I recall that there wasn't any natural snow anywhere at the Winter Olympics in South Korea in 2018.

300 mm of rain in 24 hours is a huge amount. Average annual precipitation where I live is 637.7 mm.

The lake effect not only moderates the temperature extremes but it can result in massive snow dumps when cold air freezes the water vapor emerging from the lakes. It's more likely to happen on the eastern shores of the large lakes but any locality near the shores is susceptible. Keweenaw Peninsula in Upper Michigan is the snowiest place in the Great Lakes region.

If it winds from the east-southeast, Helsinki may experience what is called the St. Petersburg snow machine early in the winter. After the Gulf of Finland freezes over that does not happen.

An acquaintance of mine lives in Missisauga. He wrote in his blog that he experienced +27 C and -10 C within a single week in one March about 20 years ago.