Brandi Simons/Getty Images
Brandi Simons/Getty Images

Why the Weather on the Great Plains Is So Extreme

Brandi Simons/Getty Images
Brandi Simons/Getty Images

It can be tough to live on the Great Plains. The flat terrain gives way to breathtaking views of both land and sky, but the smooth, fertile land is both good fortune and a curse when it comes to the weather. Whether it's an enormous thunderstorm or a ferocious blizzard, there's rarely a dull day when it comes to weather in the middle of the country. Just what is it about the central United States that makes the weather there so extreme?

The unique geography that makes this part of the country so grand is what exposes it to some of the most extreme weather nature can produce. The Plains are bounded by the Rocky Mountains to the west, the Canadian Prairies to the north, and the Gulf of Mexico to the south. The tall, jagged mountains of the Rockies act like an atmospheric dam, forcing hot air from the south and cold air from the north to pool up over the Plains. This helps to trigger some of the most interesting weather in the world.

Most major weather events around the world are set in motion by jet streams, which are fast-moving currents of air that wrap around the planet. Straight, rigid jet streams don't result in much interesting weather, but things can get wild when the jet stream grows wavy. Sharp dips in the jet stream, called troughs, can cause low-pressure systems to develop at the surface.

When these troughs clear the Rocky Mountains in the western U.S., diverging winds in the upper atmosphere cause air to rise from the surface, leading to the development of a low-pressure system over the Plains. These lows can be the size of a single state or sprawl across the entire country from north to south. We see these storm systems most often during the winter and spring, when the jet stream is most active over the United States.

The flat land acts like an expressway, helping these fledgling low-pressure systems draw enormous amounts of tropical air from the south and, during the winter, extremely cold air from deep in the Arctic. The lack of natural obstacles allows this air to flow toward storm systems virtually unimpeded, which can lead to explosive thunderstorms during the warm months and powerful and bone-chilling blizzards during the winter.

This atmospheric expressway doesn't stop at precipitation; it's also why the central Plains can have brutal heat waves and bitter cold snaps. It's not uncommon for areas in the north-central United States to struggle to climb above 0°F for days at a time during the dead of winter, and it's similarly common for places like Oklahoma and Texas to see temperatures above 100°F for a week or longer during the summer's worst heat.

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Britain Is in the Midst of a Rare ‘Wind Drought’
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Generating renewable energy in Britain is a little less than a breeze these days: A “wind drought” is halting the country’s wind turbines.

This month’s wind energy output is down 40 percent from the same time last year, New Scientist reports. On average, about 15 percent of Britain’s electricity comes from wind power. Data starting from July 1 of this year put the monthly average closer to 6.9 percent. Last month, turbines were producing less than 2 percent of Britain’s electricity—the lowest output in two years.

That’s with even more wind turbines being installed over the course of the past year, New Scientist says. The data aren’t entirely surprising, though. The jet stream tends to make the UK’s weather drier and calmer during the summer and wetter and stormier during the winter. But the high pressure the jet stream has brought with it this year has been unusually prolonged, scientists say.

“It’s like a lid, it keeps everything still,” UK Met Office spokesperson Grahame Madge told New Scientist. “From the forecast looking out over the next couple of weeks, there doesn’t seem to be any significant change on the way.”

The wind drought shouldn’t cause too many problems in the short term. Electricity demand is low during the summer (very few British homes have air conditioning), and the country’s been able to compensate for the lack of wind by burning more natural gas. If the wind drought continues to persist, though, UK residents may begin to see an increase in utility fees. Natural gas prices have already risen with the increased demand.

“As we continue to transition to a low-carbon energy system, managing the intermittency of renewable power an important role in balancing supply and demand,” a National Grid spokesperson told New Scientist. “However, we have planned for these changes and [are] ready to play our part.”

The wind drought comes about eight years after British politicians vowed to reduce the UK's dependence on fossil fuels. Last year was the first year that electricity generated from low-carbon energy sources like solar power, wind power, and nuclear power outpaced high-carbon energy sources like coal and natural gas. This summer’s wind drought may make it difficult to improve on last year’s numbers.

[h/t New Scientist]

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Why Does the Sky Look Green Before a Tornado?
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A common bit of folklore from tornado-prone parts of the U.S. says that when the skies start taking on an emerald hue, it's time to run inside. But why do tornadoes tend to spawn green skies in the first place? As SciShow's Michael Aranda explains, the answer has to do with the way water droplets reflect the colors of the light spectrum.

During the day, the sky is usually blue because the shorter, bluer end of the light spectrum bounces off air molecules better than than redder, longer-wavelength light. Conditions change during the sunset (and sunrise), when sunlight has to travel through more air, and when storms are forming, which means there are more water droplets around.

Tornadoes forming later in the day, around sunset, do a great job of reflecting the green part of the light spectrum that's usually hidden in a sunset because of the water droplets in the clouds, which bounce green light into our eyes. But that doesn't necessarily mean a twister is coming—it could just mean a lot of rain is in the forecast. Either way, heading inside is probably a good idea.

For the full details on how water and light conspire to turn the sky green before a storm, check out the SciShow video below.

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