Visibilities of 2.5 miles or less occur on about 10 to 13 days per month from October through March along the shore. From October through February, wave heights of 5 feet or more can be expected 10 to near 20 percent of the time and 10 feet or more up to 2 percent of the time. Extreme wave heights of 17 to 19 feet have been encountered. Since strong winds over a long fetch of water are conducive to creating rough seas, strong winds out of the E and W quadrants over Lake Ontario are often danger signals. Sea conditions are best from May through July when waves of less than 1 foot occur 50 percent or more of the time.
Thunderstorms can occur at any time, but are mostly a summertime problem.
They are most likely during the late afternoon. Over the open lake, thunderstorms are most likely during August when they occur about 2 percent of the time. The main part of Lake Ontario usually remains open throughout the winter, with only a few patches of thin ice and slush during cold spells. Its small area and great depth give Lake Ontario a large heat storage capacity. In addition, the land portion of the basin contributes more runoff to its lake than any of the other lakes.