Yes

you do need a jacket based on the weather in Chelmsford, UK 1 second ago

Why? Because there are strong winds blowing out there!
65°F18°C & Windy

Wind is 16 mph25 km/h from the West, gusting to 30 mph48 km/h
September 16
10am65°F18°C16 mph26 km/h WestWindy
11am65°F18°C15 mph24 km/h WestWindy
12pm65°F18°C14 mph22 km/h WestMostly Cloudy
1pm63°F17°C12 mph20 km/h WestCloudy
2pm61°F16°C10 mph16 km/h WestMostly Cloudy
3pm59°F15°C9 mph14 km/h WestCloudy
4pm58°F14°C9 mph14 km/h WestMostly Cloudy
5pm57°F14°C8 mph13 km/h WestMostly Cloudy
6pm55°F13°C8 mph13 km/h SouthwestMostly Cloudy
7pm54°F12°C8 mph13 km/h SouthwestMostly Cloudy
8pm54°F12°C7 mph12 km/h SouthwestCloudy
9pm54°F12°C7 mph11 km/h SouthwestCloudy
DateLowHighWindDayNight
September 1553°F12°C65°F18°C14 mph22 km/h from WestMostly CloudyDrizzle
September 1653°F12°C67°F20°C14 mph23 km/h from SouthwestRainCloudy
September 1762°F17°C73°F23°C15 mph24 km/h from SouthwestWindyMostly Cloudy
September 1859°F15°C77°F25°C9 mph14 km/h from SouthPartly CloudyPartly Cloudy
September 1957°F14°C71°F21°C7 mph12 km/h from SouthDrizzleRain
September 2051°F11°C61°F16°C14 mph23 km/h from NorthwestRainRain
September 2150°F10°C61°F16°C17 mph27 km/h from NortheastWindyMostly Cloudy

Yes

Low of 54°F12°C, High of 67°F20°C
Wind: 14 mph23 km/h
Precipitation: 85% rain

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