Observations of Low Level Thermodynamic and Wind Shear Profiles on Significant Tornado Days

Research since the mid to late 1990s, has contributed to a more robust understanding of meteorological environments supportive of tornadic supercell thunderstorms (e.g., Rasmussen and Blanchard 1998; Evans and Doswell, 2002). Considerable effort has been given to identifying environments on tornado “outbreak” days, when it is common for several long-lived supercells to produce cyclic tornadoes that are often long tracked and intense (e.g., Thompson and Edwards 2000). Research from field experiments and post analysis of many significant tornado (i.e. ≥F2 on the Fujita scale) events indicates that two atmospheric conditions in particular have emerged as being critically important in environments supportive of significant tornadoes. Those two conditions are strong low-level wind shear and moderate to high values of low-level absolute moisture and relative humidity (Markowski and Straka 2000; Markowski et al. 2002; Nordin et al. 2003). This has also been supported by numerical modeling simulations (e.g., Wicker, 1996). All of this suggests, rather strongly, that much of the tornado process, or at least processes related to supercell tornadogenesis and maintenance, seems to happen at the lowest levels of the atmosphere, generally ≤ 1 km AGL.