What Makes a Blizzard 'Textbook'?
The meteorologist who wrote the book on northeast snowstorms says this system looks like “the big one.”
Despite the Weather Channel’s best efforts, we still don’t name winter storms like we name hurricanes.
This means that, while tropical cyclones tend to get remembered by their monikers (Ivan, Sandy, Katrina), snowstorms either get a quirky nickname or take on the weight of their whole year. “Snowmaggedon.” The Great Blizzard of 1996. The President’s Day snowstorm of 2003.
Well, watch out: Here comes the Blizzard of 2016. This weekend, a snowstorm equal to those historic gales is expected to wallop the mid-Atlantic states, dumping record-breaking levels of snow across the I-95 corridor. A weather model run on Thursday morning says that Washington, D.C could be headed for two-and-a-half feet of snow, a devastating amount of precipitation for the city. Towns along the East Coast shore, meanwhile, could face flooding and a hurricane-like storm surge.
And this forecast has pretty much been the word since Sunday, when all the major weather models came into concord about the size and import of the storm.
“The potential snowfall distribution has similarities to several major East Coast storms in [the] recent past,” wrote Paul Kocin, the winter-weather expert at the National Weather Service, in a forecast discussion. “The mechanisms coming together for a major snowfall are textbook.”
Kocin isn’t the only one who’s noted how similar this storm looks to historic blizzards. But his line attracted notice from many, including The Washington Post and Slate, because, well, in addition to being the former winter-weather expert at the Weather Channel, Kocin literally wrote the book about northeast snowstorms. His two-volume tome is titled Northeast Snowstorms.
(Kocin’s co-author for that work, by the way, was Louis Uccellini, the current director of the National Weather Service. The pair also developed the main classification system for giant northeast snowstorms.)
Kocin laughed when I asked him about the line on Wednesday. “I had about a half an hour to write that discussion,” he told me. “I don’t know who reads that!”
I wanted to know: What makes this storm textbook? Why did this system look so much like huge historical storms, and less like any other kind of winter weather pattern?
“First of all, there aren’t many [big snowstorms],” he said. “So there are certain things we look for when we’re looking for what appears to be the ‘Big One.’ And this one has the makings of the ‘Big One’ in just sort of the way it’s being set up.”
He described two important steps in the evolution of this set-up. The first came into place earlier this week. In this step, a cold, high-pressure system sits north of New York or over New England, while a low-pressure system develops over the middle of the country. In forecaster parlance, this second system over the middle of the continent is a “digging trough”: a big low-pressure system that’s rapidly getting bigger.
Then comes the second step. That low-pressure system moves toward the southeast and keeps getting bigger. Eventually, it hits the warm water of the ocean and starts working its way up the southern coast, toward the mid-Atlantic. But the high, cold pressure north of New York doesn’t move.
“The area of high pressure kind of sits where it is, while the low pressure area moves north and gets more intense,” Kocin said. “As it does so, the difference in pressure between the two systems draws a tremendous amount of moisture in. We see those in the maps. And it starts to create all sorts of precipitation with the cold air.”
He added that this mix of northbound low systems up the coast, and stagnant high-pressure systems over New England, isn’t uncommon. The forces involved in this storm are just very strong. “It’s just a very big manifestation of what we see all the time,” he said. “It looks like a classic Big One.”
These kinds of messy, disorganized systems are very different from hurricanes, the other type of major storms that Americans on the East Coast have to stay attuned to. Tropical cyclones draw their energy from warm water, he said. But nor’easters and other storms that develop inland work off a different mechanism. They emerge from differences in temperature.
“In winter it gets very cold, but the water temperature remains very mild. What the storm does is draw a very narrow boundary between the cold and warm air, where there’s a very big difference [in temperature],” Kocin told me.“Storm systems just love that temperature contrast. The bigger the temperature contrast, sometimes the bigger the storm.”
Despite the great confidence in this forecast, he cautioned that we couldn’t be absolutely sure until the snow comes down. “We still have two days before the first flake comes down,” he said. “The reality is—and this is an important last point—it hasn’t happened yet.”
“‘How accurate are your forecasts?’ We don’t know!”