A westward propagating roll cloud and cool change on Tasmania’s north coast

On 1 March 1997 a recreational pilot reported flying under and in front of a roll cloud on the northern Tasmanian coastline. This roll cloud, which was accompanied by a marked wind change at the surface, was propagating westward along the northern Tasmanian coastline, rather than in the easterly direction usual for cool change passage in the mid-latitudes. This paper describes the synoptic environment in which the roll cloud formed, and using mesoscale numerical weather prediction (NWP) simulations of the event shows that the roll cloud was associated with a gravity-current-like structure that developed after a cool change had surged northward along the Tasmanian east coast, and which has much of the character of the better-known Southerly Burster (or Southerly Buster) of the New South Wales coastline. It is argued that there is the potential for such events to occur on any day when a dry cool change surges northward along Tasmania’s east coast, and several other events are documented.