New York City's extreme heat created this stormy, apocalyptic cloudscape

Dark stormclouds descended on New York City Tuesday afternoon.
Summer thunderstorms are fueled by hot, humid conditions that push more warm air up into the atmosphere, where it brews moisture and builds an unstable environment, creating the perfect recipe for a big storm.
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Around 2 p.m. on Tuesday, New York City descended into a cloud of darkness.

The skies opened up, thunder rained down, and lightning flashed across the sky.

Photojournalist Gary Hershorn snapped this image from Hoboken, New Jersey, across the Hudson river from Manhattan:

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It's all prompted by the sweltering temperatures that have been bathing the New York City region in sticky heat.

On Tuesday, New York declared a heat advisory would be in effect until 6 p.m., and the city opened up emergency cooling centers, as temperatures topped out at 86 degrees Fahrenheit in Central Park, with the humidity hovering near 70%. When it's that hot, the steamy surface of the Earth heats up, and all that air has nowhere to go but up.

As more of the warm air hits the cold above, it mixes in and cools off, forming water droplets and creating a moving cell. Cooler air, in turn, falls down into the atmosphere and continues mixing with the heat, creating a perfectly dynamic system for a thunderstorm to thrive on: a mix of moisture and unstable air.

The phenomenon can be even more pronounced over cities like New York, which are laden with dark, hot asphalt and big black buildings, creating heat islands.

Scientists predict that the worst summer storms are only going to get more violent as the planet warms.So far, they've been right.

As peoplecreate pollutants, those greenhouse gases trap more of the sun's heat, which raises the planet's temperature.

Increased precipitation is a side effect of that process: the hotter the atmosphere gets, the easier it is for evaporation to occur on the surface of the Earth. Warmer air can also hold more water, which prompts heavier rains and more summer floods. Take a look at how much wetter the wettest storms in the US have gotten since 1958: