Yes

you do need a jacket based on the weather in Seoul, South Korea 1 second ago

Why? Because it's raining in your area!
72°F22°C & Rain

Wind is 2 mph4 km/h from the Southeast, gusting to 6 mph9 km/h
July 17
4pm72°F22°C3 mph5 km/h SoutheastThunderstorms
5pm72°F22°C3 mph4 km/h SoutheastThunderstorms
6pm73°F23°C3 mph5 km/h SoutheastThunderstorms
7pm73°F23°C3 mph5 km/h SoutheastThunderstorms
8pm74°F23°C3 mph6 km/h SouthThunderstorms
9pm75°F24°C4 mph7 km/h SouthRain
10pm76°F24°C5 mph8 km/h SoutheastRain
11pm77°F25°C6 mph9 km/h SouthDrizzle
July 18
12am78°F26°C5 mph8 km/h SouthThunderstorms
1am79°F26°C4 mph7 km/h SouthThunderstorms
2am79°F26°C4 mph7 km/h SouthThunderstorms
3am79°F26°C4 mph6 km/h SouthThunderstorms
DateLowHighWindDayNight
July 1772°F22°C79°F26°C4 mph6 km/h from SouthThunderstormsThunderstorms
July 1873°F23°C82°F28°C6 mph9 km/h from SouthRainRain
July 1974°F23°C87°F31°C6 mph10 km/h from SouthwestRainMostly Cloudy
July 2075°F24°C87°F30°C6 mph10 km/h from SouthwestDrizzleRain
July 2174°F24°C86°F30°C4 mph6 km/h from WestDrizzleThunderstorms
July 2274°F23°C89°F32°C3 mph5 km/h from WestDrizzleMostly Clear
July 2374°F24°C90°F32°C4 mph6 km/h from SoutheastMostly ClearMostly Clear

No

Low of 73°F23°C, High of 82°F28°C
Wind: 6 mph9 km/h
Precipitation: 74% rain

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