Semantic differences with dense and concentrated.
The latest ash is more dense - which is a good thing - being heavier it drops out more quickly. One of the problems with the early ash was it was very light and remained in the upper atmosphere.
In the last few days large amounts of the ash have been injected much higher into the atmosphere - more into the regions aircraft fly.
Tomorrow's flightpaths are either above the ash (above 35,000' or FL350) or around to the south.
They can be seen on
Jeppeson if you select
North Atlantic High Lvl Sig. (EB) or
North Atlantic High Lvl Sig. (WB) from the middle of the menu.