Croatia’s climate is determined by its position in the northern mid-latitudes and the corresponding weather processes on a large and medium scale. The most important climate modifiers over Croatia are the Adriatic and the Mediterranean, the Dinarides’ orography with their form, altitude and position relative to the prevailing air flow, the openness of the north-eastern parts to the Pannonian plain, and the diversity of vegetation. Therefore the following three main types of regions - with continental, mountain and maritime climate, prevail in Croatia.
The most common are Köppen and Thornthwait climate classisfications. Details of Croatia’s climate could be found in Klimatskom atlasu Hrvatske / Climate atlas of Croatia 1961-1990., 1971-2000.
Continental Croatia has a temperate continental climate and throughout the whole year it is in a circulation zone of mid-latitudes, where the atmospheric conditions are very variable. They are characterised by a diversity of weather situations with frequent and intense exchanges during the year. These are caused by moving systems of low or high air pressure, often resembling vortices hundreds and thousands of kilometres in diameter. The climate of continental Croatia is modified by the maritime influence of the Mediterranean, which is stronger in the area south of the Sava River than in the north, and which weakens towards the east. The next local climate modifier is orography which, for example, facilitates the intensification of short-term heavy precipitation on the windward side of the orographic obstacle or the appearance of precipitation shadow on the leeward side. Weather characteristics differ between seasons.
During the cold part of the year, stationary anticyclonic weather types, with foggy weather or low clouds and a very gentle air flow, are prevalent. Such conditions are favourable for frost occurrence.
In spring, fast-moving cyclonic weather types (cyclone and trough) are characteristic, resulting in frequent and sudden weather changes, from rainy to dry periods, from calm to windy, from colder to warmer. In April, there are usually about ten successive days with a moderate, even strong cold northern wind at the front side of the meridional anticyclone stretching from Scandinavia to Central and even Southern Europe.
In summer, the zero pressure gradient fields and a cooling night breeze blowing down mountain slopes are interrupted by cold fronts passing through. They bring in fresh air from the Atlantic, with very strong air mixing, increased wind, thunder and showers from dense clouds with vertical development. This unstable atmosphere stratification and convective clouds usually stay for a day or two after the cold air outbreak, until the new air mass is warmed by the land surface.
In autumn, periods of calm anticyclonic weather are very common, but there are also rainy days as cyclones pass over Croatian territory. Calm weather in early autumn is characterised by warm and sunny days and fresh nights with heavy dew and low fog patches over streams and rivers, which dissipate quickly by the morning. In late autumn, calm weather is cold, foggy and gloomy; in open plains there is a short period of sunshine through fog around noon. On mountain peaks, however, the weather is sunny throughout the whole day.
At higher altitudes, in the mountainous districts of Gorski kotar, Lika and the Dinaric Alps, there is a mountain climate that differs from the wider area primarily by its air temperature and snow regime, characterized with lower temperatures and more abundant snow and longer-lasting snow cover.
The Croatian Littoral is also in a circulation area of mid-latitudes with frequent and intense weather changes most of the year. In summer, however, this area comes under the influence of the subtropical zone, as a result of the influence of the Azorean anticyclone, which prevents cold air outbreaks to the Adriatic. One of the most important climate modifiers in this area is the sea, so the climate can be referred to as maritime.
With the direct influence of the Northern Adriatic cyclogenetic effect, the climate in this area is extremely modified by the highly developed orography of Gorski kotar and the Dinarides. Cyclonic activity, typical of winter, early spring and late autumn, is equally significant for the cloud and precipitation regime of the coast and the hinterland. In the cold period, cyclones mostly do not pass from the Adriatic to the mainland.
In summer, on the Adriatic, stationary clear weather prevails in the zero pressure gradient field of about 1015 hPa. Due to the general pressure gradient in the Mediterranean and the position of the Adriatic, there are north-western winds (etesians) in the open sea, a gentle wind in the Northern Adriatic, moderate wind in the Middle Adriatic, and, occasionally, strong wind closer to the Strait of Otranto. At the same time, local daily periodic circulation is developed on the larger islands and the coast, due to the unequal warming (and cooling) tendencies of the sea and the land, as well as of the hills and the surrounding valleys. Its most important characteristics are a regular daily wind from sea to land and, at night, wind blowing from land and down hill slopes towards the sea. All this enables a strong turbulent exchange of air characteristics, the establishment of a homogeneous spatial distribution of meteorological parameters and the mitigation of extremes.
