Yes

you do need a jacket based on the weather in Osaka, Japan 1 second ago

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

Wind is 5 mph8 km/h from the E, gusting to 9 mph15 km/h
March 28
10am56°F13°C5 mph9 km/h ERain
11am56°F13°C4 mph7 km/h SERain
12pm57°F14°C5 mph8 km/h SERain
1pm58°F15°C6 mph10 km/h SEDrizzle
2pm59°F15°C8 mph13 km/h SERain
3pm59°F15°C9 mph14 km/h SRain
4pm61°F16°C10 mph16 km/h SWRain
5pm61°F16°C19 mph31 km/h SWRain
6pm59°F15°C15 mph24 km/h SWDrizzle
7pm57°F14°C12 mph19 km/h SWDrizzle
8pm59°F15°C10 mph17 km/h SWMostly Cloudy
9pm61°F16°C12 mph19 km/h SWPartly Cloudy
DateLowHighWindDayNight
March 2741°F5°C67°F19°C5 mph9 km/h from SERainRain
March 2856°F13°C68°F20°C12 mph19 km/h from SWDrizzleClear
March 2954°F12°C67°F19°C9 mph15 km/h from SWPartly CloudyPartly Cloudy
March 3052°F11°C70°F21°C5 mph9 km/h from SWMostly CloudyPartly Cloudy
March 3153°F12°C71°F22°C8 mph13 km/h from SWMostly ClearPartly Cloudy
April 148°F9°C67°F20°C6 mph9 km/h from NPartly CloudyMostly Cloudy
April 250°F10°C70°F21°C5 mph7 km/h from NWMostly CloudyMostly Cloudy

Yes

Low of 55°F13°C, High of 68°F20°C
Wind: 12 mph19 km/h
Precipitation: 67% rain

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