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 once were no methods of predicting these predominantly springtime events, but now they 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 today can help pilots avoid these dangerous conditions. Fastcast: Stuffy.