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Name: Tina
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Question:
I teach preschool and would like to be able to answer these questions for future weather units. In a recent storm I noticed that the hailstones were tear drop or triangular shaped. I don't remember seeing such a shape before. Can you tell me about the shape? Why it is different?


Replies:
Hi Tina

In upper regions of clouds, air temperatures are below 32 degrees Fahrenheit and water freezes. The shape the water freezes in forms the shape of hailstones. So irregular shaped hailstones are more the rule than the exception. And then as they fall to earth, and sometimes get sucked back up into the cloud by uplifting winds, they may add more layers of ice adding to the irregular shapes.

Sincere regards,

Mike Stewart


Tina,

How the hail is oriented/tumbles as it falls and the forces of the wind upon it determine its final shape. Teardrop shapes are common, as are half spheres with one side (the side that is up while it falls) "scooped out". Hail can form a tear drop shape when it falls without being tumbled or blown sideways by wind (in still air). Air moving past the hail stone as it falls causes water that is encountered to move upwards along the hail (water streams out from the top), resulting in a tear drop shape.

The triangular shape may be just an oddity of how the wind spun the hail around as it was falling.

David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory


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