 If the ridge is too far away or too weak, the east winds around the high are inadequate to bring tropical moisture into the mountains of Mexico and southwest U.S.However, if the ridge sets up in a few key locations, widespread and potentially severe thunderstorms can develop.Unlike the Pacific region of the United States and the west coast of Baja California, precipitation in the North American monsoon is not associated with large-scale mid-latitude cyclones, but with thunderstorms which have very different spatial/temporal distribution characteristics.