During the Surface Heat Budget of the Arctic (SHEBA) measurement program from October 1997-October 1998, extensive measurements of the surface energy budget, the boundary layer structure,and cloud cover have been obtained during the entire annual cycle over the Arctic pack ice in the Beaufort Sea. During the winter months, frequent large transitions in the near surface temperature occurs despite the lack of solar insolation and in the presence of a nearly continuous low-level inversion. These transitions appear to be forced by the arrival or disappearance of low-level clouds. Using the surface and boundary layer turbulent flux data from the main camp 20-m tower,the longwave radiometric flux data from Eppley radiometers, cloud data from a cloud radar and a lidar, and raw insonde data, this presentation will show the statistical characteristics of these events and explore the evolution of the lower tropospheric structure during one or several of these events with temporal resolutions down to minutes