An Analysis of Northward-Moving Tornadoes within an Open Warm Sector Across Eastern Texas

Tornadoes in eastern Texas generally track to the east as predominant westerly upper flow acts on their parent storms. However, an examination of tornadoes from 2000 to 2018 finds that 22% of all tornadoes in the region move in much more northward directions. These tornadoes' parent storms develop in the open warm sector prior to the arrival of a main linear forcing mechanism (e.g., front, dryline). In fact, some of the more notable tornado outbreaks in recent years across Texas have occurred from northward-moving thunderstorms. This bifurcation of storm/tornado motions is important to understand for forecasting, warning, and messaging of these events. The results show these tornadoes typically occur eastward of large, slow moving, mid to upper-level long-wave troughs and underneath the left quadrant exit-region of an upper-level jet streak. The composite pattern also shows that a low-level jet in eastern Texas, a surface low centered in west-central Texas, and a warm/stationary front extending northeast of the surface low were common for these events. The typical air mass was indicative of weak instability, low convective inhibition, and high shear. Radar analysis of the northerly moving, tornadic storms showed mesocyclonic circulations with smaller diameters and lower rotational shear when compared with tornadic storms that moved in an easterly direction.