"Light volcanic ashfall can be anticipated downwind of Tongariro", it said, potentially affecting the Waikato, Hawkes Bay, Gisborne and Bay of Plenty areas.
Christian Raymond Brown, 40, from Kirton-in-Lindsey, sustained serious head injuries in the fall near Ash Grove Farm on the A631 at North Willingham, on 12 February.
It is less useful for ash which has yet to fall and instead is distributed, in clumps and layers, at various altitudes and thus in different wind conditions through a large patch of atmosphere.