The UK weather is set for a “Super Saturday” of sunshine hotter than Australia with 19C of heat.
That makes the south 9C hotter than average and hotter than 14C Melbourne.
But a dramatic weather map shows cold air arcing to Britain from Greenland as Sunday begins.
Snow flurries will be threatening in the north on Sunday and Tuesday, with gales following.
It comes as part of a 700-mile wide “polar plume”.
There will be highs of just 7 to 11C for most of Sunday, and Met Office maps also show the jet stream steering cold air south from Greenland to Britain.
“Sunday will feel colder, with a frosty Monday with wet and windy weather in the north”
Weather Outlook forecaster, Brian Gaze, said: “After a ‘Super Saturday’ with lots of sunshine for the South, it’s a ‘Shivering Sunday’ to start British summertime as cold air filters in from their Greenland.”
And a Met Office forecaster added: “Sunday will feel colder, with a frosty Monday with wet and windy weather in the north.
“Tuesday’s showers have some sleet and snow over hills in the north.
“The period is most likely to remain unsettled, with showers heaviest in the north and wintry over hills, with overnight frosts likely.
“It will also become generally windy, with gales possible, especially towards the north-west.”
However, the hottest spring since records began is on the cards as the Met Office backed a much-hotter-than-normal three months until June.
Above average temperatures from March to May is five times more likely than much cooler conditions, the Met Office said.
The Met Office three-month forecast said: “For March-May, the probability UK average temperatures will fall into the warmest of our five categories is 50%.
“The coldest category is 10%.”
And Gaze added: “With computer models strongly favouring a warm spring, there is potential for the record for the hottest spring to be challenged.”