MONTHLY BULLETIN FOR SERBIA

DECEMBER 2017

Belgrade, the 5th of January 2018

Division for Climate Monitoring and Climate Forecast

Department of National Center for Climate Change, Climate Model Development and Disaster

Risk Assessment

web: http://www.hidmet.gov.rs

mail: office@hidmet.gov.rs

Republic Hydrometeorological Service of Serbia

Kneza Viseslava 66

11000 Belgrade

Republic of Serbia

Warm and very warm December in most of the country, 4th warmest for Loznica. Two heat waves were recorded. Extremely rainy in south of the country, wettest December since the records began in Leskovac. MMS Kursumlija and Dimitrovgrad observed record-breaking daily precipitation sums.

Overview of the synoptic situation*

Frequent meridional deformation and great wave amplitudes, influence of the cyclone from northwest and Mediterranean, Alternation of the period characterized by warm and cold weather conditions, as well as period with precipitation and dry condition. At the beginning of the month, the Balkans was under the prevalence of the front side of the spatial and developed cyclone and upper air trough emanating from the western Europe and western Mediterranean, that is south-westerly upper air circulation. The series of wet air waves in the circulation and the gradual drop of geopotential brought shift in the weather. At first, it was rainy, with considerable sums being registered in south, southwest and southeast. The passage of the upper air axis and advection of the cold air brought snow the next day in most places in north parts of the country. In the lowland, snow cover was formed, and on the mountains there was sever wind.

The period between 6 and 16 December was marked by warmer and warm period for this time of the year with two cold incursions: between 9 and 10 as well as from 13 to 14 December. Namely, this period was characterized was by the developed cyclone in north and northwest of the continent, deepening of the upper air trough across the western Mediterranean and occasional deformation in southwestern upper air circulation and passage of the ground cyclone across the Balkans. Highest precipitation sums were recorded in west and southeast of the country.

In the period from 16 to 23 December it was considerably colder. Cyclone from northwest, at first front side of the trough, as well as closure of the upper air cyclone circulation took place as of December 20 above the Balkans. At first, the weather was rainy, and then cold and cloudy with moderate western and north-westerly wind.

In the period from 24 to 28 December, sunny and changeably cloudy weather was under the prevalence of a ridge, subsequently by south-westerly, upper air circulation and incursion of the warmer air. Deformation in south-westerly upper air circulation brought intermittent patches of rain in the west and south on December 28, and as of December 29 and 30, further temperature drop, colder and cloudy weather with light precipitation. The last day of the year was marked by re-establishing of the south-westerly upper air circulation in the ground with anticyclone and clearing along with the rise in the temperature.

• Division for aviation meteorology forecast

Air temperature

Mean monthly air temperature

Mean December air temperature ranged from -4.0ºС at Kopaonik to 5.4 ºС in Loznica (Figure 1).

Departure of the mean monthly air temperature from the normal1 for the 1981–2010 base period ranged from -0.6ºС at Kopaonik to 3.2ºС in Loznica (Figure 2).

Based on the percentile method2, mean air temperature in December was in the following categories: warm and very warm in most of Serbia, extremely warm in Loznica, and normal category on Zlatibor, Kopaonik, Sjenica and Vranje (Figure 3).

1 Term normal refers to climatological standard normal, that is, the average value of a particular climate element, calculated for the period from January 1, 1981 to December 31, 2010 2 n- nth percentile of a variable refers to the value of the observed variable below which there is n percent of data previously arranged in an ascending order

Figure 2. Spatial distribution of mean monthly air temperature anomaly (ºC) during December 2017

Figure 1. Spatial distribution of mean monthly air temperature (ºC) during December 2017

Based on the percentile method, mean daily air temperature in Belgrade was in the categories of very warm and warm most of December, whereas at the beginning of the second decade, it was extremely warm. At the beginning and end of the second decade, and at the end of month it was in the normal category (Figure 4).

Figure 3. Spatial distribution of the mean monthly air temperature using percentile method during December 2017

Figure 4. Monthly course of the mean daily air temperature in Belgrade in December 2017 December 2017 was the fourth warmest December for Loznica in the 1952-2017 period (Figure 5).

Figure 5. 15 years ranked by the highest mean December air temperature for Loznica for the 1952 – 2017 period

Maximum air temperature Mean maximum air temperature in December ranged from -1.1ºС at Kopaonik to 10.0ºС in Loznica.

Based on the percentile method, mean maximum monthly air temperature was in the following categories: very warm and warm in most of country, extremely warm in Zajecar and Negotin, normal in Crni Vrh, Zlatibor, Sjenica and Leskovac, and cold at Kopaonik.

The highest maximum daily air temperature of 21.1ºС was measured in Valjevo on December 12.

In December 2017, Serbia observed two heat waves3. The first heat wave was recorded between December 11-16 in Novi Sad and Loznica, and between December 12-16 in Nis. The second heat wave, lasting from December 24-28, was observed in most of Vojvodina, Loznica, Veliko Gradiste, Smederevska Palanka and Kragujevac.

