The arrival of British Summer Time has brought wet and windy weather, with snow already falling in some parts of the country.
Stephen Davenport, forecaster with MeteoGroup, the weather division of the Press Association, said snow had fallen in the far north of Scotland and there will be more to come.
Temperatures dropped to freezing in Glencoe and minus 2C (28.4F) in Glenshee as the snow fell.
Mr Davenport said: "It's not a surprise for that part of the country in March.
"We could eventually see 5cm-10cm (2in-4in) of snow over the hills and maybe a slight slushy covering in Glasgow.
"The hills in northern England and maybe North Wales will see a slight covering on Wednesday.
"Everywhere will see temperatures dropping below average. It will get wet and windy but the snow will be confined to those northern areas."
Earlier predictions said the cold snap is likely to only last two days, with better weather coming by the end of the week.
Julian Mayes, senior forecaster with MeteoGroup, said: "It should be milder by Friday, with rain coming in from the south west, but unfortunately it does look an unsettled picture over the Easter weekend."
The country has seen mild temperatures for the best part of 10 days.
Mr Mayes said: "The month started cold, but the warmer temperatures recently have taken the whole month up to about average for March. The highest reading of the year so far was one of 18C (64F) in Norfolk on March 18.
"But it's not unusual to get a northerly blast in springtime."