Restrictions on flights in and out of the UK will remain in place until at least 1am on Sunday, air traffic control company Nats said.
The ash cloud created by an erupting volcano in Iceland is "moving around and changing shape", Nats said.
If it "moves sufficiently", some domestic flights may be able to take off from Scotland and Northern Ireland.
The cloud has prevented many flights from entering or leaving the UK since noon on Thursday - at a huge cost to the industry.
Airport operator BAA said passengers should not travel to its airports as no flights would take off or land today.
A Nats statement read: "The volcanic ash cloud from Iceland is moving around and changing shape.
"Based on the latest information from the Met Office, Nats advises that the restrictions currently in place across UK controlled airspace will remain in place until at least 0100 (UK time) tomorrow, Sunday April 18.
"We are looking for opportunities when the ash cloud moves sufficiently for us to make some airspace available within Scotland and Northern Ireland, which may enable some domestic flights to operate under individual co-ordination with ATC (air traffic control); we will be co-ordinating this closely with airlines and airports.
"It is most unlikely that many flights will operate today and anyone hoping to travel should contact their airline before travelling to the airport.
"We will continue to monitor Met Office information and review our arrangements in line with that."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article