Heavy fog warnings have been issued for parts of the UK with a chance of cancelled flights and travel chaos.
Large swathes of the south west,including much of Devon and Cornwall, and the north west, around Liverpool and Manchester, are affected.
The Met Office has warned that dense fog patches could cause slower journey times on the roads and rails.
Air passengers have been told to expect possible delays to journeys or cancellations in the most extreme examples.
Busy airports in the impacted areas include Bristol, Manchester and Liverpool.
UK weather forecast: Temperatures to drop by 18C as Arctic vortex hits this weekend
However, at this stage it is unclear whether flights have been affected at any of the locations.
The severe weather warning is in place until 10am this morning by which time the worst of fog will have cleared.
The dense fog comes ahead of a weekend freeze UK weather forecast: Temperatures to drop by 18C as Arctic vortex hits this weekend
The sudden drop, of up to 18C in places, will come in stark contrast to the mini-heatwave that Britain has been enjoying this week.
UK weather forecast: Britain hotter than BARCELONA - but snow and cold to hit
A Met Office forecaster said: "There will be rain and strong winds at times, mainly in the northwest of the UK, where gales are likely.
"Some rain is possible in the south too, but there will be more in the way of dry weather.
"The unsettled weather is likely to continue into mid April."
Although this weekend heralds the official start of British Summer Time, the first week is set to be blighted by widespread frosts.
Thundery rain is expected to lash the country by Tuesday, with the north and northeast again worst affected.
Gales are also expected to reach speeds of 40mph in Scotland and Northern Ireland - with slower but still blustery gusts in England.
The highest temperatures will again hover in the top-end of single figures - but could remain around 11C in the southwest.
