Millions of Britons could see tornadoes tomorrow as the first day of a "lively weekend" of thunderstorms begins.
On Friday, a notice from Paul Knightley, the head of the Tornado and Storm Research Organisation (Torro) said that low cloud bases and a "convergence zone" could come together to form a funnel.
Knightley said such conditions could arise following storms in central, south and southeast England, the East Midlands and East Anglia on Saturday afternoon.
"There's a small risk of a brief tornado from these," he said.
At the same time, the Met Office has upgraded its thunderstorm weather warnings for the weekend - one of which has been bumped up to an amber alert.
MET OFFICE
|PICTURED: The Met Office's triple weather warnings for Saturday
Two existing yellow warnings were in force on Friday - the first, on England's east coast from Lincolnshire to Berwick-upon-Tweed, and the second across London, Kent and the South East.
On Saturday, a 21-hour-long yellow storm warning starting from midnight has been slapped on all parts of England except the South West.
"Heavy rain, with some thunderstorms, may lead to disruption in places on Friday night and through much of Saturday," the Met Office warns.
Forecasters have also handed an amber warning to parts of southeast England from Portsmouth to Cambridge.
The alert, in place from 4am to 11am, warns of "torrential" rain, thunderstorms and "significant surface water flooding".
GETTY
|Low cloud bases and a 'convergence zone' could come together to form a funnel, Torro chief Paul Knightley said
Further north, southeast Scotland has been issued a yellow rain warning from 4pm tomorrow to midday on Sunday.
Then, Devon and Cornwall has been told to brace for the same - this time, from midday on Sunday to 3am on Monday.
The Met Office's chief meteorologist, Andy Page, said: "Intense rainfall will impact parts of the UK as thunderstorms move in from France.
"A range of severe weather warnings have been issued, including an amber warning covering southeast England and London.
PA
|London is in the middle of the Met Office's amber storm warning for Saturday
"The intense rainfall could lead to surface water flooding as well as frequent lightning and hail too.
"The situation is evolving, and warnings may be changed or added.
"This weekend is expected to be busy on the roads as more schools in England and Wales break up for the summer holidays, so it's important people keep up-to-date with the very latest forecast.
"There will be spells of more pleasant weather in parts of the UK through the weekend, with some sunny spells in between systems as they move through."