Now, the first thing you should know about a bomb cyclone is it’s just a name—and unlike a sharknado, it’s not a literal one. The very real scientific term describes a storm that suddenly intensifies following a rapid drop in atmospheric pressure. Bombing out, or “bombogenesis,” is when a cyclone’s central pressure drops 24 millibars or more in 24 hours, bringing furious winds that can quickly create blizzard conditions and coastal flooding.

It’s actually not that rare a phenomenon; meteorologists estimate these kinds of storms break out in the Northern Hemisphere about 10 times a year. They can go by other names, like Nor’easter and mid-latitude cyclone, which may explain why you’ve never heard of one before Winter Storm Grayson started dumping snow in Tallahassee on Wednesday morning. But Grayson isn’t your typical bombogenerator.

It’s what happens when everything comes together just right (or just wrong). Grayson is expected to explode up the East Coast between now and Friday, intensifying as it makes its way from Florida to Nova Scotia, blowing record snowfalls around at category 3 hurricane wind speeds. “This storm is a synoptic meteorologist’s dream,” says Paul Huttner, who watches the weather for Minnesota Public Radio. “It’s a perfect alignment of the three things we look for.”

The first is a warm conveyor belt of tropical moisture, which the Gulf Stream is shuttling out of the Caribbean and right up the Atlantic coast. That’s pretty normal for this time of year. What’s less normal is the huge subzero air mass that dipped down from the Arctic about 10 days ago, plunging the Great Lakes and Eastern US into a sustained deep freeze.

Every year, around this time, the sun stops shining above the Arctic circle. No radiation means no heat, which means all that air gets real cold real quick. Most of the time, jet streams—the easterly flowing air currents near the upper reaches of the atmosphere—keep that cold air bottled up in the Arctic. But sometimes, upper air waves shift, forcing a buckle in the jet stream and allowing all that air to spill southward.

“The coldest air on the planet just happened to slide over Northeast America,” says Huttner. “And with this incredible moisture feed we’ve now got a huge temperature contrast. By the time this thing gets up into New England we’re talking about a good 100 degrees of temperature contrast across the center of the storm. And generally speaking, the stronger the temperature contrast, the deeper the storm.”