Yes

you do need a jacket based on the weather in Winchester SO21, UK 1 second ago

Why? Because it's not very warm out!
53°F12°C & Clear

Wind is 4 mph7 km/h from the Northeast, gusting to 9 mph14 km/h
August 21
10pm52°F11°C4 mph7 km/h NortheastClear
11pm51°F11°C4 mph6 km/h NortheastClear
August 22
12am50°F10°C3 mph5 km/h NortheastMostly Clear
1am50°F10°C3 mph5 km/h NortheastMostly Clear
2am51°F11°C2 mph4 km/h NortheastMostly Clear
3am55°F13°C2 mph3 km/h NortheastMostly Clear
4am59°F15°C2 mph3 km/h EastMostly Clear
5am62°F17°C2 mph2 km/h SoutheastMostly Clear
6am65°F18°C2 mph4 km/h SouthwestMostly Clear
7am67°F19°C4 mph6 km/h WestPartly Cloudy
8am68°F20°C4 mph7 km/h WestMostly Cloudy
9am70°F21°C5 mph9 km/h WestPartly Cloudy
DateLowHighWindDayNight
August 2150°F10°C72°F22°C4 mph7 km/h from WestPartly CloudyPartly Cloudy
August 2254°F12°C71°F22°C4 mph7 km/h from NortheastMostly CloudyPartly Cloudy
August 2354°F12°C71°F22°C7 mph11 km/h from SoutheastPartly CloudyPartly Cloudy
August 2453°F12°C74°F23°C8 mph13 km/h from SoutheastPartly CloudyPartly Cloudy
August 2558°F14°C74°F23°C11 mph18 km/h from SouthwestPartly CloudyMostly Cloudy
August 2657°F14°C70°F21°C9 mph15 km/h from SouthwestPartly CloudyPartly Cloudy
August 2755°F13°C66°F19°C8 mph13 km/h from SouthDrizzleDrizzle

Yes

Low of 55°F13°C, High of 72°F22°C
Wind: 4 mph7 km/h
Precipitation: None

Support This Page