Parts of Scotland including the Highlands will also experience snowfall, albeit much heavier than below the border.
On the same date, much of the North and the Midlands will be lashed with heavy rains.
The rain will affect Middlesbrough, Morecambe and Blackpool.
But following the early May washout and cold snap Britons are set to bask in balmy temperatures.
A weather chart from WX Charts shows temperatures topping 18C in King’s Lynn on May 18.
London is expected to experience temperatures of 17C while Manchester will be 15C.
Strong winds will also be felt in southern Wales.
While the sunny snap will be welcomed by Britons, many are keen to head abroad as soon as travel restrictions are rolled back.
On Monday Boris Johnson said the approach to foreign travel this summer will be sensible and cautious to avoid “an influx of disease”.
While Britons have being enjoying increased freedoms since last month, Europe is battling a third wave of Covid.
The Prime Minister said there will be “some opening up” on May 17, but that things must be done in a way “to make sure that we don’t see the virus coming back in” to the UK.
His cautious tone came as some MPs called for restrictions on foreign holidays to be maintained to protect the country from new Covid-19 variants.
Labour leader Sir Keir Starmer stopped short of calling for the ban to be continued but urged a “careful” approach.
During a campaign visit to Hartlepool, Mr Johnson said: “We do want to do some opening up on May 17 but I don’t think that the people of this country want to see an influx of disease from anywhere else.
“I certainly don’t and we have got to be very, very tough, and we have got to be as cautious as we can, whilst we continue to open up.”