Rain density

The Guardian  -  Half a month’s rainfall could hit the UK in the next 24 hours, the Met Office said on Sunday, issuing weather warnings across the country. Yellow weather warnings for rain and thunderstorms were in place in Northern Ireland, Scotland and the north and south-west of England until 10pm on Sunday, with more warnings coming into force in other areas on Monday.

Eastern parts of Northern Ireland were to be covered by a 24-hour weather warning, from 6pm on Sunday until 6pm on Monday, with heavy rain expected to cause some disruption and possibly flooding. ...

Northern Ireland records an average of 89mm of rain in July, meaning more than half a month’s rainfall could hit it in less than a day.

Flooding is also possible, the Met Office said, and parts of England and Scotland may also have 20-40mm of rain in just two hours on Monday...

More than 10 flood alerts remain active in Scotland, and where there is flooding or lightning the Met Office has warned trains and bus services may be delayed or cancelled.

Sam Smith  - Shortly before coming across this article I was outside in Maine when rain started and in a few minutes was pouring at a density I couldn't recall. Rain density is something to keep an eye out for.