Earlier this week as severe thunderstorms roiled Southern New England, videos and photos quickly sprang up on social media showing hailstones, big and small, pelting the region. Dime-sized. Quarter-sized. Nearly golf-ball proportions. The sudden deluge of these chunks of ice caught many New Englanders by surprise.
So what is hail exactly?
Hail basically comprises small balls of frozen rain that have grown larger depending on a thunderstorm’s strength.
Mostly a summertime form of precipitation, hail forms when raindrops get pulled high enough into a thunderstorm cloud in the cold areas of the upper atmosphere and then accumulate supercooled water that in turn freezes. The more water, the larger the hail.
Huge hailstones measuring 4 to 5 inches wide — basically the size of a grapefruit and DVD — have been known to fall across parts of the Midwest and Great Plains.
Why do some storms produce large hail while others don’t?
The answer lies in the strength and speed of the updraft, or rather a rising column of air. A thunderstorm has many components and the more robust types of thunderstorms, called supercell storms, not only can produce hail, but they’re also responsible for generating most of the tornadoes in the United States.
The updraft can be so powerful — reaching wind speeds over 100 miles per hour — that it can create a rain-free zone because the raindrops can’t get down to the ground; they’re actually being blown skyward.
There’s a lot of activity going on in the highest regions of a thunderstorm. Supercooled water, which is actually liquid water below 32 degrees, water and pieces of ice are all colliding.
Depending on how strong the updraft is, the hailstones can continue to grow and reach not only damaging but deadly sizes in the most powerful of thunderstorms.
Updrafts can get quite strong in some storms. It’s no wonder a raindrop can get carried far up to form this most interesting type of precipitation. Wind speeds range from 24 mph to produce pea-sized hail to 98 to 103 mph for grapefruit- and softball-sized hail, respectively.
Depending on how cold it is in the upper atmosphere storms can create either cloudy or clear hail. If the ice forms rapidly, then the air bubbles stay intact and that’s when you get the cloudy ice called “dry growth.” Supercooled water that spreads across a little ice nucleus and freezes slower allows the air bubbles to escape, leaving the ice clear — this is “wet growth” hail.
Hail in New England
Our thunderstorms, even our largest ones, typically don’t develop the type of structure conducive for sustained updrafts with enough speed to generate the largest of hailstones.
Also, unlike some of the more mountainous regions of the country, the distance from the ground to the freezing level during the summer when thunderstorms are occurring is a lot higher, meaning the hail has plenty of time to melt before reaching the ground.
Which states see the most hail?
Although Florida has the most thunderstorms in the United States, places like New Mexico, Colorado and Wyoming have the most hail storms because the freezing layer is closer to the ground whereas in Florida the freezing layer is very high so it’s harder for the hail to even form.
