Snow was cleared from the runway at Durham Tees Valley Airport
More flights have been cancelled from Durham Tees Valley Airport as the freezing conditions continue to affect County Durham and Wearside.
Eastern Airways flights, to and from Southampton and Aberdeen on Friday, have been cancelled.
Almost 40 schools across County Durham and Wearside will also be closed on Friday.
And drivers in Durham are warned some minor roads will not be gritted because of "uncertainty" over salt supplies.
Durham County Council said it would continue treating A and B roads for as long as possible but was coping with "very difficult" weather conditions.
A county council spokesman said so far gritters had spread more than 30,000 tonnes of salt and grit and more than £3m had been spent maintaining the highway network and priority footpaths.
He said: "The council will continue to plough all priority 1 and 2 routes, but only A and B category roads will be treated with salt.
"We will continue to keep the situation under review and as soon as more salt becomes available we will reprioritise.
"It is important that everyone understands we are managing very difficult ongoing winter conditions with restricted supplies."
On Thursday a stretch of the A1(M) was closed, southbound between Carrville and Bowburn, for about three hours when a lorry jackknifed.
The closure, along with the weather conditions, resulted in severe congestion in and around Durham City during the morning rush hour.