Significant rime ice events in Utah's Wasatch Mountains: Impacts and conceptual models

A significant amount of research has been conducted on rime ice development and its impact on aviation safety. However, relatively limited research has been conducted on rime icing on terrestrial objects. Rime ice can be a significant source of water equivalent (i.e., up to 10% of the water content of the snowpack in portions of the Colorado Rockies), but it can also be a significant hazard. Heavy rime ice events can have an impact on the efficiency and integrity of equipment such as ski lifts and mountain trams. In addition, a rime crust on top of an unstable snowpack can contribute to increased avalanche danger.

During the winter of 2008-09' three significant rime ice events were reported in the Wasatch Mountains of northern Utah. These events impacted resource expenditure and equipment safety at area ski resorts. In addition, the events contributed to a dangerous snow pack that resulted in a significant avalanche cycle which resulted in several avalanche fatalities. All three events were associated with shallow cloud layers whose depth did not allow for heterogeneous nucleation to occur resulting in a cloud layer primarily comprised of super-cooled water. These super-cooled cloud droplets were then able to accrete on cold surfaces in the form of rime ice.

A brief review of rime ice processes and conceptual models will be presented. The three significant rime events from the 2008-09' winter will be investigated in detail. This will include the interrogation of observed soundings from nearby Salt Lake City, discussion of the microphysical processes at work, as well as the development of synoptic scale composites and conceptual models depicting the three events.