National Geographic News
The frozen mist from Niagara Falls coats the landscape around Prospect Point at Niagara Falls State Park.

Prospect Point at Niagara Falls State Park covered in snow after the polar vortex.


Angie McPherson

National Geographic

Published January 23, 2014

"Bombo"-what? Bombogenesis. It's not a word you expect to hear from your local meteorologist. So what is it exactly? And what's with the mishmash of strange weather vernacular over the past few months?

On Tuesday, meteorologist John Bolaris at was the first to use the term "bombogenesis" to describe the large, fast-moving snowstorm that was heading toward the East Coast. NPR journalist Mark Memmott noticed the unusual word and wrote his own article called "What Is This Bombogenesis And Why Is It Dumping Snow On Us?" Memmott's story went viral and brought national attention to the word.

But these two writers were not the first to use this term and other terms that have been popularized this winter.

The odd collection of weather words used in the media—such as "polar vortex"—are actually advanced technical terminologies for specific weather conditions. "Polar vortex" describes a wind pattern over the North and South Poles. "Bombogenesis" is a slang word used by meteorologists to describe a winter storm that forms quickly.

Why haven't we heard these words before? According to Chris Vaccaro, a spokesperson for the National Weather Service, meteorologists are using these terms to describe weather conditions in areas that don't typically see such events; the use of these words is then accelerated through social media.

"As a result of social media, these terms are picked up and spread much further," said Vaccaro. "Now there are more voices to amplify our weather words."

And even though an odd winter word may first make you go "huh?" it can then teach you about the way weather works. After a while we become more familiar with meteorology terms: "When I hear the term 'polar vortex,'" Vaccaro says, "I remember all of the characteristics I learned about it in school."

That being said, here are three winter weather terms that are particularly apropos this winter.

Polar Vortex

A polar vortex, also known as a circumpolar vortex, is a wind current that circulates above the North and South Poles. The currents sit like spinning hats above the Poles.

During the winter season, the northern polar vortex typically increases in strength as it is blanketed in 24 hours of darkness. Heat from the surface rises into the atmosphere and creates an area of low pressure above each Pole. The warm air becomes colder because of the lack of sunlight and is contained over the polar region by a jet stream.

When the jet stream—a result of colder air over the polar region pushing up against warmer air—is strong, the air stays trapped in the vortex above the polar region. But when the jet stream is weak, undulations or kinks in the jet stream cause polar air streams to travel farther south, an arm of cold air breaking out of an icy circle.

The polar vortex itself is nothing new. It has existed for many years, and "it will continue to be there," says Vaccaro. The term "has appeared in meteorologist glossaries dating back to at least the 1950s."

But this winter, the bitter winds from the polar vortex disrupted areas of the U.S., closing schools and offices in cities like Chicago. This southern dive may be a result of warmer temperatures in the Arctic region, which weaken the polar vortex.

Studies by the National Oceanic and Atmospheric Association (NOAA) suggest that a loss in Arctic sea ice has contributed to a weaker polar vortex, which then brings frigid air farther into North America and Europe, and warmer temperatures to the polar areas. (See related: "Behind Record U.S. Cold Snap: Canadian Air and a Jet Stream Kink.")


A photo of a man walking through snow.
A man walks through strong winds and blowing snow in Massachusetts.

Bombogenesis is meteorological slang that describes a rapidly developing storm system as noted by the raid fall of its central pressure. The word originates from "cyclogenesis." Bombogenesis is a form of cyclogenesis. "The so-called 'bomb' is when the barometric pressure drops sharply," said Vaccaro. The lower the barometric pressure, the stronger the storm.

This type of storm is common on the East Coast. For instance, many nor'easters are created through bombogenesis.

The term was popularized on Tuesday when the central pressure of a storm system over the Atlantic dropped sharply in 24 hours. An area of cold air from Canada encountered warm air from the Gulf Stream in the Atlantic to create a textbook example of bombogenesis.

The result was a snowstorm that battered quite a few major cities from Kentucky up to New England. The fast-moving system was so severe in the northeast that New York, New Jersey, and Delaware declared states of emergency. (See "Editor's Picks: Our Favorite Pictures of the Winter Snowstorm.")


A photo of water being dumped on a wildfire.
An air tanker drops water on a wildfire that was fanned by the Santa Ana winds, which are similar to williwaws.

"Williwaw" describes a violent windstorm created when gravity pulls high-density cold air down from a mountain to the sea. Williwaw is a colloquial word for a katabatic wind in Alaska, where the strong winds can be dangerous for local fishermen.

The origin of the word "williwaw" is unknown; the Oxford Dictionary dates the use of the word back to the middle of the 19th century. And if you want to impress your friends, you should also learn the term "katabatic winds." That's a term meteorologists use to describe gusts of wind associated with the buildup of dense air. And such winds aren't confined to cold areas.

Another famous katabatic wind is known as a Santa Ana, which blows over southern California in autumn and winter. Santa Anas are warm, dry winds created when air is compressed as it moves down a mountain range. These dry katabatic winds are associated with spreading wildfires.

Now to try using these new words in a sentence. (For other interesting meteorology terms, snoop around in the National Weather Service glossary.)

Follow Angie McPherson on Twitter.

