Bomb Cyclones and Polar Vortexes

What's behind the record-shattering cold heading towards the Northern Hemisphere?

It was already mind-numbingly cold in the U.S.—and then it got even colder. And if recent forecasts are correct, we haven't seen the worst of it yet.

It's so cold Niagara Falls has partially frozen. Record lows in some regions may be shattered in the coming days as a string of weather patterns with intimidating names hits the U.S. East Coast.

Bomb cyclones, polar vortexes, and arctic air masses are expected to blanket the region. New England is expecting hurricane-force winds, Maine and Boston had blizzard warnings as of Wednesday, and it's snowing in Florida.

Are these atmospheric conditions as scary as their names make them sound? And are they normal?

We answer your questions here.

People walk through a frigid Manhattan on December 28, 2017 in New York City. Temperatures are expected to reach record lows on Friday and into the weekend. PHOTOGRAPH BY SPENCER PLATT, GETTY IMAGES

What is a bomb cyclone?

It's called a cyclone, a bomb cyclone, or a cyclone bomb. Or a weather bomb. Or bombogenesis.

What is technically a "midlatitude cyclone" refers to when a storm gains strength from an extreme drop in atmospheric pressure. The effect is prompted by what is technically called "explosive cyclogenesis," and occurs when a storm drops by at least 24 millibars (a unit that measures pressure) in 24 hours.

According to the National Oceanic and Atmospheric Administration's website, a bomb cyclone occurs when a "cold air mass collides with a warm air mass." Cold arctic air colliding with warm ocean water is a common source of this collision.
After pressure plummets, air rushes in to fill the space between these two air masses, creating intense winds and strengthening the storm.

Despite the intense name, bomb cyclones are fairly common, particularly in northern Atlantic regions.
The National Weather Service predicts that states in the path of this current bomb cyclone will experience hurricane-force winds, heavy snow, and flooding.


What is a polar vortex?

The storm will unload what Washington Post meteorologist Jason Samenow describes as a "mother lode of numbing cold."
This will be thanks to chilling Arctic air from what's called the polar vortex.

The vortex is a swirl of cold air that sits over the Arctic region. It's full of swirling eddies that, during winter months, can grow and extend farther south. It represents the boundary of cold, polar air and warmer subtropical temperatures.

As National Snow and Ice Data Center Director Mark Serreze described for a video made by non-profit Earth Vision Trust in 2014, polar vortexes are bordered by the "polar front jet stream" that's constantly shifting.

A polar vortex outbreak in farther southern latitudes can have damaging impacts on regions' transportation and agriculture practices, and scientists aren't quite sure how these outbreaks will be influenced by climate change, says Serreze.
"The weather machine is going to respond to that," he said in the video. "Just how, we don't quite know yet."

Is this storm different from a regular Nor'Easter?

Not really. What's happening now is just way more intense.

In an interview with Vox, meteorologist Ed Vallee noted this week's storm would be the first Nor'easter of the year and larger—spanning from Maine to Florida—than normal.

The term Nor'easter simply refers to a midlatitude winter storm. Many Nor'easters form when that same polar jet stream collides with warm currents from the Gulf jet stream.

This collision facilitates winter storms like bomb cyclones, notes meteorologist for Weather Underground Bob Henson.
"Any areas that lose power due to heavy snow and strong winds will be vulnerable to intense cold," says Henson, making conditions more dangerous for people at risk.

What role does climate change play in all this?

It's well known that climate change can influence weather. The effect is known to exacerbate natural disasters like hurricanes and wildfires, and warming Arctic regions may even be making U.S. winters colder.
But linking one specific extreme weather event to climate change is tricky.

Henson notes that these types of multi-latitude storms vary greatly year-to-year, saying, "There are some indications these storms have become stronger and more frequent across the Northern Hemisphere in the last 60 years, but there isn't strong evidence of any major change in impacts along the U.S. East Coast."

"What we simply have here is a strong trough in what we call the atmospheric longwave pattern, or, as some might say, there has been a strong southward excursion of the polar vortex," said Serezze in a recent email to National Geographic.

Simply put: "It is winter. This happens."

When scientists talk about weather, they're referring to day-to-day changes, and when they discuss changes to the Earth's climate, they're referring to changes over time.

While the U.S. has experienced longer-than-normal cold weather this winter, meteorologist Eric Holthaus told National Geographic in a previous article that it's too soon to link this year's winter weather conditions to overall climate change.

"It's really difficult to say for certain if this exact weather pattern today would have happened the same way without climate change," he said. Though he added, "It's really irresponsible to say that climate change is not affecting weather everywhere on Earth."

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