As much as an additional 250 centimetres of heavy, sopping snowfall was forecast to collect on the ground in the Buffalo and western New York area by the end of Thursday. The day before, the city was buried under 170 centimetres.
Even for a city that knows winter wallops, that’s significant, according to Environment Canada's senior climatologist David Phillips.
"This week, we saw a year’s worth of snow in the Buffalo area, so they got a real workout," he said, noting that the average annual snowfall for Buffalo is 245 centimetres.
So what’s so different about the latest round of squalls? It helps to understand some of the environmental conditions that fuel it.
What is lake-effect snow?
For one thing, it’s not really a storm system that dumped all this white stuff, said CBC meteorologist Jay Scotland.
Rather, it’s more of a weather phenomenon that occurs when very dense, cold air pushes across warmer water, in this case Lake Erie, forming steam clouds as the air overloads with moisture.
There’s also a magic number at play.
"If the air temperature is at least 13 degrees cooler than the water temperature of those prevailing winds, the result is that the moisture is picked up off the lake…and then released as heavy snow," Scotland explained.
"It’s heavy, wet snow because it’s ‘warm snow,’" he said.
As of Thursday afternoon, surface temperatures at some areas of Lake Erie were over 7 C, with the temperatures of prevailing winds around –13 C. Scotland said that the wider that temperature gap, the more intense the lake effect.
What else is needed for the lake effect to happen?
Phillips likens it to baking a cake. Aside from the at least 13-degree Celsius temperature difference between water and prevailing winds, there are some other key ingredients.
"You have to have the right winds, in the right direction," Phillips said. "If they’re quite variable, you won’t get the lake effects streamers, but just a little dusting of snow."
The combination ofcold, dry air across an open lake, and long, steady and strong winds are to blame for what’s happening in Buffalo.
In lake-effect conditions, winds are almost "locked" into a particular path, "almost as if you grease the skids and the air just flows in the same direction, speed and orientation and it just builds up and snows," Phillips said.
So why was the lake effect so intense in Buffalo?
The long expanse of Lake Erie has something to do with it, as well as its east-to-west orientation, Scotland said.
"The longer the distance of warm water that the air is travelling across, the heavier and more intense the snow will be," he said.
Climatologists and geographers refer to this overwater distance as a fetch. The longer the fetch, the more moisture it collects to fuel more intense snow bands.
As it happens, Buffalo is on the eastern tip of Lake Erie. Scotland said that means the cold air, acting like a sponge, soaks up more water vapour over the lake and then cools down once it reaches the shore to release a massive dump of snow.
"You have that long, expansive lake lined up perfectly with cold wind, and that’s what we’re seeing in Lake Erie and Buffalo. It’s a very pronounced situation," Scotland said.
The lake effect has been so dramatic that at least eight deaths in western New York have been blamed on the snow, mostly from people suffering cardiac arrest while shovelling out driveways.
Although the final numbers aren’t in yet, Phillips said climatologists are anticipating a possible U.S. record for snowfall during a 24-hour period.
How are the driving conditions in these squalls?
Motoring through a lake-effect snow event can alternate between periods of blustery white-knuckle driving interspersed with clear periods of blue skies, then back to a wall of blizzard-like conditions again just a few kilometres down the road.
"All of a sudden you can't see the hood ornament on your car and it's just blowing and drifting and coming at you, then you come out of it again," Phillips said.
These narrow bands of lake-effect snows are very common.
Scotland pointed out that while the polar blast swept southern Buffalo, it was relatively calm and sunny to the north.
"It’s highly localized, but it’s actually quite easy to understand," he said. "If you were to spray a garden hose on your lawn, is it your entire garden getting soaked? Or just the part of it that’s under the spray? This is literally like a hose shooting snow on top of you."
Is the lake effect all bad news, then?
Not if you’re a skier, apparently. A solid dose of lake-effect snow is actually welcomed by some ski resort operators, who see dollar signs when the rest of us see white.
"There have been some recreational areas built up because of the snow, so it’s not necessarily the curse or evil that everybody presents it to be," Phillips said.
Some resorts in the past have been able to open earlier than planned due to abundant lake-effect snow.
Phillips said the lake effect typically lasts from November through January, and then peters out in February as the lakes begin to cool off and ice over, cutting off moisture to the air.