Correction: An earlier version of this story incorrectly implied that both polar regions are blanketed in 24 hours of darkness. Only one polar region is dark while the other is light, this has been updated for clarity. It also stated that Santa Ana winds are foehn winds. They are actually classified as warm katabatic winds.

Charlene Carney
Charlene Carney

What I would like to know is how the Pacific Decadal Oscillation affects the Polar Vortex. Since the Vortex is run on warm air is the PDO causing it to swoop south or expand it's boarders to include the temperate zone? Right now 11/19/14 we have basically zero snow and 35-50 degree temps. What gives?

Bettye Gronskei
Bettye Gronskei

The snow scene is beyond beautiful.  Living in the South has its gorgeous days too.  

Christopher Willsey
Christopher Willsey

Thermodynamic Jet-Stream Climate Indicator Theory. Published in 2012.

William Lehman
William Lehman

Williwaws in the Pacific Northwest are not a "winter thing" we get them especially in the summer. The wind coming down off the mountains right on the shore are dangerous as hell to sailboats in the San Juans, and to anyone tenting in alpine valleys.  A sudden wind out of a clear blue sky at speeds to 50 kts is enough to cause a knock down to a sail boat and I have watched dome tents and their inhabitants get unstaked and rolled until someone catches them and stops them or they fetch up against something hard, usually at speed.  We've had 10'x20' wall tents lifted over tree tops.

Toni Marie
Toni Marie

This is an interesting winter for sure.

Yoysy Olivero
Yoysy Olivero

Muy Interesante. Agregar Palabras Nuevas A Nuestro Argot Popular. Gracias.

Malcom Bennett
Malcom Bennett

we learn something new every day in fact 3 things just now

Kirsty Hameleers
Kirsty Hameleers

National Geographic, you should be more specific about something else in this article!

When you talk about the polar vortex and how it originates, you talk about how the 'polar regions are blanketed in 24 hours of darkness'. During the winter in North America and Europe this is true for the North Pole (aka the Arctic). But during winter on the northern hemispere it is summer on the southern hemisphere. That means that the South Pole (aka Antarctica) is experiencing 24 hours of daylight; not really good conditions for a polar vortex according to this article.

Keep a sharp eye out for this kind of formulations and what they actually mean! Two (so far noted) mistakes in one article is a lot for you NatGeo! :(

Marek Lahoda
Marek Lahoda

Nice article and thanks for new slang terms :-) But hey, this is National Geographic, don't mix up katabatic winds with foehns! These two phenomenons form totally differently!

Katabatic wind: cooling of air in the mountains due to longwave radiation (emission), the air gets denser and therefore flows down the mountain (slope, glacier, ...)

Foehn (Chinook and many other names): weather phenomenon which occurs when air crosses a mountain barrier and it rains-out itself (loses its moisture), it's warmer behind the mountain because of different adiabatic lapse rates of moist and dry air ... see:

Roz Blt
Roz Blt

Very interesting, and useful information! Thank you Angie :)

Jenny Sonjon
Jenny Sonjon

fascinating, wish my memory was good enough to remember them.

Angie McPherson
Angie McPherson

@William Lehman Williwaws are incredible. I had never heard of them before I wrote this article. I'd like to follow them this year to learn more about their impact to local areas. Very interesting wind and thank you for sharing your first-hand insight. 

Angie McPherson
Angie McPherson

@Kirsty Hameleers Hello Kirsty, you are completely right. I didn't specify that one polar region is 24-hours of darkness while the other is not (this article was edited and lost some of this explanation). But the polar vortex does exist semi-permanently in both hemispheres. In the winter, it is stronger in the northern hemisphere. I'll go ahead and clarify that in the copy now. Thank you so much for reading. I appreciate your comments. 

Angie McPherson
Angie McPherson

@Marek Lahoda Thanks Marek, I appreciate the fully formed definitions. I realize the two winds are created differently. But foehns are a type of katabatic wind. Since the Santa Ana is a foehn wind, I thought it was a perfect link. Next time I'll be sure to define both separately so readers can see how the two are different as well as related. Thank you so much for reading and enjoy your new slang words :)

Marek Lahoda
Marek Lahoda

Thanks for your response Angie. Unfortunately I have to insist on my statement, because foehns are not a type of katabatic wind. They are two different things. It's like you said that bus is type of car. Both are road vehicles and they have the same features - transporting people, but it's not the same thing. Likewise with the winds - both are going down the hill. Foehns are always warm, katabatic winds can be both warm and cold. Santa Ana is a warm katabatic wind. But to cite Wiki: "Note that while the Santa Ana Winds are a katabatic wind, they are not a Föhn wind. A Föhn wind results from precipitation on the windward side of a mountain range which releases latent heat into the atmosphere which is then warmer on the leeward side (e.g., the Chinook or the original Föhn). The Santa Ana winds do not originate in precipitation, but in the bone-dry high deserts." Though Wiki is not the most relevant source of information they have this right. At least according to that what I learned in my meteorology classes... In fact it's just a matter of classification and doesn't matter so much, but since you are the voice of us, scientists, getting the information to the people, please be specific about this :-) Thank you, I'll be looking forward to your next article! :-)


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