Yes

you do need a jacket based on the weather in Belgrade, Serbia 1 second ago

Why? Because it's cool. Pleasantly cool, but cool!
55°F13°C & Mostly Clear

Wind is 2 mph4 km/h from the South, gusting to 6 mph10 km/h
September 19
1am56°F13°C3 mph5 km/h SouthwestMostly Clear
2am59°F15°C3 mph5 km/h SouthwestMostly Clear
3am65°F19°C3 mph4 km/h SouthwestClear
4am70°F21°C3 mph5 km/h WestClear
5am74°F23°C3 mph5 km/h WestClear
6am77°F25°C3 mph6 km/h WestClear
7am78°F26°C3 mph6 km/h NorthwestClear
8am79°F26°C4 mph6 km/h NorthwestClear
9am80°F27°C4 mph6 km/h NorthwestClear
10am80°F27°C4 mph6 km/h NorthwestClear
11am79°F26°C4 mph6 km/h NorthClear
12pm77°F25°C3 mph4 km/h NorthwestClear
DateLowHighWindDayNight
September 1855°F13°C80°F27°C3 mph5 km/h from NorthwestClearClear
September 1958°F15°C83°F29°C3 mph6 km/h from EastClearClear
September 2063°F17°C86°F30°C11 mph18 km/h from SoutheastClearClear
September 2167°F20°C86°F30°C11 mph18 km/h from SoutheastClearClear
September 2265°F18°C86°F30°C7 mph11 km/h from SoutheastClearMostly Clear
September 2363°F17°C82°F28°C5 mph8 km/h from SouthwestMostly CloudyPartly Cloudy
September 2459°F15°C76°F24°C5 mph7 km/h from NorthPartly CloudyMostly Cloudy

Yes

Low of 58°F15°C, High of 83°F29°C
Wind: 3 mph6 km/h
Precipitation: None

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