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Alaska Got 15 Inches of Snow in 90 Minutes Last Week

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Alaska is obviously no stranger to snow, but this month's white weather will likely go down in the state's record books. As The Weather Channel reports, Thompson Pass—a 2805-foot-high area in Alaska’s Chugach Mountains—received a whopping 15 inches of powder in just 90 minutes on Wednesday, December 6.

Thompson Pass sits just outside of Valdez, a tiny port city on Alaska’s south coast. Located along the Gulf of Alaska, Valdez is perhaps best known for the infamous 1989 Exxon Valdez oil spill, and for its rich Gold Rush history. Today, it’s important for commerce, since it’s the northernmost ice-free port in North America. But ice-free doesn't mean blizzard-free: The city is regularly cited as one of the snowiest places in the U.S., if not the snowiest. On average, locals can expect to see (and smell) 300 or more inches of frozen precipitation per year. As for Thompson Pass, it very often receives more than 700 inches of the wet stuff in a year.

Still, Mother Nature truly outdid herself on December 6, when Thompson Pass was slammed with what weather historian Christopher Burt deemed to be one of modern history’s most intense snowfalls. By the storm’s end, 40 inches of heavy snow had accumulated in just 12 hours, according to The Washington Post.

Who angered the winter weather gods? Or, more scientifically speaking, which atmospheric conditions led to the storm? According to experts, a stream of warm water vapor from the Pacific Ocean hit Alaska’s coast, traveling through an aerial channel known as an “atmospheric river.” When atmospheric rivers hit land, they release this water vapor as either rain or snow, according to the National Oceanic and Atmospheric Administration.

Intensifying the phenomenon was the North American Winter Dipole, which The Washington Post’s Jason Samenow described as a “fancy term to describe abnormally warm conditions in the West and cold conditions in the East.”

"Under such a pattern, the jet stream, the super highway for storms that divides cold and warm air, surges north in the western half of the nation, and crashes south in the eastern half,” Samenow said.

Valdez residents are accustomed to snow, but last week's storm was particularly challenging for townspeople. An avalanche buried Richardson Highway, the city’s only overland route that leads in and out of town. It reopened on Thursday, December 7, according to The Cordova Times, but driving conditions were poor.

While extreme, the Thompson Pass blizzard might not be history's weirdest snowfall. For example, arid countries like Kuwait and Iraq have experienced snow. In January 1887, 15-inch snowflakes were reportedly spotted at Montana’s Fort Keogh. And in 1921, over six feet of snow fell between April 14 and April 15 in Silver Lake, Colorado—the most snow to ever fall in a 24-hour period in the U.S.

[h/t The Weather Channel]

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Weather Watch
Thanks to Desert Dust, Eastern Europe Is Covered in Orange Snow
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Certain areas of Eastern Europe are starting to look a bit like Mars. Over the last few days, snowy places like Sochi, Russia have experienced an unusual snowfall that coated mountains in orange powder, according to the BBC.

The orange snow was the result of winds blowing sand from the Sahara east to places like Moldova, Romania, Bulgaria, Ukraine, and Russia. The sand mixes with precipitation to form orange-tinted snow. According to the BBC, the phenomenon occurs semi-regularly, turning snow orange about once every five years, but this year is especially sandy. As a result, skiers are navigating slopes that look like they're from a different world, as you can see in the video below from The Guardian.

The Sahara rarely gets snow, but when it does, the landscape can look somewhat similar, as you can see in this image of the Atlas mountains in Morocco.

Instagram is currently filled with photos and videos from Eastern Europe featuring the odd-looking snow. Check out a few samples below.

[h/t BBC]

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Weather Watch
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.

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