MONTHLY BULLETIN FOR SERBIA

July 2017

Belgrade, 4th August 2017

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

July 2017 ranks as the fourth warmest for Serbia, and the third warmest for Smederevska Palanka and Banatski Karlovac. Zrenjanin observed third driest July while Novi Sad and Crni Vrh experienced fifth driest July. Two heat waves were observed. Record-breaking number of tropical nights was recorded in Zrenjanin.

Overview of the synoptic situation *

Alteration of the period with very warm and somewhat cooler/unsettled weather

The beginning of the month was characterized by further disruption of the ridge above our territory. Namely, in southwestern upper air circulation, within the ground cyclone located above the central part of the continent, frontal zone was slowly transferring southeastward from northwest with the gradual drop of geopotential across the Balkans. After the passage of the front overnight to 2 July, and subsequently, the axis of the upper air trough spreading in the northeast-southwest direction, rise of the air pressure in the ground and short-term establishment of north-northwesterly upper air circulation took place across our country. Weather was changeable, rain firstly affected northern and northwestern areas, with thunders at places, spreading to the remainder of the country, with intermittent rain in central and southern areas where thunderstorms were recorded.

As of July 4, the period was characterized by the gradual rise of geopotential above the Balkans and Mediterranean due to the intensive advection of the warm air mass from northern Africa in the lower troposphere layer as well as of the cyclone development above the Atlantic Ocean at the Pyrenean Peninsula with the maintenance of northwesterly upper air circulation weakly expressing above the Balkans. At the beginning of the second decade, weather was influenced by establishment of the ridge and very warm air mass. The maximum air temperature surpassed 35 degrees across the entire country. The beginning of the second decade, the weather was influenced by establishing of ridge and very warm air mass. The maximum air temperature exceeded 35 degrees across the entire country.

Overnight between 12 and 13 July, the disruption of the ridge took place due to the impact of the cold atmospheric front from northwest. Weather in Serbia and its wide vicinity the following days, until 18 July, was influenced by cyclone development in northwestern Europe and its transfer toward east-southeast, and west-northwest upper air circulation above the Balkans and southern Europe with the series of cold fronts in the above mentioned circulation above the Pannonian Plain and parts of northern areas of the Balkans. The weather was changeable with scattered precipitation, somewhat more pronounced on July 12 in western Serbia, and the following day in central and southern parts of the country. In the remaining days, the weather was dry.

The second heat wave during the month occurred between 18 and 24 July. The maximum air temperature exceeded 35 degrees. The similar synoptic situation was marked by the increase of wave amplitude across the eastern Atlantic and the British Isles as well as the development of cyclone across all altitudes along with the advection of warm air mass from northern Africa across the central Mediterranean and Italy to the Balkans.

This developed and spatial cyclone above the Western Europe and frontal system within it, on the evening of July 24 occupied the space of central Europe, Pannonia Plain and western

Mediterranean, by further moving toward west-northwest affected the shift in weather conditions here, first in northern and western areas, and consequently the rest of the country. Hence, the following days until July 27 were marked by scattered showers and thunderstorms, cooler weather compared to the previous period with the increased northwesterly wind. The mentioned cyclone and the accompanying upper air trough were slowly transferring eastward, but as of July 28 the gradual rise in the ground air pressure took place along with the establishment of the northwesterly circulation, and subsequently of the rise of geopotential.

Subsequently, until the end of the month, establishing of the ridge above parts of central and southern sections of the continent with the ridge axis across Serbia was caused by the advection of warm air mass from northern Africa toward western and central Mediterranean within the developed system of low air pressure above the Atlantic and British Isles. It was followed by a warm period, during which tropical days were recorded. In western and northern areas, the weather conditions were unstable characterized by showers and thunderstorm of short duration.

* Division for aviation meteorological forecast

Air temperature

Mean monthly air temperature Mean air temperature in July ranged from 14.4ºC at Kopaonik to 25.9ºC in Belgrade (Figure 1).

The departure of the mean monthly air temperature from the normal1 for the 1981–2010 base period ranged from 0.8ºC in Zajecar to 2.9ºC in Belgrade (Figure 2).

Based on the percentile method2, mean air temperature in July was in the categories of very warm and extremely warm across most of the country, normal category in Zrenjanin, and warm category on Palic, Sombor, Kikinda 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 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 3. Spatial distribution of the mean monthly

air temperature using percentile method during July 2017

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

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

Based on the percentile method, mean daily air temperature in Belgrade was in the categories of very warm and extremely warm at the end of first and the beginning of the second decade, as well as at the beginning and end of the third decade (Figure 4).

Figure 4. Monthly course of the mean daily air temperature in Belgrade during July 2017

July 2017 was the fourth warmest in the 1951-2017 period (Figure 5) and the third warmest for Banatski Karlovac and Smederevska Palanka (Figure 6).

Figure 5. Rank of the warmest and coldest July for Serbia for the 1951-2017 period

Figure 6. Rank of the 15 record warm Julies in descending order for Smederevska Palanka for the 1939-2017

period Figure 7 shows the assessment of the air temperature and precipitation in Serbia for July based on the tercile distribution relative to the 1981-2010 base period. It can be noted that July 2017 was characterized by air temperature significantly above upper tercile and precipitation sums near lower tercile.

