It's blizzard time on the East Coast. Thanks to an incoming nor'easter, Boston and New York are bracing for 1 to 3 feet of snow. The National Weather Service has issued a blizzard warning for some 29 million people. Officials are urging people not to drive in whiteout conditions.
So how often does this happen?
Meteorologist Devin Boyer made this fascinating map showing data on blizzard warnings around the United States between 2005 and 2015. Brighter colors indicate multiple warnings. As you can see, warnings happen a lot in the Midwest. But the Northeast still gets its fair share, particularly on the coast:
Blizzard warnings in the US, 2005-2015
The National Weather Service has a precise definition for what constitutes a blizzard — it occurs when there's lots of snow, very strong winds of at least 35 miles per hour, and visibility of less than one-quarter of a mile for at least three hours.
The combination of snow and wind is what's crucial here: the flurries of snow can create whiteout conditions that make it dangerous to drive. And those strong gusts can create severe wind chill. By contrast, if there's only snow or only wind, then the NWS will instead just issue a "heavy snow warning" or "heavy storm warning."
Historically, the upper Midwest and Great Plains have gotten the most blizzards by far, as cold air from Canada sweeps down and clashes with warm/moist air coming up from the Southwest and Gulf of Mexico, creating low-pressure storms. This dynamic helps create a lot of tornados in the spring — which is why this area is known as "Tornado Alley." But in the winter, it could reasonably be called "Blizzard Alley":
Number of blizzards, 1959-2000
In fact, it was Iowans who first used the term "blizzard" in its modern-day sense. Back in the 1870s, a local newspaper deployed it to describe a storm that dropped 16 inches of snow. Before then, the word was mainly used either as a boxing term to mean a volley of punches or to describe cannon fire.
Given all that, don't be surprised to find Midwesterners scoffing at worried East Coasters who have been ransacking Whole Foods to prepare.
The Northeast, for its part, doesn't tend to see strong winds and snow quite as often — unless, that is, there's a nor'easter storm ripping up the Atlantic coast. (Blizzards typically form on the northwest side of severe storms, where the gradient between the low-pressure storm and the higher pressure to the west creates intense winds.) That's what happened when New York City got blasted with record snow 2006. And it's what's happening now.
Blizzards can even pop up in places you'd never expect. Here's the NWS: "Northern Arizona can experience blizzard conditions when a strong low pressure system moves across southern Arizona and high pressure builds strongly into the Great Basin." (This is extremely rare, though, since there aren't a lot of strong low pressure systems moving across the state.)