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What Is Thundersnow?

Snow falls over Horse Guards Parade on January 13, 2017 in London. The Met Office has issued a yellow "be aware" warning for much of the country. Image Credit: Chris J. Ratcliffe/Getty Images.

 
While the United States deals with its usual conga line of snow and ice storms that are a frequent visitor in the middle of winter, our closest ally across the pond found itself in the midst of an unusual situation: not only did parts of typically temperate Great Britain see a decent amount of snow this week, but the snow was accompanied by thunder. Parts of the United Kingdom experienced thundersnow as a potent winter storm brought heavy precipitation, blustery winds, and the threat of significant coastal flooding to Scotland and England.

A strong ripple in the jet stream allowed a low-pressure system to develop near Scotland and work its way down the eastern English coast late this week, bringing more than half a foot of snow to higher elevations of Scotland and coating areas as far south as London with a light dusting of snow. That doesn’t sound like much, but just like bigger cities in the United States, even a small amount of snow can cause mass chaos if it hits at the wrong time. The storm led to mass flight cancellations, snarled highway traffic, and even caused thousands of evacuations along the coast, where authorities worried that a storm surge—sea water pushed inland by strong winds—would inundate coastal communities.

But the adverse impacts of the snowstorm were overshadowed in news coverage by that 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.

The other process, known as forcing, is what caused the thundersnow in the United Kingdom this week. 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 U.S. East Coast 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.

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Weather Watch
It Just Snowed In the Sahara for the Second Time In Less Than a Month
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The town of Aïn Séfra, Algeria might need to find a new nickname. Though it’s often referred to as “The Gateway to the Sahara,” the 137-year-old province in northwest Algeria is currently digging out from a rare—and unexpected—snowstorm that left the desert town covered in several inches of snow and battling sub-zero temperatures.

While the Daily Mail reported that “locals took to the nearby sand dunes to enjoy the unusual weather,” the strangest part of the story is that this is Aïn Séfra’s second snowfall in less than a month. On Sunday, January 7, a freak blizzard left parts of the Sahara blanketed in as much as 16 inches of snow.

This most recent storm marked the region’s fourth snowfall in nearly 40 years; in addition to January's dose of the white stuff, the area has been hit with other surprise wintry events in February 1979 and December 2016.

But North Africa isn’t the only area that’s seeing record-breaking weather events. On Saturday, February 3, 17 inches of snow fell on Moscow within 24 hours in what the country has dubbed “the snowfall of the century.” In mid-January, Oymyakon, Russia—a rural village in the Yakutia region, which is already well known as one of the coldest inhabited areas of the world—saw temperatures drop to -88.6°F, making it chilly enough to both bust thermometers and freeze people’s eyelashes. And you thought dealing with single-digit temperatures was tough!

[h/t: Daily Mail]

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Weather Watch
Record-Breaking 17 Inches of Snow Covers Moscow in 24 Hours
Vasily Maximov, AFP/Getty Images
Vasily Maximov, AFP/Getty Images

Moscow sees some of the most brutal winters of any world capital, but even locals weren't prepared for the most recent winter storm to batter the city. As Newsweek reports, a record-breaking 17 inches of snow buried Moscow within 24 hours.

Roughly 7 inches of snow fell just on Saturday, February 3, and the deluge continued through the following Sunday. The accumulation has already been dubbed the "snowfall of the century," and officials expect up to 3 additional inches to cover the ground over the next three days.

The sudden blizzard has brought life to a stand-still in the metropolis of 12 million. The mayor is warning motorists to stay off the roads as around 15,000 snowplows clear the snow. About 2000 trees have been toppled by the storm, injuring at least five people and killing one.

Even as the worst of the weather winds down, over 40,000 people in Moscow and the surrounding regions are without power. Meanwhile, traveling in and out of the city has become close to impossible: Around 100 flights are grounded at the local airport indefinitely and at least 10 have been canceled all together.

The historic snowfall hasn't stopped many of Moscow's tougher residents from venturing outside. Check out photos from the event below.

Person cross-country skiing over snow in Moscow.
Yuri Kadobnov, AFP/Getty Images

Walking through a blizzard in Moscow.
Yuri Kadobnov, AFP/Getty Images

Walking through the snow in Moscow.
Yuri Kadobnov, AFP/Getty Images

Walking through the snow in Moscow.
Yuri Kadobnov, AFP/Getty Images

[h/t Newsweek]

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