Subsequent cloud formations, if present, are nearly always turbulent and often appear only in the form of scattered lines of irregular cumulus. Despite their ominous appearance, they seldom produce measurable precipitation, but are almost always accompanied by a short-lived, but often intense, wind squall near the surface which may be a potentially serious wind shear hazard for aircraft. Morning Glories propagate on average with speeds of about 40 kilometres per hour, but occasionally are observed to travel at speeds of over 60 kilometres per hour. Morning Glories tend to occur on a daily basis at Burketown over periods ranging from three to seven days in succession. Solitary Waves Morning Glory roll cloud formations are visible manifestations of largeamplitude solitary waves.
Solitary waves are somewhat unusual in that they occur as singular waves with one isolated crest.
Waves of this type propagate as exceptionally long-lived disturbances in waveguides created by stable layers in the lower atmosphere. A feature of larger-amplitude solitary waves is the region of trapped recirculating cooler air in the interior of the wave which may be transported by the wave over considerable distances. Solitary waves occur commonly throughout much of the arid interior of the Australian continent and elsewhere. Waves in inland areas almost invariably occur without cloud as clear-air disturbances accompanied by a sudden wind squall at the surface and a temporary increase in surface pressure. When sufficient moisture is present near the surface, as is often the case over the southern Gulf of Carpentaria region, large amplitude waves of this type may be accompanied by what appears to be a propagating roll cloud formation.