Seiches

Strong winds or sudden changes in barometric pressure over different sections of the Lake can cause the surface of the Lake to literally tilt, piling up water against one shore and causing a corresponding drop on the opposite shore. This storm-induced tilting can be up to three feet high on Lake Michigan. When the storm abates, the tilt oscillates back and forth across the Lake for a long time before it is dampened by friction. This back and forth oscillation, kind of like water sloshing in a bathtub, is called a seiche. The time for a seiche to complete one back and forth oscillation can be from 30 minutes to several hours. Usually there is some kind of seiche action happening on the Lake, although it is usually only about several inches in amplitude. Sometimes, people confuse seiche action with tides. Although lunar forces act on Lake Michigan's waters the same as they do on the oceans, because of its relatively small size, tides are almost imperceptible--only a fraction of an inch.

According to the National Oceanic Service, a seiche is a phenomenon that occurs in large bodies of water when strong winds and rapid changes in atmospheric pressure push water from one end of a body of water to the other.