National Weather Service meteorologist Scott Truett said the heavy "thundersnow" resulted from an unstable air mass, much like a thunderstorm.

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"Thundersnow" accompanied the winter storm in parts of Kansas and Missouri, which National Weather Service meteorologist Scott Truett said is the result of an unstable air mass, much like a thunderstorm.

NPR: Winter Storm Blankets Great Plains With Snow

In a car with no air bags and an unstable body structure, a driver's biggest danger is the steering wheel.

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It is cheaper to develop air transport to remote, geologically unstable areas, than to build and maintain roads.

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Unstable means that if an imaginary balloon filled with air from near the ground were to be lifted upward, colliding with some weather feature such as a cold front, the "balloon" would become warmer than the surrounding air at that level.

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