Tornadic Events During UNSTABLE: Use of Supplemental Soundings

The Rocky Mountain foothills in Alberta, Canada are a common location for thunderstorm initiation. However, the mesoscale physical mechanisms involved are not well understood, mainly due to the lack of observational data in the region. This severely limits Environment Canada forecasters' ability to issue timely and accurate severe weather alerts for the large growing population in this area of Canada. The Understanding Severe Thunderstorms and Alberta Boundary Layers Experiment (UNSTABLE) was a field project in summer 2008 undertaken to better understand the large-scale and mesoscale forcings of summer storms, including drylines, convergent boundaries, and land surface variations, to name a few. The sparse operational observing network was supplemented with various instruments including four radiosonde sites, mesonet, mobile vehicles, remote sensing instruments and an aircraft. On July 7th and 15th, 2008, tornadic thunderstorms tracked through the southern periphery of the UNSTABLE domain. Upper-air measurements from the supplemental UNSTABLE field instrumentation were evaluated against the pre-existing operational upper-air network. It was found that the mobile UNSTABLE soundings were able to better capture the storm environment, leading to better characterization of the available instability and shear profiles that lead to tornadic development. This suggests that supplemental soundings (on an as-needed basis) are valuable for forecasting operations in this region.