I think I can only remember a few instances in my life where I’ve encountered hail, and I suppose that makes me fortunate, as being pelted with ice rocks from the sky doesn’t sound like the most appealing way to be one with mother earth.
In any case, my lack of hail experience probably comes form the fact that I’ve spent most of my life in coastal California. But I still wonder, how does hail form?
“Here’s a quarter so you can see how large my hand is, and then see how small these hailstones are.”
A bit of research (on Wikipedia) will tell us that snow forms when a cloud is below freezing, and decides to rain. That’s simple enough. Hail on the other hand is formed when there are significant updrafts within a cloud. Updrafts are typically found in thunderstorm clouds.
Our other condition for hail is supercooled water droplets. Now this is getting cool, or, interesting.
A supercooled liquid refers to the state when a liquid is below its freezing temperature, but has not formed into a solid. Ice formation requires seed crystal nuclei, which can be anything from the glass on the side of your cup to dust particles floating in the air. High in the atmosphere, there is usually a lack of seed nuclei (no, nitrogen atoms etc are not acceptable). Basically, the crystal needs something to form around. If not, you can just keep cooling down the water to lower and lower temperatures.
Incidentally, it is also possible to superheat liquids past their boiling point, as the boiling process also requires a finite amount of energy to being the formation of air bubbles within the liquid. Of course, both supercooling and superheating are possible by simply changing the pressure of the liquid in question, lowering or raising the freezing or boiling points, respectively.
Ruining this incredible phenomenom is the water itself! Rain that forms at the bottom of the cloud can be swept into the updraft, and it can smash into the supercooled water at speed of 5 billion miles per hour, immediately forming a layer of ice around it. Subsequently, as our little hail pellet rises, it accumulates more and more layers of frozen water, growing and growing until…
Which inevitably grows too heavy to be supported by the updraft, leading to:
And the outcome of such an onslaught is:
Anyways, its snowing here in new york.