During the cold part of the year (and at night), in calm weather, turbulence is gentle, so local conditions are dominant, and, therefore, there are great differences in the values, courses and spatial distribution of meteorological parameters at adjacent stations. On the other hand, the strong winds, bura and jugo, are more frequent and stronger in the cold part of the year, although the intensity of the summer bura can also create problems in road and maritime traffic.
During the cold part of the year, especially in winter, the typical Northern Adriatic wind is bura. It blows from the north-eastern quadrant and is known for its gustiness, high speed and duration. Bura is not formed only on the edge of winter inland anticyclones, which stretch to the coastal mountains, but also when cold air from the ground layer descends from the mountains into the warmer area above the sea. Bura is the strongest when the general pressure gradient stimulates an air flow over the mountain ridge. Then it causes great damage, and, as a wind blowing to the open sea and dispersing surface wave tips, it reaches remote distances from the shore. The average wind speed during bura is several tens of kilometres per hour, but the speed of individual wind gusts is much higher. The highest speed recorded was 69 m/s, i.e. 248 km/h at the Maslenica Bridge station on 21 December 1998. Bura is the prevalent and the strongest wind in the sub-Velebit area and it weakens as it moves away from the shore. It is also a dominant wind in the coastal area of Istria, although it is weaker and it is not present in the hinterland of the peninsula. On the Middle and Southern Adriatic, where the well known bura locations are Kliška vrata, Vrulje, Makarska Littoral and Rijeka Dubrovačka, bura is usually less intense and less frequent than on the Northern Adriatic. Jugo (sirocco) is a more intense and frequent wind in these areas.
Jugo is a steady and strong wind which blows evenly with a speed similar to the bura average speed, being the highest in the conveniently positioned channels between the islands and the coastland. The wind occurs in the air flow from the southern quadrant and often has a southward direction into the open sea, while the coastal mountains turn it to SE. Jugo is more intense and frequent on the Middle and Southern Adriatic than on the Northern Adriatic.
More about climate
Köppen climate classification
According to the Köppen climate classification, where the mean annual temperature course and precipitation amount are considered, most of Croatia has a temperate rainy climate with an average monthly temperature higher than -3 °C and lower than 18 °C (symbol C) in the coldest month. Only the highest mountain areas (>1200 m asl) have a snow-forest climate with an average temperature lower than -3 °C in the coldest month (symbol D). Inland, the warmest month of the year has an average temperature lower than 22 °C (symbol b), in the coastal area higher than 22 °C (symbol a), and more than four months within one year have a monthly average temperature higher than 10 °C. The lowland, continental part of Croatia has a Cfwbx” climate. With the previously mentioned temperature characteristics (symbols C and b), there are no extremely dry months during the year, and the month with the smallest amount of precipitation is in the cold part of the year (fw). In the annual course of precipitation there are two maxima (x”). The mountainous area of Lika and Gorski kotar, and the higher parts of Istria belong to the Cfsbx” climate class, while the mountain peaks (higher than 1200 m asl) belong to the Dfsbx” class. In these areas there are no dry periods, the highest monthly amount of precipitation is in the cold part of the year (fs), and the winter rainy period is divided into the autumn-winter and the spring maximum (x”). On the islands and in the coastal area of the Middle and Southern Adriatic, there is a prevalent olive climate (Csa), which means that the dry period is in the warm part of the year, and the driest month has even less than 40 mm of precipitation, less than a third of the amount in the rainiest month in the cold part of the year (symbol s). There are also two precipitation maxima (x”) in the larger part of the area.
Thornthwaite climate classification
According to the Thornthwaite climate classification, based on the relation between the amount of water necessary for potential evapotranspiration and water obtained from precipitation, there are five types of climate, from perhumid to arid. Croatia has perhumid, humid and subhumid climates. In the largest part of lowland, continental Croatia there is a prevalent humid climate, and a subhumid climate only in eastern Slavonia. The perhumid climate prevails in the highlands. In coastal Croatia, there are perhumid, humid and subhumid climates. In the Northern and Middle Adriatic a humid climate prevails, whereat inland Istria, Kvarner Bay and hinterland of Dalmatia are more humid than the Istrian coast and the Middle Adriatic. In the Kvarner Bay, beside the cyclogenetic effect, the mountainous hinterland generates high amounts of precipitation, because of its orographic effect that intensifies precipitation, which is specially manifested in the wider region of Rijeka. Therefore, according to the Thornthwaite index values, Rijeka has a perhumid climate, similar to that which is prevalent in the highland part of Croatia. In some parts of the Middle Adriatic and on the Southern Adriatic, subhumid conditions prevail. However, the southernmost parts, around Dubrovnik, towards the hilly hinterland, have a humid climate because of high precipitation amounts.