Table 1. Heat Waves in Serbia during December 2017

3 Heat wave, according to the percentile method, is a period during which maximum daily air temperature is in the warm and very warm categories for 5 days or longer

The majority of the main meteorological stations registered ice days4. In the lowland, one ice days was observed in Kikinda, Banatski Karlovac, Pozega, Cuprija, Krusevac, Kursumlija and Leskovac, 2 days in Vranje, and 4 days in Dimitrovgrad. On the mountains, the number of ice days ranged from 7 in Sjenica to 16 days at Kopaonik.

Minimum air temperature Mean minimum air temperature in December ranged from -6.8ºС at Kopaonik to 2.1ºС in Belgrade.

Based on the percentile method, mean minimum monthly air temperature was in the following categories: warm in most of Serbia, very warm in Loznica, Valjevo and Kursumlija, and normal category in Veliko Gradiste, as well as parts of southern and southwestern Serbia.

The lowest minimum daily air temperature of -16.9ºС was measured in Sjenica on December 22.

Entire country experienced frost days5. The number of frost days in lowland ranged from 9 in Belgrade to 22 days in Pozega, and on the mountains from 24 at Crni Vrh to 31 days at Kopaonik. At most meteorological stations, the number of frost days was 1 to 6 days below the December average.

Days with severe frost6 were registered at Kopaonik and Sjenica, total of 10 and 5 days, respectively.

Figure 6 depicts the monthly course of the mean, maximum and minimum daily air temperature in Belgrade in December.

4 Ice day is defined as the day with maximum daily air temperature below 0°С 5 Frost day is defined as the day with minimum air temperature lower than 0°С 6 Day with severe frost is defined as the day with the minimum air temperature below -10°С

Figure 6. Monthly course of mean, maximum and minimum daily air temperature

PRECIPITATION

The registered amount of precipitation in December ranged from 43.1 mm in Banatski Karlovac to 142.3 mm in Nis (Figure 7).

Precipitation totals relative to the normal for the 1981-2010 base period ranged from 79% in Belgrade to 276% in Nis (Figure 8).

Based on the percentile method, precipitation sums were in the following categories: normal in most of Serbia, extremely rainy in southern parts of the country and Cuprija, very rainy in Sjenica and Zajecar, and rainy category in parts of western, eastern and central Serbia (Figure 9).

Figure 9. Monthly precipitation sums according to the percentile method

Figure 7. Spatial distribution of the monthly precipitation sums (mm)

Figure 8. Spatial distribution of the monthly precipitation sums in the percentages of normal for the 1981–2010 base period

December 2017 ranks as the 10th wettest December for Serbia in the 1951-2017 period (Figure 10). It was the wettest on record for Leskovac (Figure 11), the second wettest for Kursumlija and Nis (Figure 12 and 13), and the third wettest for Sjenica, Cuprija, Dimitrovgrad and Vranje.

Figure 10. Rank of the wettest and driest Decembers in Serbia for the 1951-2017 period relative to the 1981-2010 base period

Figure 11. 15 years ranked by the highest December totals for Leskovac for the 1925-2017 period

Figure 12. 15 years ranked by the highest December totals for Kursumlija for the 1925-2017 period

Figure 13. 15 years ranked by the highest December totals for Nis for the 1925/2017 period

Daily precipitation maximum of 53.6 mm was measured in Kursumlija, on December 1, thereby breaking the previous December record of 53.5 mm set on December 3, 1935. On December 2, Dimitrovgrad received 43.9mm of precipitation, thereby besting the previous December precipitation record of 38.4 mm, set on December 17, 1962.

The number of days with precipitation in December ranged from 9 days in Kragujevac to 20 days at Kopaonik. In most of Serbia, there were 1 to 4 days with precipitation above the December average.

Figure 19 shows assessment of the air temperature and precipitation sums in Serbia for December based on the tercile distribution relative to the 1981-2010 base period. It can be noted that December 2017 was marked by precipitation sums above the upper tercile and above-average temperatures.

Figure 14. Assessment of air temperature and precipitation for December in Serbia with the accompanying terciles compared to the 1981-2010 base period

Snow cover was registered across most of Serbia, aside from Negotin. The number of days with snow cover ranged from 1 in Zajecar to 12 days in Dimitrovgrad, and on the hilly-mountainous regions from 20 days on Crni Vrh to 31 days at Kopaonik. The number of days with snow cover was 3 to 11 days below the December average in most of the country.

Figures 15, 16, 17 and 18 show daily and cumulative precipitations sums in Belgrade, Dimitrovgrad, Kursumlija and Kopaonik.

Figure 15.

Figure 16.

Figure 17.

Figure 18.

SUNSHINE DURATION (INSOLATION)

Sunshine duration in December ranged from 43.1 hours in Vranje to 93.1 hours in Sombor (Figure 19).

December insolation ranged from 65% at Kopaonik to 176% in Sombor relative to the normal for the 1981-2010 base period (Figure 20).

Note: Climate analysis of the meteorological elements was performed on the basis of the data obtained from 28 main meteorological stations.

Figure 19. Insolation, expressed in hours during december 2017

Figure 20. Insolation expressed in the percentages of normal during December 2017