What Is Thundersnow?

Jessica Kourkounis, Getty Images
Jessica Kourkounis, Getty Images

The northeastern United States is dealing with its second major nor'easter in a week, with rain and heavy snow—and the associated power outages—cutting a path across the Mid-Atlantic and New England. But news of the adverse impacts of the snowstorm is being accompanied by an unusual buzzword: thundersnow. Thundersnow occurs during a thunderstorm that produces snow instead of rain. The mechanisms that produce rainy thunderstorms and snowy thunderstorms are largely the same, even if the air temperature is below freezing.

A band of snow can become strong enough to produce lightning through two processes known as convection and forcing. Convection occurs when an area of warm air quickly rises through cooler air above it. Convective snow is most common during lake effect snow events like those you’d find on Lake Ontario or Lake Erie, since the process requires extreme vertical temperature gradients that can result from bitterly cold air flowing over a warm body of water.

Forcing is slightly different. A strengthening low-pressure system involves fast, dynamic changes in the atmosphere, especially when one of these storm systems quickly gains strength. Such a fast-developing storm can cause large amounts of lift in the atmosphere, a process that forces air to swiftly rise like you’d see during convection. This creates intense bands of snow that can grow so strong that they produce thunder and lightning. This process is responsible for the thundersnow that occurs during blizzards and nor’easters, those powerful storms that regularly hit the eastern coast of the U.S. during the winter. Thundersnow can be pretty exciting—just ask The Weather Channel's Jim Cantore:

The name “thundersnow” can be a bit misleading. One of the most enjoyable things about a snowfall is how silent it is outside when there’s a thick blanket of snow on the ground. Snow absorbs sound waves so efficiently that you can usually only hear ambient noises immediately around where you’re standing. Snow muffles the sound of thunder for the same reason. Thunder that might be audible for many miles during a rainy thunderstorm might only be audible for a few thousand feet away from where the lightning struck. Unless the lightning strikes very close to where you are, you might only see a bright flash during thundersnow without ever hearing the thunder.

While thundersnow is a fascinating phenomenon to encounter, it does involve lightning, after all, and it’s just as dangerous as any other lightning bolt you’d see in a rainy thunderstorm. If you’re ever lucky enough to experience thundersnow, the event is best enjoyed indoors and out of harm’s way.

This piece originally ran in 2017.

What is Lake-Effect Snow?

Tainar/iStock via Getty Images
Tainar/iStock via Getty Images

As you probably guessed, you need a lake to experience lake-effect snow. The primary factor in creating lake-effect snow is a temperature difference between the lake and the air above it. Because water has a high specific heat, it warms and cools much more slowly than the air around it. All summer, the sun heats the lake, which stays warm deep into autumn. When air temperatures dip, we get the necessary temperature difference for lake-effect snow.

As the cool air passes over the lake, moisture from the water evaporates and the air directly above the surface heats up. This warm, wet air rises and condenses, quickly forming heavy clouds. The rate of change in temperature as you move up through the air is known as the "lapse rate"; the greater the lapse rate, the more unstable a system is—and the more prone it is to create weather events.

Encountering the shore only exacerbates the situation. Increased friction causes the wind to slow down and clouds to "pile up" while hills and variable topography push air up even more dramatically, causing more cooling and more condensation.

The other major factors that determine the particulars of a lake-effect snowstorm are the orientation of the wind and the specific lake. Winds blowing along the length of a lake create greater "fetch," the area of water over which the wind blows, and thus more extreme storms like the one currently pummeling the Buffalo area. The constraints of the lake itself create stark boundaries between heavy snow and just a few flurries and literal walls of snow that advance onto the shore. The southern and eastern shores of the Great Lakes are considered "snow belts" because, with winds prevailing from the northwest, these areas tend to get hit the hardest.

The One-Day Record Snowfalls In Each State

Greenseas/iStock via Getty Images
Greenseas/iStock via Getty Images

Long after you’ve grown out of believing in magic, every thick, whirling snowstorm still seems to have been cast upon your town by a winter warlock (or Frozen’s resident ice queen, Elsa).

It’s also pretty magical when those inches of stacked snowflakes add up to a message from your manager telling you not to come into the office. In southern states like Georgia or Florida, sometimes all it takes is a light dusting.

But even those characteristically balmy places have hosted some serious snowstorms over the years, and David Cusick for House Method crunched the numbers to find out which ones made the record books. Using data from the National Centers for Environmental Information, Cusick created a map showing the one-day record snowfall for each state.

Florida finished in last place with a scant total of 4 inches, which occurred in Santa Rosa County on March 6, 1954. About two years before that, on January 14, 1952, Colorado had a staggering 76 inches—that’s more than 3 inches per hour—a national record that’s remained unchallenged for nearly 70 years.

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But other states have come close. The snowstorm that hit Colorado in 1952 wreaked almost as much havoc in California, whose record from the same day was 75 inches. And Washington saw 70 inches of snow in November 1955, beating its 52-inch record from 1935 by a full 18 inches.

Though Midwestern states have gained a reputation for harsh, snowy winters, their one-day record snowfalls are surprisingly moderate. The Illinois and Indiana records are 24 and 26 inches, respectively, both slightly lower than Ohio’s 30-inch snow day from 1901. In 1993, North Carolina bested Ohio’s record by 6 inches.

Wondering how your individual county’s record compares to the overall state one? Cusick created a map for that, too, which you can explore below.

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[h/t House Method]

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