There’s a “snow emergency” declaration in effect, but somehow that doesn’t quite convey the enormity of Erie’s Christmas Day storm.

It began at 8 p.m. on Christmas Eve and continued nearly nonstop through the next day. As of Tuesday morning, it was still snowing in the city of around 100,000 in far northwest Pennsylvania. In the 30 hours, Erie had 53 inches of snow on the ground, which shattered records across the entire state of Pennsylvania.

It is the largest 2-day snow total in the state, beating out the 44 inches that fell in Morgantown in 1958.

Even though this storm has occurred over the course of less than two days, the amount of snow that has fallen in that time also breaks the record for the most snow in 13 days, which used to be 52.8 inches.

In other words, over the past two days, Erie has received more snow than it has ever seen over the course of two weeks.

The area around the Great Lakes is one of the few places in the world where such extraordinary snowfall totals are possible. You can count on one hand the number of times New York City has received more than 53 inches of snow in an entire winter. The average winter snowfall in Erie is about 100 inches — a far cry from, say, Washington, D.C., where the average winter snowfall is a comparatively paltry 15 inches.

Very specific weather conditions come in line for this to happen. To put it simply, lake effect snow occurs when cold air passes over relatively warm lake water, picks up some of that moisture from the lake and transports it to land, where it falls as snow. The biggest lake effect snow storms tend to happen in November and early December, when water temperatures are still pretty mild. A big cold snap can convert that warm moisture into a lot of snow — and fast.

Well no gym today for you. Although that shoveling is probably a better work out. Erie snow! Wow

Posted by Jourdan Lagace on Tuesday, December 26, 2017

When heat and moisture are transferred to the air, they create a layer in the atmosphere that is very unstable. The air in this layer — because it is so warm and moist, and therefore less dense than the surrounding cold air — rises rapidly. The moisture condenses and forms snow, and the winds carry the band of snow downstream where it falls over land.

When a band of lake effect snow really gets going, an interesting thing happens. Air rises in the snowy regions and then sinks on either side, which means the area right next to these snow bands can be completely clear, with blue sky and sun. It also means just a few miles can separate 53 inches from zero.

With the Christmas storm, Erie’s snowfall so far this month is 92 inches — about 8 inches short of its annual average total. Assuming it can pick up another 4 inches between now and Sunday, Erie will also break a more significant Pennsylvania record: most snow in the entire month of December.