Yes

you do need a jacket based on the weather in San Antonio (San Antonio International Airport Vicinity), Texas, United States 1 second ago

Why? Because rain's coming down and it's on the windy side!
78°F26°C & Rain

Wind is 7 mph12 km/h from the Southeast, gusting to 22 mph35 km/h
July 4
1am78°F26°C8 mph13 km/h SoutheastThunderstorms
2am77°F25°C8 mph12 km/h SouthCloudy
3am77°F25°C8 mph13 km/h SoutheastCloudy
4am76°F25°C8 mph13 km/h SouthThunderstorms
5am76°F24°C8 mph13 km/h SouthThunderstorms
6am76°F24°C8 mph13 km/h SouthThunderstorms
7am75°F24°C8 mph12 km/h SouthCloudy
8am75°F24°C7 mph12 km/h SouthCloudy
9am76°F24°C8 mph13 km/h SouthCloudy
10am77°F25°C9 mph14 km/h SouthCloudy
11am78°F26°C10 mph15 km/h SouthDrizzle
12pm80°F26°C10 mph16 km/h SouthCloudy
DateLowHighWindDayNight
July 376°F24°C90°F32°C7 mph10 km/h from SoutheastThunderstormsThunderstorms
July 475°F24°C86°F30°C8 mph13 km/h from SouthThunderstormsCloudy
July 574°F23°C83°F28°C7 mph11 km/h from SouthRainMostly Cloudy
July 673°F23°C88°F31°C6 mph10 km/h from SouthPartly CloudyPartly Cloudy
July 773°F23°C90°F32°C6 mph9 km/h from SouthMostly ClearMostly Clear
July 872°F22°C90°F32°C6 mph9 km/h from SouthMostly ClearMostly Clear
July 973°F23°C91°F33°C5 mph8 km/h from SouthMostly ClearMostly Clear

No

Low of 75°F24°C, High of 86°F30°C
Wind: 8 mph13 km/h
Precipitation: 52% rain

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