Wind and Waves

Storms and Storm Surges

The storm systems that cross the Great Lakes Basin are spawned primarily from the collision of two air masses. A frontal boundary along the path of the high altitude jet stream separates relatively cool, dry air originating in Canada from warm moist air originating over the Gulf of Mexico (during the winter season) and over the Eastern Pacific during the other three seasons. Along this frontal boundary, low and high-pressure systems are steered by the jet stream flow from west to east.

As storm winds blow across many miles of open water on the Great Lakes , they drag some water towards the downwind side of the lakes. This causes a temporary rise in water level along the downwind shore and a lowering of water on the upwind shore.

The temporary rise in water level is called a storm surge, storm set-up, or storm-induced rise (Figure 1). The drop in water level is a set-down. Set downs are sometimes a problem for vessel navigation and for recreational boats tied to piers. Storm surges occur on all of the Great Lakes shorelines. Similar, but shorter, periodic oscillations of lake levels are called seiches. Seiches are caused by rapid changes in air pressure or rapid shifts in wind direction as weather systems pass over the lakes.

Wave Development

As the wind blows across the surfaces of the lakes, energy is transferred from the wind to the sea surface. Most of this energy generates currents. The rest builds waves (Figure 2). Although the wind energy that goes into wave creation is a small percentage of the total energy transferred from wind to water, it is an enormous quantity of energy.

Wave conditions vary greatly over time at deep-water locations on the Great Lakes . One minute, the lake is "flat calm". Within the hour there may be waves two feet high. Seven hours later, the waves may be seventeen feet high.