Check out the thin lines of reflectivity moving northward on this radar loop from about 415 pm through 655 pm. They appear to be gravity waves, as they are moving at speeds close to 70 mph, faster than the low-level wind flow. It would be like making waves in a river moving downstream…the waves would move faster than the river.
There is one in NW Alabama around 545 pm that may have caused a spinup of the storm near Haleyville, and there are three moving through the BHM area now. If they are gravity waves, the reflectivity on radar is being caused by upward motion causing condensation of water in clouds or even light rain.
