The climate of the Great Lakes-St. Lawrence River Basin has several distinguishing characteristics. Perhaps the two most important climatic elements affecting water resources in the basin are temperature and precipitation. Precipitation is ample, with significant amounts occurring year-round. Overall, the basin can be described as having warm summers and cold winters.
Several factors control the climate of the basin.
The sun is the primary source of energy for virtually all weather phenomena and in large part determines the absolute values of temperature and seasonal variations. Land masses respond much more quickly to changes in solar input than do large water bodies such as oceans. Therefore, seasonal air temperature changes tend to be larger in the interiors of continents than on coastal locations. Thus, the location of the basin in the interior of the North American continent contributes to large seasonal air temperature changes. Although the Atlantic Ocean is not located far from the eastern edge of the basin, it cannot exert a significant moderating influence because of the prevailing westerly air flow.