Dime-sized hail fell from the sky in parts of the North Valley today as snow blanketed higher elevations. Since hail storms are rare here, let’s answer the obvious question: What causes big hail like that?
One big hint: Did you hear the simultaneous thunder?
Hail forms when a thunderstorm’s violent updrafts carry raindrops rapidly upward, where they freeze into little balls, or when already supercooled water drops freeze on contact with tiny ice crystals higher in a cloud.
— North Phoenix News (@NoPhoNews) February 21, 2019
The higher they go and the longer they’re suspended, the bigger hailstones can become, until they get heavy enough to overcome the updrafts and fall.
Sometimes the hail will get carried upward multiple times and develop layers, like an onion. If you could count the layers, you’d know how many times a hailstone travelled to the top of the thunderstorm.
Snow can also move up and down in storm clouds before it falls. But snow develops first as tiny ice crystals, which collide with other crystals that stick to form flakes that eventually succumb to gravity.
Most hail is the size of peas or marbles (I’d say we saw some marbles today). And yeah, that’s nothing…
“The largest hailstone recovered in the U.S. fell in Vivian, SD on June 23, 2010 with a diameter of 8 inches and a circumference of 18.62 inches,” according to the National Severe Storms Laboratory. “It weighed 1 lb 15 oz.”
SOURCES: NOAA; National Severe Storms Laboratory; “The Weather Book”