What is onion snow?

Onion snow is a colloquial term used in some regions of the United States to describe a late-season snowfall that occurs after the onions have been planted but before they have fully matured. It is named that way because it typically happens around the same time when onion bulbs start to peek out from the ground. Onion snow usually happens in the months of April or May, when temperatures are warming up enough to encourage early plants. It can be a nuisance for farmers and gardeners who are eager to start their growing season, but it is generally considered a harmless event. In some regions, onion snow is also referred to as "sugar snow" or "sap snow", as it often coincides with the time of year when maple sap is collected for syrup making.