Parts of Denmark, southern Norway and southwest Sweden could be impacted by high density ash on 25 May, according to Eurocontrol.
A total of about 500 flights have so far been cancelled as a result of the ash cloud from the eruption of Iceland's Grimsvotn volcano on 21 May, said Eurocontrol. It has so far affected Scotland and northern England.
Using forecasts from the Volcanic Ash Advisory Centre in London, Eurocontrol said "there is a strong possibility that the ash cloud may impact parts of Denmark, southern Norway and southwest Sweden by tomorrow".
However, it added that "given the new procedures in place and the predicted movement of the ash cloud over the coming days, the actual impact on flights is expected to be relatively low".
British Midland International (BMI) expects to resume a normal flying programme on 25 May, based on current forecasts.
The carrier said it has taken the decision to cancel all flights from Glasgow and Edinburgh for the remainder of 24 May, but "the changing ash cloud situation over northeast Scotland has enabled BMI to resume all flights from Aberdeen this afternoon".
British Airways has also cancelled all flights to and from Edinburgh and Glasgow, as well as Newcastle in northeast England for the remainder of 24 May, but has resumed services to Aberdeen.
Irish budget carrier Ryanair has cancelled all flights to and from Scottish airports for the remainder of 24 May, blaming its decision on the UK Civil Aviation Authority (CAA) closing the airspace over Scotland.
However, the CAA has responded that the airspace "is not closed, and it will not be closed" and "all airports remain open". An airline could "potentially" operate a flight in an area judged to be affected by high-density ash if it had submitted a safety case to operate in this type of ash, but no UK carrier has done so.
The Irish Aviation Authority (IAA) said that Ryanair did submit a safety case to operate in the "red zone" at 21:00 local time on 23 May. The regulator added that it is reviewing the document but has not yet approved it - a process which "would normally take weeks".