The clouds showed up very clearly in the sat images.....not sure what this article is talking about.
They were quite obvious.
That said, I did come to the conclusion a blanket ban was over-the-top.
There was plenty of free air in between the clouds. It basically came in waves, leaving lots of time they could have flown even avoiding all the ash.
Honestly, I am of the opinion better safe than have one accident, but it now looks like the blanket ban was a bit too much.
On 04/15 you could see a plume extending across the North Sea, north of Scotland, reaching as far as Norway. This plume was predicted to drift south across France and Germany. By the time it did this, it was invisible.
Plumes from subsequent eruptions were visible only within a few hundred miles of the volcano.
A question I have is this: How does the ash density over Europe during the flight ban compare to the ash density ( over Europe ) in the days following the 1980 Mount St. Helens eruption? The Mount St. Helens plume extended around the world, remember.
