 Substantial height falls—implying cooling in the mid layers of the atmosphere—coupled with the sharpening trough allowed for strong divergence to overspread the highest risk area.At the surface, a deepening area of low pressure initially centered near the Texas–Oklahoma border early on January 21 deepened and accelerated eastward, reaching the Arkansas–Missouri border during the overnight hours.A dry line extended southward across eastern Texas, providing increased mechanisms for rising air as it combined with a cold front and pushed eastward into Arkansas.