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What is a blizzard anyway?

A powerful winter storm may be heading toward New England. Whether or not the storm becomes a blizzard will depend on specific meteorological factors.

White out conditions on Newbury Street in Boston on Feb. 2015.Suzanne Kreiter/Globe Staff/file

It’s time to pull out your boots and snow shovels again. New England is preparing for what could be a powerful storm this weekend.

Forecasting models increasingly agree that from Friday night into Saturday evening, a foot or more of snow, fierce winds, and coastal flooding could slam the area. The weather system is expected to be pushed our way by the jet stream, a belt of strong winds running from west to east that directs and energizes weather systems. The stretch between Long Island and eastern Maine at the greatest risk.

Sounds like a blizzard, right? Maybe.

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What is a blizzard?

Though the term is thrown around colloquially, a storm has to meet specific meteorological criteria to qualify as a blizzard. According to the National Weather Service, a blizzard is a storm with large amounts of blowing or falling snow and winds greater than 35 miles per hour that combine to reduce visibility to a quarter of a mile or less for a minimum of three hours.

Winter storms are a yearly occurrence in these parts, but blizzards aren’t all that common. New England’s last blizzard occured in March 2018.

This weekend’s weather could meet those standards in some areas; meteorologists are predicting blustery conditions and as much as 2 inches of snowfall per hour. If things do get intense, some regions — especially eastern Massachusetts and Rhode Island — could experience their biggest snow events in four years.

Whether or not we see a blizzard will depend on the storm’s exact intensity and track, and on the interaction between the northern and southern branches of the jet stream.

Okay, so what’s a nor’easter?

As you’re tracking weather reports to see if a blizzard is on the way, you may see forecasters use another term: nor’easter.

Nor’easters are less specifically defined; they’re simply large areas of very low pressure that form storms off the East Coast. They can happen during any season, but are most common and acute between September and April. Their name comes from their origin — they’re usually caused by winds from the northeast.

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Nor’easters are far more common than blizzards, and sometimes bring heavy rains instead of snow. The downpours and power outages of October 2021 were caused by a nor’easter, as was the memorable snowstorm of December 2020.

Some other notable nor’easters to strike New England have been the Great White Blizzard of 1888, which dumped fifty inches of snow on parts of Massachusetts; the infamous Blizzard of ′78, which brought two feet of snow to the area and didn’t stop for 33 hours; and the ”Snowmageddon” that pummelled Boston in January and February 2015, the National Weather Service said.

This weekend will probably put another nor’easter in the books.

What on Earth is bombogenesis?

Perhaps the most ominous sounding expression you’ll hear in weather reports this week is “bomb cyclone.”

The term refers to storms that have undergone bombogenesis, which means they have experienced a steep drop in atmospheric pressure (at least 24 millibars, if you want to get technical about it) over a 24-hour period, and therefore intensified rapidly.

The term bombogenesis was coined in 1980 by the late Massachusetts Institute of Technology professor of meteorology Frederick Sanders. He used the word — as well as the even scarier synonym “explosive cyclogenesis” — to describe explosively strengthening winter storms. In recent years, many in New England have become familiar with the term. A Massachusetts storm went through bombogenesis just this past October.

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How is climate change impacting all of this?

Again, snow storms are a hallmark of New England winters. But climate change is changing how these weather systems work and how intense they get.

Overall, amid the climate crisis, studies show that New England and Massachusetts are experiencing higher temperatures and less snow, simply because winters are trending shorter and average temperatures are getting higher. Last year, for instance, Boston saw both its warmest year and warmest winter on record.

However, data also show that though snow is falling less frequently, nor’easters, blizzards, and other storms may also be getting more intense due to other shifting climatic factors. And yes, bomb cyclones may occur more frequently.

The Gulf of Maine, for instance, is among the fastest-warming bodies of water on the planet. In fact, earlier this month, one research group announced that inlet waters beside Maine and northern Massachusetts experienced record heat in recent months.

These high Gulf temperatures contribute to overall warming in New England. But aquatic heat can also fuel storms, which suck up heat energy from warm surface water, creating moisture in the air that can fall as rain or snow.

Material from prior Globe stories was used in this report.


Dharna Noor can be reached at dharna.noor@globe.com. Follow her on Twitter @dharnanoor.