Ash could reach northern Scotland by midday on Tuesday and other parts of Britain, western France and northern Spain by Thursday or Friday if nothing changes, weather officials said.
A spokeswoman for Eurocontrol, which coordinates air traffic flows, declined to comment, referring to the latest published updates which ruled out major problems in the next 24 hours.
The new warning assumes the volcano will continue to spew ash at the same rate and there is no change in forecasts over a period of five days, both of which are uncertain.
Saturday's disruption took place amid mobile, low-pressure air in the north Atlantic whose movement is not easy to predict.
That contrasts with a stable high-pressure weather pattern during a crisis a year ago when a pervasive and slow-moving cloud of ash forced a six-day shutdown of European airspace, stranded tens of thousands of people and damaging economies.
On Sunday, Britain was considering whether to send up a special aircraft capable of monitoring the concentration of ash, but a decision had been taken, officials said.

A cloud of smoke and ash is seen over the Grimsvoetn volcano on Iceland on May 21, 2011. The cloud rising up from Grimsvoetn as a result of the eruption was seen first time around 1900 GMT and in less than an hour it had reached an altitude of 11 kilometres (6.8 miles)," according to the Icellandic meterological institute. |