Figure 7. Assessment of air temperature and precipitation in July for Serbia with the accompanying terciles

relative to the 1981-2010 base period

Maximum air temperature The mean maximum air temperature in July ranged from 19.0ºC at Kopaonik to 32.8ºC in Smederevska Palanka.

Based on the percentile method, mean maximum monthly air temperature in July in Serbia was in the categories of very warm and extremely warm, whereas in Palic, Sombor, Kikinda, Crni Vrh, Zajecar and Vranje it was in the warm category.

The highest maximum daily air temperature of 40.0ºC was measured in Smederevska Palanka on July 11.

Serbia observed two heat waves3 in July. The first one affected most of the country, lasting from 6 to 12 July at most places. The onset of the second heat wave was observed in Belgrade on 19 July, and in Kikinda, Zrenjanin, Veliko Gradiste, Smederevska Palanka and Banatski Karlovac on July 20, with the duration until 24 July (Chart 1).

Chart 1. Heat waves in Serbia during July 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

Summer days4 were recorded across the entire country. In the upper land, their number varied from 1 day at Kopaonik to 17 days at Zlatibor and Sjenica. As for the low-lying areas, their number was in a range from 24 days in Pozega to 31 day in Smederevska Palanka and Veliko Gradiste, which is up to 6 days (at Crni Vrh up to 8 days) above the July average.

Tropical days5 were recorded across most of Serbia aside from Kopaonik. Their number was the following: 2 days at Crni Vrh, 5 days at Zlatibor, and 6 tropical days in Sjenica. In the lowland, the number of tropical days ranged from 15 days in Kikinda to 23 in Negotin, which is 3 to 9 days above the July average in most of the country.

Figure 8 shows monthly course of the maximum daily air temperature for Belgrade in July 2017 along with monthly course for July 2012 and 2015, which were warmer. July 1928 was also warmer than July 2017.

Figure 8. Monhtly course of the maximum daily air temperature in Belgrade in July 2012, 2105 and 2017

Minimum air temperature Mean minimum July air temperature ranged from 9.5ºC in Sjenica to 19.0ºC in Belgrade.

Based on the percentile method, mean minimum monthly air temperature was in the categories of normal and warm in most of the country, very warm in Valjevo, Zlatibor, Kursumlija, Cuprija and Nis, and extremely warm in Belgrade.

4 Summer day refers to a day with maximum air temperature 25°C and above 5 Tropical day refers to a day with maximum air temperature 30°C and above

The lowest minimum daily air temperature of 4.1ºC was measured in Sjenica on July 5. In the lowland, the lowest minimum daily air temperature of 8.3ºC was observed in Dimitrovgrad on July 5.

The number of registered tropical nights6 ranged from 2 to 7 in most of Serbia. Zrenjanin observed 9 nights and Belgrade experienced 13 tropical nights. The maximum number of tropical nights for Jul was exceeded in Zrenjanin, thereby breaking the previous record of 8 nights, set in July 2011 and 2015.

PRECIPITATION

The registered amount of July precipitation ranged from 8.9 mm in Zrenjanin to 99.3 mm at Kopaonik (Figure 9).

Precipitation totals compared to the normal for the 1981-2010 base period ranged from 15% in Zrenjanin to 113% in Sremska Mitrovica (Figure 10).

Based on the percentile method, precipitation sums were in the categories of dry and normal across most of the country, extremely dry in Novi Sad and Zrenjanin (Figure 11).

6 Tropical night refers to a day with minimum daily air temperature 20°C and above

Figure 11. Monthly precipitation sums according to the percentile method

Figure 9. Spatial distribution of the monthly precipitation sums (mm)

Figure 10. Spatial distribution of the monthly precipitation sums in the percentages of normal for the 1981–2010 base period

July 2017 was the third driest for Zrenjanin (Figure 12), and fifth driest for Novi Sad and Crni Vrh.

Figure 12. Rank of the top 15 wettest Julies for Zrenjanin for the 1925-2017 period

In July, the highest daily precipitation total of 46.3 mm was measured in Kursumlija on July 26.

The number of days with precipitation in July ranged from 5 days in Kragujevac, Negotin and Vranje to 11 days in Zrenjanin and Loznica, which is 5 days below the July average.

Daily and cumulative precipitation sums with averaged normals 1981-2010 for July for Belgrade, Sremska Mitrovica and Kopaonik are shown in Figures 13, 14 and 15.

Figure 13.

Figure 14.

Figure 15.

SUNSHINE DURATION (INSOLATION)

Sunshine duration in July ranged from 280.6 hours in Nis to 363.8 hours in Novi Sad (Figure 16).

July insolation ranged from 98% in Nis to 135% in Pozega relative to the normal for the 1981-2010 base period (Figure 17).

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

Figure 16. Insolation, expressed in hours during July 2017

Figure 17. Insolation expressed in the percentages of normal during July 2017