No

Why? Because you should be inside at home! #StayHome

But if you absolutely had to go out to get groceries, medication or other essential travel, Yes, you do need a jacket.

Why? Because it's not very warm out.

Based on the weather in Cardiff, UK as of May 27, 2020 3:12am local time.

Now

Partly Cloudy
Temp: 57°F14°C
Wind: 7 MPH12 KPH
Precipitation: None

Today

Next 2 hours: Yes

Next 4 hours: Yes

Next 8 hours: Yes

Tomorrow

Yes

Partly cloudy throughout the day.
Low of 56°F14°C, High of 74°F24°C
Wind: 8 MPH13 KPH
Precipitation: 3% rain