A Rare Early Fall Case of Non-Tropical Tornadic Supercells in North Alabama.
Nadler, David ; Carcione, Brian ; Kula, Andy

The greatest potential for supercells across the Tennessee River Valley region occurs between March and May, with a secondary peak in November. Tornado-producing supercells are extremely rare during the early fall except for those associated with tropical cyclones. On 22 September 2006 several non-tropical tornadic supercells affected portions of northern and central Alabama causing moderate damage to homes, crops and vegetation. This event was driven by an unseasonably warm, moist air mass that rapidly spread across the region, coupled with favorable vertical shear profiles and locally backed winds at the surface. Initial forecast challenges for forecasters and numerical models included the identification of key mesoscale features and thermodynamic characteristics. However, situational awareness on the part of the National Weather Service, local media, and the public elevated quickly, allowing area meteorologists to provide more than adequate warning for the storms.

The use of remote sensing tools and techniques, real-time observations, and mesoscale modeling proved beneficial in improving situational awareness and identifying specific weather phenomena, especially prior to and during such significant weather events. Synoptic and mesoscale features, such as warm fronts, small-scale boundaries, the thermodynamic structure of the lowest layers of the atmosphere, and local terrain influences have been more accurately assessed. We will demonstrate certain local tools and techniques and their use in determining storm type and tornado potential for the 22 September 2006 case.