A low-light visible/near-infra-red satellite image of the Ross Ice Shelf area at 15 10 UTC on 1 November 1986 showed a cloud-free region along the Transantarctic Mountains from the Liv Glacier northward. The corresponding thermal infra-red image indicated that the clear area was a katabatic air mass, fed by katabatic winds blowing from the main glacier valleys that dissect the Transantarctic Mountains. The cloud-free area broadened to the north and its western edge passed just to the east of Minna Bluff. The katabatic air mass crossed the edge of the Ross Ice Shelf, extended about 350 km offshore and developed cloud streets. Thus, this katabatic airstream appeared to propagate horizontally for over 1300 km. Analyses are presented of its association with the regional atmospheric circulation, of its time evolution and of its probable impact on the sea ice cover over the Ross Sea. Aspects of the governing dynamics are discussed.