The fire covers an estimate 10 hectares next to the Fort George firing range in the Highlands.
The warning is in place across west, north-east, east and central Scotland until Saturday.
The A9 was closed after the Scottish Fire and Rescue Service was alerted to an out-of-control fire shortly before 2pm on Wednesday, March 17.
Emergency services were called to the scene near Portgower, Sutherland, at around 12.30pm on Saturday.
Firefighters are tackling multiple blazes across the Western Isles.
The blaze broke out in forestry near Bannockburn around mid-afternoon on Friday.
Three appliances were mobilised after multiple calls received about a wildfire visible across many parts of Glasgow.