Many carry the misconception that ice as a weather event can only occur during the winter months. While generally true, a certain set of circumstances can cause ice to fall from the sky even at very warm temperatures. This is known as "hail."
What is Hail?
Like sleet in the winter, hail is at its simplest a frozen ball of liquid. However, its formation is different. While sleet begins its life as a snowflake in the clouds, melting as it falls to the surface and then refreezing before it reaches the ground, hail is different.
Hail will also start as frozen, but quickly melts as it falls through the cloud. Before it exits the cloud, winds blowing back up into the clouds ("updrafts") blow the raindrop back up into the cloud where it freezes again, and gains more moisture before it . This process can repeat several times in the severest of storm, increasing the size of the hailstone.
This is why a hailstone when broken apart has layers like an onion -- that is the evidence of this process. Soon the hailstone becomes too heavy for the updraft to carry it back up into the cloud, and this is when it falls to the ground.
Where Does Hail Occur Most often in the US and Canada?
Like tornadoes, there is a region of the North American continent where hail is most commonly found. In the United States, this area extends from the area where Colorado, Nebraska and Wyoming meet south and east through the High Plains and into Oklahoma and Texas.
Across Canada, hail falls frequently during the summer months across the Province of Alberta, especially in the portion east of the Rocky Mountains. Weather expert Bryan Neaton of The Weather Network adds that all of these areas share a common thread of being downwind of large mountain ranges.
Thus, across the world, it could be expected that hail producing thunderstorms could also be found east of large mountain ranges where cold and warm air frequently intersect.
How Big Can Hailstones Get?
As the method for creating hailstones detailed above suggests, it takes very strong thunderstorms to produce large hailstones. These hailstones typically range from the size of peas to as big as softballs. Occasionally however, hailstones can grow much larger.
The world's biggest hailstone occurred in Aurora, Nebraska in June 2003. and measured seven inches across. It's size could be compared to that of a cantaloupe, and it was estimated that the stone hit the ground at a speed of 100 miles per hour.
Sources:
" Hail," Rene Munoz, UCAR. Last updated April 10, 2000.
"Hail Alley," Bryan Neaton, The Weather Notebook. August 27, 2004.
"Largest Hailstone in US History Found." National Geographic News, August 4, 2003.
