During the early morning hours of 2 May 2006, a complex of thunderstorms moved from southern Illinois into southern Indiana and central Kentucky. Marginally severe weather was expected overnight, though surface-based instability was expected to diminish with eastward extent into the early morning hours of 2 May. However, as the complex of thunderstorms with embedded bowing segments moved into the more stable environment in central Kentucky, damaging surface winds still occurred, as well as an F-0 (EF-0) tornado around 0830 UTC (430 am EDT).

It is often assumed by operational forecasters that surface-based thunderstorms more often occur during daylight hours or peak mixing hours as opposed to overnight. In principle, it can often be a safe assumption that boundary-layer stability increases overnight during the typical minimum mixing hours. Contrary to expectations, the atmosphere in this case became more unstable as the night progressed, allowing for the damaging surface winds and weak tornado to occur.

Although this may have been an atypical scenario, nocturnal events have in the past produced severe weather in supposed stable boundary-layer environments. Operational forecasters need to use all available data from which to best analyze the near-storm environment, and ACARS (Aircraft Communications Addressing and Reporting System) data can provide such support. It will be shown that the ACARS upper-air sounding data proved vital during the early morning hours of the 2 May 2006 event.