Bomb cyclones and polar vortexes—winter’s scary weather explained

An intense winter storm with
hurricane-force winds is expected to hit the Midwest on Wednesday.
The bomb cyclone follows an active winter season where polar vortex
winds created dangerous conditions throughout parts of the
U.S.

It’s not the first time these conditions
have hit the country.

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

We answer your questions here.

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^[1], 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^[2] reported in 2018 that
states in the path of this current bomb cyclone experienced
hurricane-force winds, heavy snow, and flooding.

Winds spinning around the Arctic circle can push intensely cold
air south.

The vortex is a mass 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.

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.”

A Nor’easter is geographically constrained cyclone driven by
Atlantic winds. They occur anywhere from New England to Georgia but
aren’t seen in other parts of the country.

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^[3].

"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.

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.

"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."