Wednesday, February 25, 2009

Giant Hail..............

As we continue with severe weather awareness week today I will discuss large hail and the severe storms that have produced some of the largest hail on record. Hail is a type of precipitation which grows inside the thunderstorm due to strong updrafts suspending ice crystals in the storm cloud until they grow to a point where the updraft can no longer support them and they fall to the Earth. The largest know hail stone to strike the United States is in the photo below from a storm in Aurora, NE.

This hailstone is just over 7” in diameter and 18.75” in circumference. It was the largest stone in one piece from this storm however, there were reports of larger stones that broke apart on impact with the ground. In some places up 12” diameter creators were left on the ground. Below is a short movie of the volumetric radar return from the storm that produced this giant hail. What is amazing about this storm is not only the height, topping out over 61,000’, but the strong reflectivity near the top of the storm, 60dbz at nearly 46,000’.

Another powerful storm that produced very large hail was right here in East Texas last year when softball size hail was reported near Bullard on February 5th. Below is a short movie of the volumetric radar return from the storm that produced this giant hail. Notice the storm was nowhere near the height that produced the giant hail in Nebraska. This storm formed during the cool season so you do not need to have storms as high to produce very large hail because the mid levels of the atmosphere are much colder.

You can imagine that chunks of ice the size of softballs or larger can be very dangerous if caught outside. The last known death in the United States occurred in March of 2000 when a man in Lake Worth, TX was hit in the head by softball size hail. Now the Great Plains are known for very large hail at times but parts of south Asia and China are known for devastating hail storms. In July of 2002, 25 people lost their lives during a hail storm in the Henan Province of China. Bangladesh is also notorious for very large hail. In fact the heaviest hailstone on record fell there in April of 1986 and weighed just over 2.2 pounds. I have not seen the actual dimensions on this stone but I would have to imagine it would have been slightly larger than volleyball size.

So how can a storm suspend ice particles this size? It all has to do with the strength of the updraft. Once we start to see hailstones the size of softballs or larger, the storm’s updraft speed will exceed 100mph! This was the case back in October 2007 when a massive hail storm hit Santo Cristo, Brazil. In the photos you see stones over 10cm in diameter, or about the size of softballs.

So unlike with tornadoes, the United States is not the hail capital of the world. While we get our fair share, even here in East Texas, other parts of the world see this severe weather phenomenon as well. Large hail is commonly found along the front range of mountain chains with the storms along the Himalayas producing the most and largest hail on Earth.

1 comment:

John Barness said...

Thank you for the good article.