Lava and ash explode out of the caldera of Iceland's Eyjafjallajokull volcano April 22, 2010.
Airports in a few parts of Scotland are set to close again because of risks from a rise in volcanic ash levels.
The Civil Aviation Authority (CAA) said no flights would be permitted from Glasgow, Prestwick and Campbeltown between 0700 BST and 1900 BST.
However, airports in Edinburgh will stay open and Inverness airport is set to be closed in the morning only.
The CAA warned the situation "remains changeable" and advised passengers to ensure with airports before travelling.
No-flight restrictions are also expected to be introduced between 0700 BST and 1900 BST at Stornoway, Benbecula, Tiree, Islay and Barra in the Hebrides.
The situation in the skies has been varying almost hour by hour, meaning the picture for air travelers is unclear.
Emergency committee
Forecasts show the 60 nautical-mile buffer zone imposed around high concentrations of ash is close to a few northern airports.
However, the latest opinion issued by the CAA at 0200 BST said airports in Edinburgh and north-west England could safely stay open on Wednesday, despite the proximity of the ash.
In a statement, the CAA said: "The situation remains changeable, so passengers expecting to travel from airports in Scotland, Northern Ireland, the north of England and north Wales should contact their airlines to check whether their flight is operating."
The Scottish government has reactivated the emergency response committee which was formed in the wake of the flight chaos caused by the Eyjafjallajokull ash cloud last month, which left thousands of Scots stranded abroad.
Scottish Finance Secretary John Swinney said the situation remained unpredictable and had the potential to cause further disruption.
He added: "I appreciate that people will feel inconvenienced, some frustrated, at any further cancellations but I hope they will understand the need to follow the precautionary principle that the overriding consideration must be to ensure their safety."
Flights to and from the west coast islands of Tiree, Islay, Barra and Benbecula, and Campbeltown on the Kintyre peninsula, were affected by the ash on Monday evening and Tuesday morning.
The Civil Aviation Authority (CAA) said no flights would be permitted from Glasgow, Prestwick and Campbeltown between 0700 BST and 1900 BST.
However, airports in Edinburgh will stay open and Inverness airport is set to be closed in the morning only.
The CAA warned the situation "remains changeable" and advised passengers to ensure with airports before travelling.
No-flight restrictions are also expected to be introduced between 0700 BST and 1900 BST at Stornoway, Benbecula, Tiree, Islay and Barra in the Hebrides.
The situation in the skies has been varying almost hour by hour, meaning the picture for air travelers is unclear.
Emergency committee
Forecasts show the 60 nautical-mile buffer zone imposed around high concentrations of ash is close to a few northern airports.
However, the latest opinion issued by the CAA at 0200 BST said airports in Edinburgh and north-west England could safely stay open on Wednesday, despite the proximity of the ash.
In a statement, the CAA said: "The situation remains changeable, so passengers expecting to travel from airports in Scotland, Northern Ireland, the north of England and north Wales should contact their airlines to check whether their flight is operating."
The Scottish government has reactivated the emergency response committee which was formed in the wake of the flight chaos caused by the Eyjafjallajokull ash cloud last month, which left thousands of Scots stranded abroad.
Scottish Finance Secretary John Swinney said the situation remained unpredictable and had the potential to cause further disruption.
He added: "I appreciate that people will feel inconvenienced, some frustrated, at any further cancellations but I hope they will understand the need to follow the precautionary principle that the overriding consideration must be to ensure their safety."
Flights to and from the west coast islands of Tiree, Islay, Barra and Benbecula, and Campbeltown on the Kintyre peninsula, were affected by the ash on Monday evening and Tuesday morning.
