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, No, you don't need a jacket.

Based on the weather in Watford, UK as of May 25, 2020 2:43pm local time.

Now

Clear
Temp: 74°F24°C
Wind: 6 MPH10 KPH
Precipitation: None

Today

Next 2 hours: No

Next 4 hours: No

Next 8 hours: No

Tomorrow

Yes

Mostly cloudy throughout the day.
Low of 51°F11°C, High of 76°F25°C
Wind: 4 MPH6 KPH
Precipitation: 7% rain