Lake Erie has an effect on the surrounding weather at all times of the year, not just winter. Our "lake effect" seasons can be broken down into meso-climates that have a profound influence on weather and life in the vicinity of the lake. Essentially there are two lake effect seasons.
The "Stable Season" (shown under the yellow bar) is defined as the time of the year when the lake temperature is cooler than the overiding air temperature. As shown on the chart, this covers the period from roughly early March through late July. During that time of the year the cooler water of the lake acts as a stabilizing influence which suppresses the growth of clouds and can decrease the severity of convective weather events such as severe thunderstorms. The cool lake also acts as a natural air conditioner of sorts. In fact, Lake Erie is one of the main reasons that Buffalo, NY has such beautiful summers. Skies are normally sunnier during the summer than in many other parts of the country, and the temperatures are very comfortable. Buffalo has never officially had a temperature above 100 degrees!
The "Unstable Season" is the time of the year that most people equate to "lake effect". By late summer the water temperature actually becomes warmer than the air temperature, especially at night. Late August often brings on nocturnal shower activity that develops due to the lake. As the air temperature continues to cool during early Fall, we begin to see the development of lake effect rain showers. They develop just like lake effect snows and produce very localized heavy amounts of rain. In fact, in September of 1996 a lake effect rainstorm actually produced flooding across the northern suburbs of Buffalo. Finally, by the end of October, the air cools enough to produce snowfall, and the lake effect snow season begins. On relatively shallow lakes such as Lake Erie, significant ice cover develops as the winter progresses and by the end of January the lake freezes over, drastically reducing lake effect snow. However, on deep lakes such as Ontario, widepsread ice cover rarely develops, allowing lake snows to continue unabted throughout the winter.