The Met Office warned of a “marked drop” in temperatures by Wednesday, with the possibility of sleet in the Central Belt and snow in the Highlands.
Meteorologist Alex Deakin said: "It may well be the shortest weekend of the year, because the clocks go forward, but it will be one of the sunniest.
"It's going to be blue skies almost across the board on both Saturday and Sunday thanks to a chunky area of high pressure that's just wobbling around across the UK.
Mr Deakin said temperatures were expected to widely reach "15 to 18C, maybe 19 or 20 in one or two locations in the south."
However, a cold air mass pushing in on Tuesday is forecast to bring unsettled and wet conditions and lower temperatures from the middle of the week.
The Met Office said: "Next week will certainly be more on the cloudy side, and this time of year when we don't have the sunshine, it's not going to feel as warm.
"Certainly very different to this week, but it's spring.
"Spring's a fickle season – it gives you one thing one week and then the next week it will give you something very different – that's what keeps us on our toes."
The agency said wintry showers were possible across the UK, especially in the north and east, though any snow will likely be limited to high ground in the north.
Chief meteorologist Paul Gundersen said: "Although the UK has had a good deal of fine and settled March weather in recent days, a change is on the way from the middle of next week with colder air spreading down from the north and the increasing likelihood of rain for most areas.
"With the influence of some unsettled weather, we'll be seeing a marked drop in temperatures for most with colder air arriving from the north.
"This will see maximum temperatures drop into single figures for many areas, and below freezing overnight."