A gravity wave forms when crests and troughs align in the upper levels, interacting with the atmosphere and the ocean. An undular bore is a gravity wave where the frontal boundary bumps and lifts a shallow layer of air at the surface. With these confusing items noted, flying over the Gulf of Mexico may be safer. Weatherwise Magazine reports there were no methods of predicting these predominantly springtime events but now can be predicted in advance. Once gravity yanks the layer of air to the surface it creates smooth rolling waves; replicating rippling water after a pebble is tossed into a pond. Undular bores cause rapid, 180 degree vertical wind shifts in excess of 35 knots, causing severe thunderstorms. Forecasters can now assist pilots in avoiding these dangerous conditions.