European meteorologists say the cloud of volcanic ash is spreading southward over Europe and eastward into Russia at the speed of a car in city traffic.
No one is ready to predict how far it will go or when the dust will disperse in the atmosphere as long as the Icelandic volcano continues to erupt.
Helen Chivers of the British Met Office said the trajectory will take the cloud over northern France and Austria, and into eastern and central Russia.
Harry Geurts of the Dutch meteorological office said the cloud was moving southeast around 25 miles (40 kilometers) per hour from the North Sea, but normal cloud cover makes it difficult to track.
Mr. Geurts said where the dust goes depends on the wind speed and that varies at different altitudes.
