Recently, a late-season severe weather episode occured in the fall in mid Octoberwell after the transition season had ended. During the early morning hours and continuing well into the afternoon of 18 October 2005, long-lived severe supercells were noted across northern Arizona. Damage surveys conducted over the following days indicated that at least two tornadoes, as well as large hail, occurred across northern Arizona.
A deep closed low approached the southwest United States in the days proceeding the severe weather episode. With the approach of the low, deep layer shear increased significantly. Buoyant instability, as measured by the Lifted Index and CAPE, indicated that the atmosphere was only marginally unstable.
In this paper, we examine the background environmental conditions that supported the development of long lived supercells and, additionally, how the local environment may have augmented necessary ingredients for the development of supercells and severe weather.