora sails, you don't!"[8] Sailing can be extremely dangerous for an inexperienced navigator in theVelebit Channel because the wind can start suddenly on a clear and calm day and result in major problems, frequently also affecting road traffic.
Near the towns ofSenj,Stara Novalja,Karlobag and the southern portal of theSveti Rok Tunnel in Croatia, it can reach speeds of up to 220 km/h. On 21 December 1998 the speed of a gust on theMaslenica Bridge (north ofZadar) was measured at a record speed of 69 m/s or 248 km/h.[9][10] Wind shields were installed on that part of the highway.[11] During 22 to 25 December 2003 onA1 highway near Sveti Rok Tunnel a reading measured the speed of 304 km/h, but this is not considered an official record because the instruments were not calibrated for such speed.[7]
Incidents where the Adriatic Sea becomes covered in ice during a bura storm have been recorded in 1956 in Senj and 1963 inMakarska.[12] The maximum duration of constant intense bura winds has been measured at 67–68 hours inDalmatia.[12] In February 2012, during theearly 2012 European cold wave, the shoreline in Senj froze and snow piled up after a 150 km/h bora plummeted the temperature to −14 °C, with 7 meter-high waves. The bora ripped the trees from the soil and destroyed roofs of houses.[13] On the island of Pag, the Bora threw fish out of the sea. In many Croatian coastal cities, fresh water froze inside the pipes.[14]
The wind is also an integral feature of Slovenia'sVipava Valley and, to a lesser extent, theKarst Plateau (known asCarso in Italian), an area of limestone heights over theGulf of Trieste stretching towards theIstrian peninsula. Because the region separates the lower Adriatic coast from theJulian Alps range, extreme bora winds often occur there. They have influenced the region's traditional lifestyle and architecture. Towns on the coast, where the bora frequently occurs, are built densely with narrow streets in part because of the wind. Buildings in several towns and villages inSlovenia and theProvince of Trieste (Italy) have stones on their roofs to prevent the roof tiles from being blown off. Chains and ropes are occasionally stretched along the sidewalks in downtownTrieste, Italy, to facilitate pedestrian traffic – gusts in the city are usually above 120 km/h reaching to maxima of near 200 km/h. A strong bora will often be reported on Italian television news. Slovenian towns where the strongest bora occurs areAjdovščina,Vipava and, to a lesser extent,Nova Gorica. In Slovenia, the most affected section is usually the upper part of the Vipava Valley, stretching from Ajdovščina toPodnanos, where the speed of the wind can exceed 200 km/h.[15]
Strong bora winds also occur in theTsemes Bay of theBlack Sea near the Russian port ofNovorossiysk, where they are known asnordost 'northeastern'.[16] They can reach speeds of up to 220 km/h.
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