The fog that settled across London has slowly begun to lift, with flights returning to normal as visibility improves.
Lara Gunn, spokesperson for weather forecasters MeteoGroup, said: "A dense fog is hanging over the southeast and up towards the Midlands and is expected to linger.
"Visibility will be quite poor in some areas and travellers should take caution."
The Met Office said the fog would begin "slowly clearing" across London and the southeast.
Around 100 flights were cancelled as a result of the fog at London's Heathrow and City airports. All flights at City Airport, which was enveloped in fog, were cancelled until midday.
Management said that travel disruptions were continuing but that flights were getting back to normal.
But with the fog dissipating, forecasters have warned that the UK is in for severe storms.
The Met Office has put out a severe weather warning for Scotland and Northern Ireland over the weekend, with severe gales expected.
"South to southwest winds will increase across many northern parts of the UK on Saturday with gales becoming widespread across Scotland and Northern Ireland," said the forecast.
"There is the potential for severe gales to develop, particularly across northwest Scotland. Gusts of 60-70mph are likely with a risk of gusts to 80mph or more across exposed parts of northwest Scotland.
"Some heavy rain is also likely, particularly in the west. The public should be aware that there could be disruption to travel and other outdoor events. At this stage there remains uncertainty regarding the extent of the strongest winds and so the public are advised to look out for updates to this alert in the coming days."
Jonathan Powell, of Vantage Weather, also warned that severe weather could continue through to January.
"We have a succession of low-pressure systems barrelling in from the Atlantic which are going to trigger these storms," he told the Express.
"The jet stream is shifting southwards which is the main problem, but it is going to make things very stormy right through Christmas and into the New Year.
"Gales will become more widespread from next week with 90mph gusts likely in exposed regions. There is also going to be up to two inches of rain."