Orographic Middle and High Cloud
This cloud often forms east of New Zealand’s main mountain ranges as a result
of an increasing northwest flow ahead of a frontal system. At first, single Ac
lentics form, but as the front approaches, upper level moisture increases and an
‘arch cloud’ develops. This arch cloud usually displays a very sharp western edge.
Flying conditions within the arch are usually smooth; however, conditions will be
very turbulent below the cloud at low levels. Moderate or severe icing may be
encountered within the arch depending on its thickness.
with respect to Peter Fisher