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Climate

The lake has a natural seiche rhythm of eleven minutes. The seiche effect normally is only about 3 ⁄ 4 inch (1.9 cm) but can be greatly amplified by earth movement, winds, and atmospheric pressure changes. Because of its great depth, the lake as a whole does not completely freeze in winter, but an ice sheet covering between 10% and 90% of the lake area typically develops, depending on the severity of the winter. Ice sheets typically form along the shoreline and in slack water bays, where the lake is not as deep. During the winters of 1877 and 1878, the ice sheet coverage was up to 95–100% of the lake. During the War of 1812, the ice cover was stable enough the American naval commander stationed at Sackets Harbor feared a British attack from Kingston, over the ice. The lake has completely frozen over on five recorded occasions: in 1830, 1874, 1893, 1912, and 1934.

When the cold winds of winter pass over the warmer water of the lake, they pick up moisture and drop it as lake-effect snow. Since the prevailing winter winds are from the northwest, the southern and southeastern shoreline of the lake is referred to as the snowbelt. In some winters, the area between Oswego and Pulaski may receive twenty or more feet (600 cm) of snowfall. Also impacted by lake-effect snow is the Tug Hill Plateau, an area of elevated land about 20 miles (32 km) east of Lake Ontario. The "Hill", as it is often referred to, typically receives more snow than any other region in the eastern United States. As a result, Tug Hill is a popular location for winter enthusiasts, such as snow-mobilers and cross-country skiers. Lake-effect snow often extends inland as far as Syracuse, with that city often recording the most winter snowfall accumulation of any large city in the United States. Other cities in the world receive more snow annually, such as Quebec City, which averages 135 inches (340 cm), and Sapporo, Japan, which receives 250 inches (640 cm) each year and is often regarded as the snowiest city in the world.

Foggy conditions (particularly in fall) can be created by thermal contrasts and can be an impediment for recreational boaters. Lake breezes in spring tend to retard fruit bloom until the frost danger is past, and in the autumn delay the onset of fall frost, particularly on the south shore. Cool onshore winds also retard the early bloom of plants and flowers until later in the spring season, protecting them from possible frost damage. Such microclimatic effects have enabled tender fruit production in a continental climate, with the southwest shore supporting a major fruit-growing area. Apples, cherries, pears, plums, and peaches are grown in many commercial orchards around Rochester. Between Stoney Creek and Niagara-on-the-Lake on the Niagara Peninsula is a major fruit-growing and wine-making area. The wine-growing region extends over the international border into Niagara and Orleans counties in New York. Apple varieties that tolerate a more extreme climate are grown on the lake's north shore, around Cobourg.