When what's being called the "Snowfall of the Century" hit Moscow over the weekend, authorities were forced to issue something highly unusual in the Russian capital: a snow day.

Just how rare is a snow day in Moscow? Well, it took over a month's worth of snow to fall in a 36-hour period – some spots of the capital reaching 22 inches deep – before school was canceled, the Meteorological Office told the Associated Press.

Over 150 flights in Moscow's three major airports were delayed due to the heavy snowfall, including an extra 16 incoming flights that needed to be diverted from Moscow runways, according to Sputnik News.

To aid the nearly 3,000 city workers in snow removal, authorities requested the help of the army to combat the snowfall left behind after back-to-back storms Russian meteorologists are calling the "Arctic Invasion", according to the Los Angeles Times.

City officials estimate it could take more than a week before all streets are cleared.