Due to a technical error, test warnings mistakenly appeared on our website and apps. The issue has now been resolved.— Met Office (@metoffice) May 5, 2016
The amber snow alert made was for London, south-east England, and south Wales - despite temperatures reaching 21C (70F).
The Met Office blamed a "technical error", reports the BBC.
"The snow alert for Thursday evening was a test warning that accidentally went live on the Met Office website and mobile phone application," it said.
The warning was also emailed to subscribers, with many taking to social media in confusion.
"As if my dad just got an email from the Met office with an amber warning for snow in the south west. Mate, have you looked out the window?" wrote Twitter userBriony.
Essex Weather Centre tweeted: "Looks like the sun has got to someone at the Met Office! Definitely no snow expected this evening or overnight!"
The Met Office later confirmed that Thursday had been the warmest of the year so far, with temperatures expected to continue to rise over the weekend.
Sunday is expected to be the hottest day, with the temperatures expected to reach 26C (79F) in London and 21C (70F) in Edinburgh - hotter than parts of Spain and Los Angeles.
The average UK temperature for May is 14C (57).