Dense fog will blanket the UK just hours after Brits basked in the sun with the Met Office issuing a yellow weather warning ahead of the ‘challenging conditions’.
A new map indicates swathes of the northeast will be covered as visibility is predicted to drop as low as 50 metres.
There are warnings of slower journey times and delays to bus and train services in addition to cancelled flights.
A Met Office spokesman said: ‘Fog will continue to develop across parts of northeast England, Yorkshire and Humberside through Sunday night.
‘Some dense fog is likely in places with the visibility falling to 50 metres at times. Fog will lift during Monday morning.’
Motorists are advised to leave extra time to travel or amend plans where necessary and ensure fog lights are switched on if needed.
The weather warning is in place until 9am today.
It comes after families flocked to beaches and parks this weekend as Britain basked in warm sunshine during the hottest weekend of the year so far.
There are warnings of slower journey times and delays to bus and train services as well as cancelled flights (file image)
Weather forecasters predicted a warm and sunny Sunday, with sunshine seen here in Richmond
A new map indicates swathes of northeast England will be covered and visibility is predicted to drop as low as 50 metres
Yesterday afternoon was due to reach an unseasonal 20C (68F), after 19.1C (66.4F) was recorded on Saturday – warmer than Ibiza or the Amalfi Coast.
Children built sandcastles on beaches from Weston Super Mare, Somerset, to Lytham St Annes in Lancashire.
Meanwhile, outdoor swimming pools were busy and owners of beach huts in Bournemouth took advantage of the spring conditions to give the chalets a spruce-up.
As well as the throngs out picnicking and sunbathing, early risers made their way to the summit of Glastonbury Tor to enjoy a vivid sunrise.
But the sunny skies were perhaps less welcome at the Lecht ski centre in the Cairngorms, where only patches of snow remained on ski slopes which normally still have a few more weeks of wintry life in them.
Average UK daily maximum temperatures for early to mid-March are 8-11C (46-52F).
Saturday’s high was recorded at Bridgefoot, Cumbria, beating the previous warmest day of the year on Thursday when Santon Downham, Suffolk, reached 19C.
Yesterday, top temperatures of 18-19C (64-66F) were expected in London and the Home Counties, the south-west Midlands, east Wales, Cumbria and north Lancashire.
A swimmer still wants to keep their hair dry and put on a woolen hat while swimming in Clevedon on Saturday
Forecasters predicted isolated spots within those regions could reach 20C.
It compared with highs of 15-16C on the Balearic island of Ibiza, 18C on Italy’s Amalfi Coast, and 19C in Marrakech, Morocco.
But warning from the Meteorological Office of an abrupt ‘change in the very warm and dry conditions of late’ loomed over the sunny skies.
While the mild air is due to continue initially in the south east today, elsewhere a band of rain is due to move south, bringing much cooler conditions.
Overnight frosts are also set to return, initially on high ground in northern England, with lows of -2C (28F) but spreading even to central and southern England by midweek.
And wintry weather is possible in the Pennines as far south as Derbyshire by Wednesday and Thursday, with sleet and snow showers forecast on high ground.
Daytime temperatures of just 8C (46F) are expected even in the far south by Thursday and highs of just 6C (43F) further north.
Met Office deputy chief meteorologist Chris Bulmer said: ‘A frontal zone will move south across the UK during Sunday night and Monday with much colder air following from the north.
‘With these cold northeasterly winds, we are likely to see some wintry showers across the north and the east of the UK next week, but any accumulations of snow are likely to be largely restricted to hills. We’ll also see a return to overnight frosts in many areas.
People enjoy the warm weather in Weston-super-Mare in Somerset on Sunday
‘While there is uncertainty in the extent of rain and wintry showers through the middle of next week, there is higher confidence that below average temperatures will continue through the week, bringing a very different feel to the mild weather over the weekend.’
Forecasters are uncertain of the weather for the rest of March.
The Met Office said the end of the coming week and into next weekend, the ‘cool, easterly theme’, is due to continue with showers in the east but mostly dry weather elsewhere. However, there is a chance of some rain on the south coast.
It added: ‘The following week is likely to see a transition to more unsettled conditions with spells of stronger winds and some rain in many areas, but perhaps more especially the north and west. The south and east could see the best of the drier interludes between times.’
Unsettled weather is due to continue for the remainder of the month although temperatures are likely to rise again.
